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Orbital imaging: Part 2. Intraorbital pathology
Clinical Radiology (2005) 60, 288–307
PICTORIAL REVIEW
Orbital imaging: Part 2. Intraorbital pathology R.I. Aviva,*, K. Miszkielb a
Department of Neuroradiology, Sunnybrook and Women’s College Hospital, Toronto, Canada; and bThe National Institute for Neurology and Neurosurgery and Moorfields Eye Hospital, London, UK
Received 4 August 2003; received in revised form 18 February 2004; accepted 5 May 2004
KEYWORDS Orbit; CT; MRI; Pathology
Several primary and secondary processes may affect the orbit. We present a review of intraorbital pathology utilising a compartmental approach guiding the differential diagnosis. Knowledge of the contents of each compartment facilitates the differential diagnosis. Globe pathology is not dealt with in this review. q 2005 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction The compartmental approach to orbital imaging discussed previously provides a useful guide to an approach to orbital pathology. Invariably it is possible to determine the compartment of origin of a lesion and provide an appropriate list of differential diagnoses. Ultimately, a biopsy will provide the definitive histology. Table 1 lists the orbital compartments and a list of differential diagnoses.
Intraconal space Within the intraconal compartment, it is useful to consider lesions arising from the optic nerve sheath (ONS) complex separately. Optic nerve glioma Is the commonest tumour arising from the ONS complex. It may be divided into those with a childhood onset having a variable but largely indolent course and an adult form, which is aggressive, associated with a high mortality. Histology reveals a low-grade astrocytoma usually of a pilocytic type in the childhood form and an anaplastic astrocytoma or glioblastoma multiforme in the adult form. The childhood form effects children younger than 10 years of age in 70% of * Guarantor and correspondent: R. Aviv, 36 Broadfields Avenue, Edgware HA8 8PG, UK. Tel.: C44-208-9586760. E-mail address: [email protected] (R.I. Aviv).
cases 1 without sex discrimination. The vast majority (90%) are less than 20 years of age at presentation. Any portion of the optic nerve, chiasm, tracts or radiations may be involved. Unilateral involvement is more common except in neurofibromatosis type I where bilateral involvement occurs. Fifteen to twenty percent of patients with a glioma of the optic pathway have neurofibromatosis.2,3 Lesions may be asymptomatic, detected during screening for neurofibromatosis, or present with reduced visual acuity and visual field defects, followed later by proptosis and optic atrophy. There is a spectrum of imaging features varying from tubular (Fig. 1) or fusiform (Fig. 2) enlargement with kinking due to a combination of neoplastic involvement and venous congestion4 to more globoid expansile lesions (Fig. 3). CT and MRI appearances depend on whether there is cyst formation or a mucinous component (Fig. 3). Appearances range from isodense with the optic nerve to hypodense on CT and increased T1 and T2 relaxation on MRI. The optic canal may be widened if the tumour involves the intracanalicular portion of the nerve.5 Enhancement after contrast is variable. It may be intense but usually less than that seen with meningioma. Fifty percent of patients presenting with the adult form of optic nerve glioma will have optic nerve and chiasmatic involvement.6 These patients usually die within a year of the diagnosis. The prognosis of childhood optic nerve glioma is no different in NF compared to those without (15 year survival was 81% and 76% respectively, not
0009-9260/$ - see front matter q 2005 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2004.05.018
Orbital imaging: Part 2. Intraorbital pathology
Table 1
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Orbital compartments, contents and pathology
Compartment
Contents
Pathology
Extraconal
Fat, lacrimal gland, bony orbit
Conal
Muscles
Intraconal
Fat, lymph nodes, vessels, nerves, optic nervesheath complex
Infection, neurofibroma, adenocarcinoma, mucoepidermoid, adenoid cystic carcinoma, carcinoma: primary (benign/malignant)/ secondary, neoplasia of bone, lymphoma Rhabdomyosarcoma, thyroid eye disease, idiopathic orbital inflammation (pseudotumour) Venolymphatic malformation, haemangioma, arteriovenous malformation, optic nerve meningioma/glioma, lymphoma Retinoblastoma, metastasis, melanoma
Globe
significant) despite NF patients having a longer mean time to tumour progression (8.37 years vs. 2.39 years).7,8 This is controversial and other authors have suggested that NF1 has a protective effect on patients with chiasmatic gliomas.9 The distribution of involvement differs in the two groups. Patients without NF are more likely to have hypothalamic and/or posterior tract involvement or chiasm involvement alone. There is no difference in distribution between the NF and nonNF group for isolated optic nerve glioma or chiasmatic involvement with one or both optic nerves involved. Meningioma The second most common tumour of the optic nerve sheath complex is meningioma. Distinction should be made between this primary origin as opposed to secondary orbital involvement from an intracranial source such as an intraosseous meningioma involving the greater wing of the sphenoid. These benign tumours arise from arachnoid cells within the leptomeninges. Very rarely, they may arise from arachnoid rest cells inside the orbit. Optic nerve sheath meningiomas constitute 3% of all orbital tumours. They are bilateral in 5% of cases, usually associated with neurofibromatosis type II, radiotherapy or meningiomatosis. Although benign, they are difficult to treat as complete removal along with the dura strips the optic nerve of its blood supply. These difficulties have led to alternative forms of treatment such as stereotactic radiotherapy.10 ONS Meningiomas present with slowly progressive, painless visual impairment with or without proptosis and optic atrophy. The central visual field is characteristically preserved for many years. Middle-aged women are most commonly affected. The tumour characteristically involves the ONS complex in a continuous rather than segmental fashion producing a fusiform (Fig. 4) or tubular
enlargement of the ONS, but globoid eccentric tumours are well recognized. This feature may help distinguish meningioma from schwannoma, which arises eccentrically, although meningiomas arising at the orbital apex may have a similar appearance. Meningioma may show calcification on CT and enhances uniformly after contrast administration producing a tramtrack sign (Fig. 4)11 due to the enveloped non-enhancing and attenuated optic nerve. The MRI equivalent is the doughnut sign on the coronal image. The sign is not specific and has variably been described in optic neuritis and idiopathic orbital inflammation (pseudotumour)12, 13 involvement. There may be hyperostosis (Fig. 4) and optic canal widening (Fig. 5)14 or narrowing usually associated with secondary orbital involvement and intracanalicular optic nerve spread respectively.15 MRI demonstrates a similar configuration with isointensity to the optic nerve on T1 and T2 although it may be low signal on T1 and high signal on T2. Fat saturated, contrast enhanced T1weighted images provide best lesion demonstration. In contradistinction to optic nerve glioma where the optic nerve is expanded, it may be compressed by the more intensely enhancing meningioma (Fig. 5). A cystic component may be identified between the tumour and the globe due to focal sheath dilatation (capping cyst) and has once been described as the cause of acute onset proptosis in this condition.16 Optic neuritis There are several causes of optic neuritis with multiple sclerosis being one of the most common. Seventy five percent of patients with multiple sclerosis will have involvement of the eye in the course of their illness.17 In 35% of patients with multiple sclerosis, visual dysfunction is the presenting feature with internuclear ophthalmoplegia developing in 35–50% of cases.18 Presentation is with reduced visual acuity over days with pain on
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eye movement and an afferent papillary defect. The mechanism is a T cell mediated response against myelin antigen. The aetiology is uncertain but is presumably related to genetic and ethnic factors and geographical location, with a greater incidence further away from the equator. MRI is the principle modality for the investigation of clinically suspected multiple sclerosis and provides paraclinical support for the diagnosis.19 Orbital findings include optic nerve enlargement in the acute stage with plaques of T2-weighted hyperintensity and localised or diffuse enhancement (Fig. 6). Intracranial demyelination may also be evident. Atrophy is present in the chronic stage. The length and position of lesions may have prognostic significance with long and intracanalicular lesions having a worse prognosis.20 Fat saturated imaging, which can be achieved by two means (STIR and SPIR—see part 1, technique), eliminate high signal from surrounding fat improving sensitivity.21 However, high signal within the CSF from increased T2-w and image distortion from magnetic field inhomogeneity complicate each sequence respectively. Combined water and fat suppression techniques (FLAIR/SPIR—see part 1, technique) are reported as further improving lesion detection by suppressing the CSF within the optic nerve sheath.22 Imaging specifically to look at the optic nerve where there is clinical certainty about the diagnosis of MS is unhelpful as only extremely rarely are there other causes for symptoms.23 Vascular tumours Refer to haemangiomas that should be distinguished from lymphangioma, venous-lymphatic malformations and arteriovenous malformations.24,25 These lesions have typical locations but may involve more than one compartment. Haemangioma and lymphangioma are discussed under the extraconal section. Venous lymphatic malformations Is a spectrum from predominantly venous malformations to lymphatic malformations (Fig. 7). Cavernous haemangioma (Fig. 8) is a misnomer used to describe a venous malformation that is usually intraconal but may be intraosseous and therefore extraconal. They present between 10 and 40 years of age with progressive enlargement Figure 1 (a)–(c). Axial T1-weighted unenhanced scan (a) showing isointense tubular thickening of the orbital segment of the left optic nerve (short black arrows), which is hyperintense on the T2-weighted coronal fat saturated sequence (b curved arrow). The affected segment of the nerve shows avid enhancement (c black !).
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resulting in proptosis and diplopia. Increased growth may occur during pregnancy or after trauma. They are well-defined (due to a fibrous pseudocapsule) ovoid lesions26 usually sparing the orbital apex. They rarely involve the globe but may result in remodelling of the orbital bone, consistent with a slow-growing benign lesion. Cavernous haemangiomas are usually low signal on T1weighted and increased on T2-weighted MRI with variable enhancement.27 The enhancement pattern is similar on CT and precontrast these lesions are hyperdense. Varix There is controversy as to whether this pathology is part of the lymphangioma spectrum or a discrete entity.28 The majority opinion is that it is a discrete entity. A varix is a dilated vein or group of veins that present with intermittent proptosis aggravated by increased intracranial pressure caused by the Valsalva manoeuvre or postural change due to their continuity with the systemic circulation in the majority of cases. They are of uncertain aetiology but theories include arteriovenous shunts and thrombosis. On imaging tubular masses are identified which may increase in size if the scans are acquired before and after Valsalva. The veins usually taper towards the apex and reveal no internal septation. Varices may show hyperdensity on CT precontrast and an absence of flow void in the context of thrombosis. Calcified phleboliths are pathognomonic if present (Fig. 9). There is an association with non-contiguous intracranial venous malformations in approximately 10% of cases and therefore investigations should include an assessment of the intracranial veins.29
Muscle cone
Figure 2 (a, b). On this axial T2-weighted image (a) there is fusiform thickening of the orbital segment of the left optic nerve and perineural spread (solid black arrow), the thickened sheath being markedly hyperintense. The posterior globe is flattened and proptosed (black !). The axial T1-weighted post-contrast image (b) shows avid enhancement of tumour and sheath within the orbit (short black arrow), but also sheath enhancement within the optic canal (long black arrow).
Pseudotumour (idiopathic orbital inflammation) Pseudotumour is characterised histologically by an inflammatory infiltrate of predominantly mature lymphocytes, plasma cells and macrophages and less commonly by a granulomatous infiltrate, desmoplasia and eosinophilia.30 Rarely multinucleated giant cells and non-caseating granuloma formation is present. The diagnosis is made after the exclusion of other pathologies including Wegener’s granulomatosis, sarcoid, systemic lupus erythematosis, polyarteritis nodosa, rheumatoid, Sjo ¨grens, lymphoproliferative disorders, metastasis and Erdheim-Chester. 31 Associated disorders include fibrosing mediastinitis, retroperitoneal
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Figure 4 (a, b). Two patients with bilateral tubular optic nerve sheath meningiomas. The axial post contrast CT shows tram-track hyperdensity (short black arrow) of the sheath enclosing an attenuated hypodense optic nerve (a). There is hyperostosis of the left anterior clinoid process (curved black arrow). (b) An axial post-contrast T1-weighted MRI shows clear evidence of early intracranial meningeal spread around the anterior clinoid processes (long black arrow) and planum sphenoidale (curved black arrow), which was not evident on the axial CT.
Figure 3 (a–c). Globoid expansion and enhancement of the left optic nerve within the orbit is shown on this T1weighted axial enhanced image (a), with an area of cystic change anteriorly behind the globe (long black arrow). Thickening and enhancement of the sheath is also present (short black arrow), although sheath and nerve appear to
be separated by a hypointense capsule (b) (black arrowhead) which does not enhance in (a). There is evidence of intracranial extension with cystic change within the affected left side of the chiasm on a coronal T2-weighted image (curved black arrow) (c).
Orbital imaging: Part 2. Intraorbital pathology
Figure 5 (a, b). A hyperintense fusiform intracanalicular optic nerve sheath meningioma protrudes into the orbital apex (black short arrow), on this axial T2weighted fat saturated image (a). Anterior to the tumour the optic nerve sheath is distended (black o), and the optic nerve itself is atrophic (long black arrow). The optic canal is widened. Enhancement of the meningioma is avid (black m) (b).
and hepatic fibrosis, Riedel’s thyroiditis and cholangitis. Any age group may be affected with adults in the 4th to 6th decade predominating. Unilateral involvement occurs in 85% of adults, but is more frequent in children.32 There is a spectrum of disease based on speed of onset, location and
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Figure 6 (a–c). Axial (a) and coronal (b) contrastenhanced CT and coronal fat-saturated post-contrast T1weighted MRI (c). There is diffuse enlargement of the right optic nerve sheath complex (black o) with enhancement.
extent of involvement. Inflammation may present acutely, subacutely or in a slowly progressive or chronic form. Disease may present in the anterior structures (periscleritis, sclerotendinitis, uveitis), within the lacrimal gland (lacrimal adenitis), within the apex (apicitis), diffusely (diffuse orbital inflammation), within the extraocular muscle (myositis) and involving the optic nerve (perineuritis). The disease process may spread intracranially to involve the cavernous sinus, infratemporal fossa as well as into the nasopharynx via the pterygopalatine fossa.33,34 The sclerosing form is thought to be a
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Figure 8 Enhanced axial CT of a cavernous haemangioma. There is a well-defined triangular shaped, retrobulbar intraconal and heterogeneously enhancing lesion (white *) splaying the rectus muscles (black arrow) and causing proptosis. The appearances are typical of a ‘cavernous haemangioma’.
Figure 9 Axial post contrast CT showing an ovoid intraconal and extraconal mass within the left orbit, with some areas of reduced enhancement (long black arrow). There is proptosis of the globe, and the numerous intralesional calcified phleboliths (short black arrow) are pathognomonic of varices. Figure 7 (a–c). Axial post contrast CT showing a welldefined right intra-conal mass anteromedially within the orbit, displacing and flattening the globe (short black arrow) (a). (b) The axial T2-weighted MRI shows the mass to be relatively hyperintense (curved arrow). (c) T1weighted image demonstrates focal areas of hyperintensity consistent with methaemoglobin (solid black arrow). Histology was that of a venolymphatic malformation.
subtype of orbital pseudotumour and presents in a chronic progressive form that is resistant to treatment. The presentation is determined by the above factors and range from acute onset of painful exophthalmos with adjacent features of inflammation (uveitis, scleritis) to cranial nerve involvement, painful ophthalmoplegia and forehead numbness due to III, IV, VI and V1 involvement in the cavernous sinus (Tolosa Hunt). Children have constitutional symptoms in 14% leading, erroneously, to the diagnosis of orbital cellulitis. The
Orbital imaging: Part 2. Intraorbital pathology
Figure 10 Orbital pseudotumour. Contrast enhanced orbital CT. There is diffuse infiltration of the right medial rectus (black r) with blurring of its edges due to involvement of the adjacent intra- and extra-conal fat. There is proptosis with preseptal soft tissue (short black arrow) and scleral thickening (long black arrow) and flattening of the posterolateral globe.
diagnosis is assisted by imaging features, which alone are non-specific. One or many of the following features may be present. There is focal or diffuse soft tissue within the orbit that enhances after contrast. The fat is infiltrated and streaky (dirty fat). Proptosis usually occurs (except in the sclerosing type) and there is extraocular muscle involvement with enlarged muscles with blurred edges due to adjacent fat involvement (Fig. 10). Muscle tendons as well as the optic nerve may be enlarged. The lacrimal gland is the most frequently involved orbital structure. There is diffuse glandular involvement with spilling over of the inflamma-
Figure 11 Axial CT showing diffuse infiltration of the orbit by a soft tissue mass filling intraconal and extraconal compartments, with resultant flattening of the proptosed globe (thick black arrow). The left ethmoid air cells (curved black arrow) and anterior clinoid process (black c) are less well pneumatised. The lamina papyracea and lateral orbital bony margin appear sclerotic (short black arrows).
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tory process to the surrounding tissues, most commonly the lateral rectus, resulting in an indistinct border. Bone erosion is rare but remodelling may occur. Bone sclerosis occurs in 17% of cases presumed to be due to a low-grade osteitis usually associated with the sclerosing subset (Fig. 11). The infiltrate is hypointense to fat on T1 and isointense on T2 which does help to distinguish pseudotumour from tumour although other aetiologies such as sarcoid may have similar signal. Proliferating cell nuclear antigen (PCNA), a marker of nuclear protein in dividing cells will not be elevated in pseudotumour or low grade lymphoma compared with increased titres in high grade lymphoma. Furthermore, the B cell to T cell ratio is increased in lymphoid tumours and together with the PCNA are useful adjuncts to clinical and imaging features. Treatment is with steroids with dramatic response that is helpful in confirming the diagnosis. The sclerosing type responds poorly. Lymphoma has also been shown to respond in a similar way and this has been used as an argument against the prevailing opinion as to the usefulness of oral steroids.35 Thyroid eye disease Is the most common disorder affecting the orbit, usually presenting in middle age women. The orbitopathy may precede thyroid disease or occur with euthyroid or hypothyroidism, but is most common in the context of Graves’ disease. There is usually an acute presentation with exacerbations and remissions becoming chronic over months to years.36 Patients with known Graves’ disease may have asymptomatic myopathy in up to 71% of cases.37 The acute phase may simulate an orbital cellulitis clinically with injection, chemosis and lid swelling. In the chronic phase proptosis, diplopia due to a restrictive myopathy and lid lag are demonstrated. Pain is not usually a feature until late, a distinguishing feature from inflammatory pseudotumour. Inflammation is immune mediated and histologically there is an inflammatory infiltrate of lymphocytes and plasma cells predominantly with the production of hyaluronic acid, a mucopolysaccharide that is deposited within the extraocular muscles resulting in fibrosis. No eosinophil infiltration or lymphoid follicle formation occur as may be the case in idiopathic inflammation. The inferior rectus is most often involved followed by the medial rectus and superior muscle complex. There is a strong tendency to bilaterality. Isolated lateral rectus involvement is rare and should prompt consideration of alternative diagnoses (idiopathic inflammation, myositis, lymphoma, metastasis). There
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Figure 12 (a–c) Axial and coronal CT after contrast administration in two different patients with Grave’s ophthalmopathy. (a, b) There is fusiform, symmetrical enlargement of the medial rectus muscle (black r) and to a lesser degree the lateral rectus muscle (black l). The tendons are spared producing a ‘bottle neck’ appearance (long black arrow). There is bilateral proptosis. No inflammatory change is present within the fat. The crowding of the orbital apex is best appreciated on the coronal image (b). (c) Contrast enhanced coronal view of the orbit demonstrating diffuse inflammatory changes within the orbital fat (black f). (d) Fat saturated coronal T2-weighted and gadolinium enhanced T1-weighted images. There is diffuse extraocular muscle enhancement with lesser involvement of the lateral rectus. Illdefined signal hyperintensity is present within the orbital fat above the inferior rectus (short black arrow). (e) After gadolinium, there is diffuse enhancement of the extraocular muscles and the orbital fat.
is a strong association between smoking and the risk and severity of developing orbitopathy in Graves’ disease. Radiologically, there is increase in the volume of orbital fat, which is a non-specific sign also seen in obesity. The fat is initially unaffected (Fig. 12(a)
and (b)). Enlarged muscles produce apical crowding and venous congestion. The inflammatory response spills over into the intraorbital fat and together produce streaking within the fat (‘dirty fat’) (Fig. 12(c)). The muscles are usually involved bilaterally with a fusiform appearance due to characteristic
Orbital imaging: Part 2. Intraorbital pathology
Figure 13 Axial (a) and coronal T2-weighted (b) images showing a lobulated largely hyperintense extraconal mass superiorly within the right orbit consistent with a neurofibroma of the frontal nerve (black n). There is thinning of the orbital roof locally due to pressure remodelling (thick black arrow). Note the enlargement of the ipsilateral extra-ocular muscles due to thyroid eye disease.
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optic nerve sheath complex may also be enlarged and the superior ophthalmic vein congested. The delicate lamina papyracea may be moulded by the muscle enlargement. These imaging features are efficiently diagnosed and monitored with CT, especially acquired in the coronal plane, with the exception of apical crowding which is more readily assessed on coronal MRI. MRI (Fig. 12(d) and (e)) may be used to predict the response to therapy by distinguishing between muscle inflammation and fibrosis on the basis of T2-weighted relaxation time.38 A fat saturated T2 sequence is particularly good for this application. Similarly using the same criteria, MRI has been used to monitor response to therapy. The natural history of thyroid eye disease is that approximately 20% of patients will require a surgical procedure with the average time to surgery being 3.3 year.39 The vast majority require supportive medical or no treatment. Corticosteroids produce improvement in symptoms in up to 60% of patients within 24–72 h, but relapse occurs after dose reduction. The amount of disease activity predicts the response to therapy. Side effects are common restricting their long-term use. Other treatments include orbital irradiation40 and decompression performed for optic neuropathy, optic nerve compression, medically refractory disease and exposure keratopathy. Imaging plays an important role in distinguishing causes of muscle enlargement in combination with clinical features. Tendinous involvement is more suggestive of pseudotumour, although the absence of this sign does not exclude pseudotumour. Graves’ is more frequently bilateral than pseudotumour and often symmetric. Pseudotumour results in blurred muscle edges whereas initially in thyroid disease these are distinct. Pain is uncommon in thyroid ophthalmopathy as opposed to pseudotumour. Metastases tend to be more localized and nodular and lymphoma tends to cause greater muscle enlargement over a longer timecourse and can respond to steroids. Lacrimal gland involvement is common in lymphoma and pseudotumour but is rare in thyroid disease (although may occur).
Extraconal space sparing of the muscle tendons. Inflammation is initially limited to the muscle, which therefore has a crisp well-defined border in distinction to pseudotumour. The combination of extraocular muscle enlargement and increase intraorbital fat produces proptosis. Optic nerve compression due to apical crowding is rare (!10%), but results clinically in decreased visual acuity and fields. The retro-orbital
Schwannoma/neurofibroma Schwannoma and neurofibroma share similar appearances and nerve involvement and are considered jointly. Schwannoma is more common and comprises up to 6% of orbital masses.41 Both tumours are benign and slow growing presenting more commonly in the adult
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Figure 14 (a, b) Axial enhanced orbital CT and surface shaded 3D CT. (a) There is a heterogeneous orbital mass occupying both intra- and extra-conal spaces extending anteriorly into the preseptal soft tissues and posteriorly into the cavernous sinus (black c), middle cranial fossa (where a fleck of calcification is present, black long arrow) and cerebellopontine angle cistern. There is widening of the superior orbital fissure (curved black arrow (b), remodelling of the lamina papyracea (short black arrow) and ethmoid air cells. There is dysplasia of the greater wing of sphenoid (black s) with temporal bossing producing enlargement of the middle cranial fossa subarachnoid space. Note the presence of a further plexiform neurofibroma overlying the ipsilateral temporal fossa (black t) and the widened optic nerve canal (solid black arrow (b)) secondary to an optic nerve glioma in this patient with neurofibromatosis 1.
R.I. Aviv, K. Miszkiel
Figure 15 (a–c). (a, b) Pre- and post-contrast orbital CT in a young male infant with a capillary haemangioma. There is an extraconal lobulated enhancing mass lesion located in the superomedial quadrant occupying the pre and post septal position (black h). The globe is displaced inferolaterally. (c) Coronal fat saturated T2-weighted scan (different patient) demonstrates a hyperintense lobulated extraconal mass with flow voids (black arrows) consistent with a haemangioma.
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Figure 16 Venolymphatic malformation with features of lymphatic malformation. Unenhanced, axial CT mid orbits. There is a well-defined intraconal cystic lesion with fluid-fluid levels (short black arrows) displacing the globe anteriorly and the optic nerve sheath complex medially (long black arrow).
population except in the context of neurofibromatosis. The most commonly affected nerves are the sensory branches of V1 accounting for their position in the superior orbit (Fig. 13).42 Painless proptosis is the mode of presentation. Imaging depends on histological characteristics for schwannomas with Antoni A lesions being more uniform than Antoni B tumours. They are usually hypointense on T1-w and hyperintense on T2-w. Both enhance with contrast. The benign nature of these lesions may lead to expansion of the orbit and bone remodelling. Plexiform neurofibromata (Fig. 14) are associated with hypoplasia of the greater wing of the sphenoid and macrophthalmia in neurofibromatosis type I. Neurofibromata may be distinguished by the presence of calcification that is rarely seen in schwannomas. The optic nerve may be displaced or involved. Haemangioma Capillary haemangiomas (Fig. 15) differ in clinical presentation, location and age of presentation. Capillary haemangioma is usually extraconal, situated in the upper medial (superomedial) quadrant with associated cutaneous malformations over the face. They are present at birth, grow rapidly in the first year of life and regress usually by 7 to 10 years of age.25 They are less well defined than the socalled cavernous haemangiomas (venous malformations). They more commonly arise extraconally and anteriorly, but may infiltrate posteriorly to involve the orbital apex and extend intracranially
through the superior orbital fissure or optic canal. Intraconal extension also occurs. Flow voids may be identified within and on the surface of capillary haemangiomas on T2-weighted images, which is a helpful distinguishing feature from lymphangioma. A prominent arterial supply is usually demonstrable from either the external or the internal carotid circulation. The signal intensity is determined by the amount of fibrosis, calcification and haemosiderin deposition after haemorrhage. The appearance prior to delayed scans may be indistinguishable from neurofibroma, schwannoma and haemangiopericytoma. Venous lymphatic malformations Lymphatic malformation comprises a network of bloodless spaces lined by flattened poorly supported endothelial cells lying in a loose stroma of lymphoid tissue and small blood vessels. This explains the propensity for sudden increase in size due to haemorrhage or viral infection.43 Imaging demonstrates a lobular, infiltrating extraconal mass that may remodel the orbit. Density and signal depend on the presence of haemorrhage that may also cause fluid-fluid levels (Fig. 16). Calcification is rare. Flow voids are absent which helps distinction from capillary haemangioma. Rim enhancement may occur after contrast administration. These lesions can be treated with good success with Sodium tetradecylsulphate injection44 Lymphoma Lymphoma
is
discussed
here
as
most
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Figure 17 (a–d) Manifestations of orbital lymphoma. (a) Unenhanced axial CT with well-defined homogenous unilateral lesion (white *) centred on the lacrimal gland with thinning of the adjacent lateral orbital wall (white arrow). The lesion displaces the globe but the shape of the lesion conforms to its outline (black arrows). (b) A well-defined, uniformly enhancing, intraconal, retrobulbar mass (white *) and additional lacrimal involvement (black *). (c), (d) Infiltrating lymphoma involving intraconal and conal compartments, cavernous sinus, masticator space and temporal fossa. There is an ill-defined, uniformly enhancing mass infiltrating rectus muscles (white arrowhead) and extending posteriorly through the superior orbital fissure into the anterior cavernous sinus (black arrow). There is preseptal and temporal fossa soft tissue thickening (white *). Coronal images reveal extension through the inferior orbital fissure (white circle) into the masticator space (black arrowhead), infraorbital canal (white arrowhead) and suprazygomatic temporal fossa (white *).
lymphoproliferative disease affects the superolateral orbital quadrant with the lacrimal gland being most commonly affected (Fig. 17(a)). Any compartment, however, may be affected although primary involvement of the extraocular muscles is rare. Lymphoma accounts for 10–15% of orbital masses. Seventy-five percent of patients with orbital lymphoma will eventually have systemic disease, usually non-Hodgkin’s lymphoma (NHL). One percent of patients will have orbital involvement during the course of their illness45 but presentation with orbital involvement is rare.
Presentation is usually in adults in the sixth to seventh decade46 and women are more commonly affected. Painless downward proptosis is therefore the most common mode of presentation.47 The imaging findings are numerous with a spectrum of a well-defined mass lesion (Fig. 17(b)) to the more common ill-defined infiltration (Fig. 17(c) and (d)).48 The tumour is conformable to the surroundings structures and bone erosion or sclerosis is uncommon. CT characteristically displays a dense mass. The signal characteristics are determined by cell
Orbital imaging: Part 2. Intraorbital pathology
Figure 18 Axial contrast enhanced CT showing diffuse infiltration of the intraconal and extra-conal compartments by soft tissue, from metastatic scirrhous carcinoma of the breast. This results in bilateral enophthalmos. The fibrous form of idiopathic orbital inflammation could have similar appearances.
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Figure 20 Enhanced axial CT in a young child with partially treated neuroblastoma metastases. There is an enhancing soft tissue mass (compared with unenhanced brain imaging-not shown) centred on the greater wing of sphenoid projecting anteromedially into the extraconal space (with deviation of the lateral rectus muscle (short black arrow)) and into the middle cranial and temporal fossa (long black arrow). The bone has a permeative pattern with a central lytic component. Dural enhancement is seen along the anterior middle cranial fossa (curved black arrow).
Figure 19 (a, b). Contrast enhanced axial CT of orbit and brain with biopsy proven lacrimal and brain melanoma metastasis. (a) There is an irregular, enhancing (when compared with unenhanced head imaging-not shown) lobulated soft tissue density of the right lacrimal gland (short black arrow) in association with (b) a left frontoparietal intra-axial lesion with surrounding vasogenic oedema (long black arrow). There is gradation of density within the brain lesion suggesting haemorrhage (curved black arrow).
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Figure 22 (a, b). (a) Enhanced axial CT and (b) Axial T2 weighted MRI (different patients) adenoid cystic carcinoma. (a) There is a heterogeneous partly calcified lesion (black *) arising from the lacrimal gland invading the adjacent greater wing of sphenoid and orbital plate of the zygoma (white *) with anteromedial globe displacement. (b) Different patient demonstrating mixed signal with cystic component (black *) lying posterior to a calcific focus (white arrow) embedded in isointense tumour. No bone destruction. Figure 21 (a) Axial CT and (b, c) T2- and enhanced T1weighted MRI (different patient) pleomorphic adenoma. There is a well-circumscribed oval lesion (white *) arising from the orbital lobe of the lacrimal gland with scalloping of the adjacent orbital margin (black arrow) and inferomedial globe displacement. No calcification or sclerosis. (b) The lesion is heterogeneously isointense rather than hyperintense, (c) and enhances avidly (black *).
packing and may be low on T1 and T2 weighted images where there is dense packing or high on T2 where packing is less dense. Contrast enhancement is variable. Bilateral orbital masses should raise the suspicion of lymphoma. Lymphoma may have appearances identical to idiopathic orbital
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inflammation. Increased proliferating cell nuclear antigen (PCNA) and an increased B cell to T cell ratio may be useful discriminators.49 NHL of the orbit responds to both chemotherapy and radiotherapy. Miller demonstrated that patients with unfavourable histology receiving both treatments did better than those receiving chemotherapy alone.50 Radiotherapy alone is effective for localised histologically more favourable subtypes of lymphoma. Metastases and extraorbital malignancy Common primary sources for orbital metastases include breast (Fig. 18), lung, stomach, thyroid, renal carcinoma and melanoma (Fig. 19). The orbit is a common site for neuroblastoma metastasis in childhood (Fig. 20). Involvement is usually extraconal involving the retrobulbar fat, orbital bone and the lacrimal gland, although the conal muscles are primarily involved in less than 10% of cases.51 Schirrous breast metastasis produce enophthalmos that may mimic idiopathic orbital inflammation (Fig. 18). Painful proptosis is the most common presentation except when the metastasis is a scirrhous breast metastasis when enophthalmos occurs. The orbit may be involved from extension of malignancy from the sinuses, nasopharynx and globe. Tumour is often irregular and poorly defined with signal intensity similar to muscle and variable enhancement. Melanoma may demonstrate hyperdensity on CT. Simultaneous brain metastases are seen in two thirds of patients with orbital metastases.
Figure 23 (a–c) Axial and coronal orbital CT after contrast administration in two different patients. (a) There is preseptal soft tissue thickening (solid black arrow) and oedema extending posteriorly to involve the temporal muscle (curved black arrow) secondary to orbital cellulitis. No postseptal extension. The cavernous sinus and superior ophthalmic vein (not shown) were patent. (b, c) There is an intraorbital abscess with a thin enhancing wall within the superior (curved black arrow) and medial extraconal space. The globe is proptosed and displaced inferolaterally. A focal defect is present within the lamina papyracea with opacification of the ipsilateral frontal recess and ethmoid sinuses (short black arrow). No intracranial extension was present.
Lacrimal gland Pathology affecting the lacrimal gland should be divided into two groups based on the clinical history and examination. The first group are the primary benign neoplasms of epithelial origin accounting for 50% of epithelial origin tumours. These present with progressive, painless swelling without radiologically sinister features of invasion. One such tumour the pleomorphic adenoma (Fig. 21) should not be biopsied due to local seeding, but should be excised completely.52 These tumours are distinguished by their contour and the appearance of the lacrimal fossa.53,54 They are well-defined lesions that involve the orbital surface of the lacrimal gland (with or without posterior extension) and mould the surrounding bone without destruction although occasionally one may see sclerosis. The second group includes the other 50% of epithelial tumours, which are malignant, including adenoid cystic (Fig. 22) or mucoepidermoid carcinoma, metastasis, lymphoproliferative disease (primary
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or secondary) and inflammatory processes such as idiopathic inflammation of the orbit and Wegener’s. Here the history is shorter, there may be pain and radiologically sinister features may be present. Imaging is non-specific. Key features helping in the diagnosis include the presence of pain in association with a firm mass in a young patient with the peak age being the 4th decade. The malignant epithelial lesions have a less well-defined or serrated border and there is a propensity to early infiltration along nerves with satellite lesions. Pressure erosion of the lacrimal fossa is common and bone erosion is occasionally seen. Calcification is more common in malignancy than pleomorphic adenoma. 55 Mucoepidermoid carcinoma may be hyperintense on T1. Lymphoma and pseudotumour are discussed elsewhere but mould to the surrounding structures and infiltrate the gland in its entirety (including the palpebral lobe) in contradistinction to epithelial tumours. The lacrimal gland is amenable to biopsy, which is often the method of diagnosis except where a pleomorphic adenoma is suspected clinically based on the features discussed above.
Figure 24 (a–c). (a, b) Enhanced axial CT (soft tissue and bone windows) and (c) T1-weighted gadolinium enhanced images of a dermoid. (a) There is a 2 cm well defined fat density (*) lying adjacent to the orbital surface of the zygomatic bone extending more superiorly (b) into a corticated bone defect (white arrow). (c) Increased signal consistent with fat was demonstrated both pre- (not shown) and post gadolinium although difficult to make out without fat saturation due to inflammatory changes post dermoid rupture (black arrow).
Infection The orbit may be involved in infection from the sinuses, face, less commonly from dental disease, via haematogenous spread, and direct trauma with or without foreign body penetration. Infection is usually caused by Staphylococcus or Streptococcus. The spread of infection from the paranasal sinuses may occur by direct penetration of the thin-walled lamina papyracea, which does not constitute a significant barrier to infection. Alternatively, infection may spread through the numerous communicating venous channels or diploic veins of Breschet. The periosteum of the orbit or periorbita is a tough layer which is loosely attached to much of the orbit except at the optic canal, superior orbital and inferior orbital fissure where it fuses with the dura and anteriorly to the orbital rim and lacrimal sac fossa. Anteriorly it also contributes to the orbital septum thus forming a formidable barrier to spread of infection from the preseptal region (Fig. 23(a)). Fusion with the dura implies a continuous potential space between the subperiosteal space and the epidural space explaining the complication of extradural brain abscess. Intracranial spread of infection may also progress to meningitis, subdural or parenchymal abscess. Venous drainage from the angular vein of the face through superior and inferior ophthalmic veins allows
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spread of infection intracranially and potentially into the masticator space through their communications with the cavernous sinus and pterygoid plexus. Thrombosis of these venous confluences may also occur. Imaging features vary according to the stage of progression of infection originally described by Chandler and modified by Lemke.56 An important distinction between an orbital phlegmon and a subperiosteal abscess can be made. In the former, there is heterogeneous increased tissue along the orbital wall with fat replacement and tissue within the subperiosteal space. In abscess formation, a medical and surgical emergency, there is increased intraocular pressure due to infective subperiosteal material that forms a ring-enhancing lesion (Fig. 23(b) and (c)) that may have an air fluid level within it, displacing the medial rectus muscle. Adjacent paranasal sinus disease is usual. There may be osteomyelitis of adjacent orbital bone. Treatment is with intravenous antibiotics and surgical drainage. Harris examined the size and radiodensity of subperiosteal abscesses in 37 patients less than 9 years of age. He noted an increase in the size of the abscess during the initial few days of antibiotic treatment. The increase in size had no effect on outcome.57 He found the initial CT scan was not predictive of the patient’s clinical course and advised medical treatment only unless there was an indication for surgical intervention such as impaired vision and intracranial infection.
Figure 25 (a–c). Axial CT images from two patients with histologically proven orbital amyloid. In image (a) there is enlargement of the left lacrimal gland (long black arrow). The anterolateral right orbital mass (b and c) contains foci of dystrophic calcification (short black arrow) within it but also within the temporal fossa. There is sclerosis of the zygoma (black z).
Dermoid cyst The sequestration of ectodermal components within the developing orbital bone usually occurs along the superolateral orbital margin at the zygomaticofrontal suture although the frontoethmoidal suture, superomedially, is the next most common site. Dermoid cysts are the most common congenital lesions of the orbit. They are well-defined slow growing lesions lying within the extraconal space and have local mass effect on the bone with erosion and remodelling. Occasionally presentation may be acute after rupture (Fig. 24), simulating an acute inflammation. MRI demonstrates a lesion with hyperintensity on T1 closely applied to the overlying bone with a tail of tissue extending into the bone. If the secretory elements predominate within the dermoid, the lesion may have signal characteristics similar to epidermoids. There may be a fat-fluid levels and calcification. Very occasionally, rim enhancement is seen if contrast is administered.
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Amyloid The orbit may be involved with primary or less commonly secondary amyloid. Deposition of B pleated proteinaceous sheets occurs in the upper eyelid, lacrimal gland and extraocular muscles. Enlargement occurs and calcification is not uncommon (Fig. 25). The signal intensity on MRI is governed by the presence of calcium, which renders the tissue hypointense, otherwise in the absence of calcification the tissue resembles muscle on all sequences.
Conclusion We have presented a pictorial review of common intraorbital lesions using a compartmental approach. We acknowledge that several pathological processes may involve more than one space, but we have attempted to classify pathologies under the most common presenting compartment. Knowledge of the contents of each compartment provides a cue for the differential diagnosis in each compartment.
Acknowledgements Dr G Quaghebeur for review of an early manuscript and useful suggestions.
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9. Rush JA, Younge BR, Campbell RJ, MacCarty CS. Optic glioma: long-term follow-up of 85 histopathologically verified cases. Ophthalmology 1982;89:1213–9. 10. Hodes JE, Sanders M, Patel P, Patchell RA. Radiosurgical management of meningiomas. Stereotact Funct Neurosurg 1996;6:15–18. 11. Johns TT, Citrin CM, Black J, Sherman JL. CT evaluation of perineural orbital lesions: evaluation of the ‘tramtrack sign’. AJNR Am J Neuroradiol 1984;5:587–90. 12. Som PM, Curtin HD. Head and neck imaging, 3rd ed. St Louis: Mosby; 1996. 13. Ing EB, Garrity JA, Cross SA, Ebersold MJ. Sarcoid masquerading as optic nerve sheath meningioma. Mayo clin Proc 1997;72:38–43. 14. Lloyd GA. Primary orbital meningioma. A review of 41 patients investigated radiologically. Clin Radiol 1982;33: 181–7. 15. Miller NR, Golnik KC, Zeidman SM, North RB. Pneumosinus dilatans: a sign of intracranial meningioma. Surg Neurol 1996;46:471–4. 16. Laitt RD, Kumar B, Leatherbarrow B, Bonshek RE, Jackson A. Cystic optic nerve meningioma presenting with acute proptosis. Eye 1996;10:744–6. 17. Reulen JP, Saunders EA, Hogenhuis LA. Eye movement disorders in multiple sclerosis and optic neuritis. Brain 1983;106:121–40. 18. Muri RM, Meienberg O. The clinical spectrum of INO in MS. Arch Neurol 1985;42:851–5. 19. Thompson AJ, Montalban X, Barkhof F, Brochet B, Filippi M, Miller DH, Polman CH, Stevenson VL, McDonald WI. Diagnostic criteria for primary progressive multiple sclerosis: a position paper. Ann Neurol 2000;47:831–5. 20. Youl BD, Turano G, Miller DH, Towell AD, MacManus DG, Moore SG, Jones SJ, Barrett G, Kendall BE, Moseley IF. The pathophysiology of acute optic neuritis: an association of gadolinium leakage with clinical and electrophysiological deficits. Brain 1991;114:2437–50. 21. Gass A, Mosely IF, Barker GJ, Jones S, MacManus D, MacDonald WI, Miller DH. Lesion discrimination in optic neuritis using high-resolution fat-suppressed fast spin-echo MRI. Neuroradiology 1996;38:317–21. 22. Jackson A, Sheppard MS, Laitt RD, Kassner A, Moriarty D. Optic Neuritis: MRI imaging with combined fat- and watersuppression techniques. Radiology 1998;206:57–63. 23. Optic Neuritis Study Group. The clinical profile of optic neuritis: experience of the Optic Neuritis Treatment Trial. Arch Ophthalmol 1991;109:1673–8. 24. Mulliken JB. Vascular malformations of the head and neck. In: Mulliken JB, Young AE, editors. Vascular birthmarks: haemangiomas and vascular malformations. Philadelphia: WB Saunders Co; 1988. 25. Mulliken JB, Glowacki J. Haemangiomas and vascular malformations in infants and children: a classification based on endothelial characteristics. Plast Reconstr Surg 1982;69:412–22. 26. Davis KR, Hesselink JR, Dallow RL, Grove Jr AS. CT and ultrasound in the diagnosis of cavernous haemangioma and lymphangioma of the orbit. J Comput Assist Tomogr 1980;4: 98–104. 27. Wilms G, Raat H, Dom R, Thywissen C, Demaerel P, Dralands G, Baert AL. Orbital Cavernous haemangioma: findings on sequential Gd-enhanced MRI. J Comput Assist Tomogr 1995;19:548–51. 28. Wright JE, Sullivan TJ, Garner A, Wulc AE, Moseley IF. Orbital venous anomalies. Ophthalmology 1997;104:905–13. 29. Katz SE, Rootman J, Vangveeravong S, Graeb D. Combined
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venous lymphatic malformations of the orbit (so-called lymphangiomas). Associated with non-contiguous intracranial vascular anomalies. Ophthalmology 1998;105:176–84. Snebold NG. Orbital pseudotumour syndromes. Curr Opin Ophthalmol 1997;8:41–4. Murray D, Marsall M, England E, Mander J, Chakera TM. Erdheim-chester disease. Clin Radiol 2001;56:481–4. Jakobiec FA, Adams AP, Pineda II RA. Non-infectious inflammatory disorder of the eye and adnexa. Int Ophthalmol Clin 1996;36:161–77. Han MH, Kim MS, Chang KH, Kim KH, Yeon KM, Han MC. Fibrosing inflammatory pseudotumours involving the skull base: MR and Ct manifestations with histopathological comparison. AJNR Am J Neuroradial 1996;17:515–21. Kaye AH, Hahn JF, Craciun A, Hanson M, Berlin AJ, Tubbs RR. Intracranial extension of inflammatory pseudotumour of the orbit. Case Report. J Neurosurg 1984;60:625–9. Mombaerts I, Schlingemann RO, Goldschmeding R, Koorneef L. Are systemic corticosteroid useful in the management of orbital pseudotumours? Ophthalmology 1996;103:521–8. Prummel MF, Wiersinga WM. Medical management of Graves’ ophthalmopathy. Thyroid 1995;5:231–4. Villadolid MC, Yokoyama N, Izumi M, Nishikawa T, Kimura H, Ashizawa K, Kiriyama T, Uetani M, Nagataki S. Untreated Graves’ disease patients without clinical ophthalmopathy demonstrate a high frequency of extraocular muscle (EOM) enlargement by magnetic resonance. J Clin Endocrinol Metabol 1995;80:2830–3. Utech CI, Khatibnia U, Winter PF, Wulle KG. MR T2 relaxation time for the assessment of retrobulbar inflammation in Graves’ ophthalmopathy (letter). Thyroid 1995;5:185–93. Bartley GB, Fatourechi V, Kadrmas EF, Jacobson SJ, Ilstrup DM, Garrity JA, Gorman CA. The treatment of Graves’ ophthalmopathy in an incidence cohort. Am J Ophthalmol 1996;121:200–6. Nakahara H, Noguchi S, Murakami N, Morita M, Tamaru M, Ohnishi T, Hoshi H, Jinnouchi S, Nagamachi S, Futami S, Watanabe K. Graves ophthalmopathy: MR evaluation of 10Gy versus 24-Gy irradiation combined with systemic steroids. Radiology 1995;196:857–62. Chisholm LA, Polyzoidis Z. Recurrence of benign orbital neurolemmoma (schwannoma) after 22 years. Can J Ophthalmol 1982;17:271–3. Rootman J, Goldberg C, Robertson W. Primary orbital schwannomas. Br J Ophthalmol 1982;66:192–204. Mafee MF, Putterman A, Valvassori GE, Campos M, Capek V.
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Orbital space-occupying lesions: role of computed tomography and magnetic resonance imaging. An analysis of 145 cases. Radiol Clin North Am 1987;25:529–59. Svendsen PA, Wikholm G, Rodriguez M, Ericksson P, Frisen L, Stromland K, Seregard S. Direct puncture and sclerotherapy with sotradecol. Orbital lymphatic malformations. Intervent Neuroradiol 2001;7:193–9. Jones IS, Jakobiec FA, editors. Diseases of the orbit. Hagerstown: Harper and Row; 1979. Flanders AE, Espinosa GA, Markiewicz DA, Howell DD. Orbital lymphoma: role of CT and MRI. Radiol Clin N Am 1987;25: 601–13. Yeo JH, Jakobiec FA, Abbott GF, Trokel SL. Combined clinical and computed tomographic diagnosis of orbital lymphoid tumours. Am J Ophthalmol 1982;94:235–45. Weber A, Jacobiec FA, Sabates NR. Lymphoproliferative disease of the orbit. Neuroimaging Clin North Am 1996;6: 93–111. Mauriello JA, Piacentini M, Pokorny KS, Mostafavi R, Yepez M, et al. The role of proliferating cell nuclear antigen (PCNA) in differentiating idiopathic orbital inflammatory disease and lymphoid proliferations. Ophthal Plast Reconstr Surg 1997;13:26–30. Miller TP, Dahlberg S, Cassady JR, Adelstein DJ, Spier CM, Grogan TM, et al. Chemotherapy alone compared with chemotherapy plus radiotherapy for localized intermediate and high-grade non-Hodgkin’s lymphoma. N Engl J Med 1998; 339:21–6. Rothfus WE, Curtin HD. Extraocular muscle enlargement: a CT review. Radiology 1984;151:677–81. Wright JE, Stewart WB, Krohel GB. Clinical presentation and management of lacrimal gland tumours. Br J Ophthalmol 1979;63:600–6. Stewart WB, Krohel GB, Wright JE. Lacrimal gland and fossa lesions: an approach to diagnosis and management. Ophthalmology 1979;86:886–95. Jakobiec FA, Yeo JH, Trokel SL, Abbott GF, Anderson R, Citrin CM, Alper MG. Combined clinical and computed tomographic diagnosis of primary lacrimal fossa lesions. Am J Ophthalmol 1982;94:785–807. Mafee MF, Haik BG. Lacrimal gland and fossa lesions: role of computed tomography. Radiol Clin North Am 1987;25: 767–79. Lemke BN, Gonnering RS, Weinstein JM. Orbital cellulitis with periosteal elevation. Ophthal Plast Reconstr Surg 1987; 3:1–7. Harris GJ. Subperiosteal abscess of the orbit: computed tomography and the clinical course. Ophthal Plast Reconstr Surg 1996;12:1–8.
PICTORIAL REVIEW
Orbital imaging: Part 2. Intraorbital pathology R.I. Aviva,*, K. Miszkielb a
Department of Neuroradiology, Sunnybrook and Women’s College Hospital, Toronto, Canada; and bThe National Institute for Neurology and Neurosurgery and Moorfields Eye Hospital, London, UK
Received 4 August 2003; received in revised form 18 February 2004; accepted 5 May 2004
KEYWORDS Orbit; CT; MRI; Pathology
Several primary and secondary processes may affect the orbit. We present a review of intraorbital pathology utilising a compartmental approach guiding the differential diagnosis. Knowledge of the contents of each compartment facilitates the differential diagnosis. Globe pathology is not dealt with in this review. q 2005 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction The compartmental approach to orbital imaging discussed previously provides a useful guide to an approach to orbital pathology. Invariably it is possible to determine the compartment of origin of a lesion and provide an appropriate list of differential diagnoses. Ultimately, a biopsy will provide the definitive histology. Table 1 lists the orbital compartments and a list of differential diagnoses.
Intraconal space Within the intraconal compartment, it is useful to consider lesions arising from the optic nerve sheath (ONS) complex separately. Optic nerve glioma Is the commonest tumour arising from the ONS complex. It may be divided into those with a childhood onset having a variable but largely indolent course and an adult form, which is aggressive, associated with a high mortality. Histology reveals a low-grade astrocytoma usually of a pilocytic type in the childhood form and an anaplastic astrocytoma or glioblastoma multiforme in the adult form. The childhood form effects children younger than 10 years of age in 70% of * Guarantor and correspondent: R. Aviv, 36 Broadfields Avenue, Edgware HA8 8PG, UK. Tel.: C44-208-9586760. E-mail address: [email protected] (R.I. Aviv).
cases 1 without sex discrimination. The vast majority (90%) are less than 20 years of age at presentation. Any portion of the optic nerve, chiasm, tracts or radiations may be involved. Unilateral involvement is more common except in neurofibromatosis type I where bilateral involvement occurs. Fifteen to twenty percent of patients with a glioma of the optic pathway have neurofibromatosis.2,3 Lesions may be asymptomatic, detected during screening for neurofibromatosis, or present with reduced visual acuity and visual field defects, followed later by proptosis and optic atrophy. There is a spectrum of imaging features varying from tubular (Fig. 1) or fusiform (Fig. 2) enlargement with kinking due to a combination of neoplastic involvement and venous congestion4 to more globoid expansile lesions (Fig. 3). CT and MRI appearances depend on whether there is cyst formation or a mucinous component (Fig. 3). Appearances range from isodense with the optic nerve to hypodense on CT and increased T1 and T2 relaxation on MRI. The optic canal may be widened if the tumour involves the intracanalicular portion of the nerve.5 Enhancement after contrast is variable. It may be intense but usually less than that seen with meningioma. Fifty percent of patients presenting with the adult form of optic nerve glioma will have optic nerve and chiasmatic involvement.6 These patients usually die within a year of the diagnosis. The prognosis of childhood optic nerve glioma is no different in NF compared to those without (15 year survival was 81% and 76% respectively, not
0009-9260/$ - see front matter q 2005 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2004.05.018
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Orbital compartments, contents and pathology
Compartment
Contents
Pathology
Extraconal
Fat, lacrimal gland, bony orbit
Conal
Muscles
Intraconal
Fat, lymph nodes, vessels, nerves, optic nervesheath complex
Infection, neurofibroma, adenocarcinoma, mucoepidermoid, adenoid cystic carcinoma, carcinoma: primary (benign/malignant)/ secondary, neoplasia of bone, lymphoma Rhabdomyosarcoma, thyroid eye disease, idiopathic orbital inflammation (pseudotumour) Venolymphatic malformation, haemangioma, arteriovenous malformation, optic nerve meningioma/glioma, lymphoma Retinoblastoma, metastasis, melanoma
Globe
significant) despite NF patients having a longer mean time to tumour progression (8.37 years vs. 2.39 years).7,8 This is controversial and other authors have suggested that NF1 has a protective effect on patients with chiasmatic gliomas.9 The distribution of involvement differs in the two groups. Patients without NF are more likely to have hypothalamic and/or posterior tract involvement or chiasm involvement alone. There is no difference in distribution between the NF and nonNF group for isolated optic nerve glioma or chiasmatic involvement with one or both optic nerves involved. Meningioma The second most common tumour of the optic nerve sheath complex is meningioma. Distinction should be made between this primary origin as opposed to secondary orbital involvement from an intracranial source such as an intraosseous meningioma involving the greater wing of the sphenoid. These benign tumours arise from arachnoid cells within the leptomeninges. Very rarely, they may arise from arachnoid rest cells inside the orbit. Optic nerve sheath meningiomas constitute 3% of all orbital tumours. They are bilateral in 5% of cases, usually associated with neurofibromatosis type II, radiotherapy or meningiomatosis. Although benign, they are difficult to treat as complete removal along with the dura strips the optic nerve of its blood supply. These difficulties have led to alternative forms of treatment such as stereotactic radiotherapy.10 ONS Meningiomas present with slowly progressive, painless visual impairment with or without proptosis and optic atrophy. The central visual field is characteristically preserved for many years. Middle-aged women are most commonly affected. The tumour characteristically involves the ONS complex in a continuous rather than segmental fashion producing a fusiform (Fig. 4) or tubular
enlargement of the ONS, but globoid eccentric tumours are well recognized. This feature may help distinguish meningioma from schwannoma, which arises eccentrically, although meningiomas arising at the orbital apex may have a similar appearance. Meningioma may show calcification on CT and enhances uniformly after contrast administration producing a tramtrack sign (Fig. 4)11 due to the enveloped non-enhancing and attenuated optic nerve. The MRI equivalent is the doughnut sign on the coronal image. The sign is not specific and has variably been described in optic neuritis and idiopathic orbital inflammation (pseudotumour)12, 13 involvement. There may be hyperostosis (Fig. 4) and optic canal widening (Fig. 5)14 or narrowing usually associated with secondary orbital involvement and intracanalicular optic nerve spread respectively.15 MRI demonstrates a similar configuration with isointensity to the optic nerve on T1 and T2 although it may be low signal on T1 and high signal on T2. Fat saturated, contrast enhanced T1weighted images provide best lesion demonstration. In contradistinction to optic nerve glioma where the optic nerve is expanded, it may be compressed by the more intensely enhancing meningioma (Fig. 5). A cystic component may be identified between the tumour and the globe due to focal sheath dilatation (capping cyst) and has once been described as the cause of acute onset proptosis in this condition.16 Optic neuritis There are several causes of optic neuritis with multiple sclerosis being one of the most common. Seventy five percent of patients with multiple sclerosis will have involvement of the eye in the course of their illness.17 In 35% of patients with multiple sclerosis, visual dysfunction is the presenting feature with internuclear ophthalmoplegia developing in 35–50% of cases.18 Presentation is with reduced visual acuity over days with pain on
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eye movement and an afferent papillary defect. The mechanism is a T cell mediated response against myelin antigen. The aetiology is uncertain but is presumably related to genetic and ethnic factors and geographical location, with a greater incidence further away from the equator. MRI is the principle modality for the investigation of clinically suspected multiple sclerosis and provides paraclinical support for the diagnosis.19 Orbital findings include optic nerve enlargement in the acute stage with plaques of T2-weighted hyperintensity and localised or diffuse enhancement (Fig. 6). Intracranial demyelination may also be evident. Atrophy is present in the chronic stage. The length and position of lesions may have prognostic significance with long and intracanalicular lesions having a worse prognosis.20 Fat saturated imaging, which can be achieved by two means (STIR and SPIR—see part 1, technique), eliminate high signal from surrounding fat improving sensitivity.21 However, high signal within the CSF from increased T2-w and image distortion from magnetic field inhomogeneity complicate each sequence respectively. Combined water and fat suppression techniques (FLAIR/SPIR—see part 1, technique) are reported as further improving lesion detection by suppressing the CSF within the optic nerve sheath.22 Imaging specifically to look at the optic nerve where there is clinical certainty about the diagnosis of MS is unhelpful as only extremely rarely are there other causes for symptoms.23 Vascular tumours Refer to haemangiomas that should be distinguished from lymphangioma, venous-lymphatic malformations and arteriovenous malformations.24,25 These lesions have typical locations but may involve more than one compartment. Haemangioma and lymphangioma are discussed under the extraconal section. Venous lymphatic malformations Is a spectrum from predominantly venous malformations to lymphatic malformations (Fig. 7). Cavernous haemangioma (Fig. 8) is a misnomer used to describe a venous malformation that is usually intraconal but may be intraosseous and therefore extraconal. They present between 10 and 40 years of age with progressive enlargement Figure 1 (a)–(c). Axial T1-weighted unenhanced scan (a) showing isointense tubular thickening of the orbital segment of the left optic nerve (short black arrows), which is hyperintense on the T2-weighted coronal fat saturated sequence (b curved arrow). The affected segment of the nerve shows avid enhancement (c black !).
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resulting in proptosis and diplopia. Increased growth may occur during pregnancy or after trauma. They are well-defined (due to a fibrous pseudocapsule) ovoid lesions26 usually sparing the orbital apex. They rarely involve the globe but may result in remodelling of the orbital bone, consistent with a slow-growing benign lesion. Cavernous haemangiomas are usually low signal on T1weighted and increased on T2-weighted MRI with variable enhancement.27 The enhancement pattern is similar on CT and precontrast these lesions are hyperdense. Varix There is controversy as to whether this pathology is part of the lymphangioma spectrum or a discrete entity.28 The majority opinion is that it is a discrete entity. A varix is a dilated vein or group of veins that present with intermittent proptosis aggravated by increased intracranial pressure caused by the Valsalva manoeuvre or postural change due to their continuity with the systemic circulation in the majority of cases. They are of uncertain aetiology but theories include arteriovenous shunts and thrombosis. On imaging tubular masses are identified which may increase in size if the scans are acquired before and after Valsalva. The veins usually taper towards the apex and reveal no internal septation. Varices may show hyperdensity on CT precontrast and an absence of flow void in the context of thrombosis. Calcified phleboliths are pathognomonic if present (Fig. 9). There is an association with non-contiguous intracranial venous malformations in approximately 10% of cases and therefore investigations should include an assessment of the intracranial veins.29
Muscle cone
Figure 2 (a, b). On this axial T2-weighted image (a) there is fusiform thickening of the orbital segment of the left optic nerve and perineural spread (solid black arrow), the thickened sheath being markedly hyperintense. The posterior globe is flattened and proptosed (black !). The axial T1-weighted post-contrast image (b) shows avid enhancement of tumour and sheath within the orbit (short black arrow), but also sheath enhancement within the optic canal (long black arrow).
Pseudotumour (idiopathic orbital inflammation) Pseudotumour is characterised histologically by an inflammatory infiltrate of predominantly mature lymphocytes, plasma cells and macrophages and less commonly by a granulomatous infiltrate, desmoplasia and eosinophilia.30 Rarely multinucleated giant cells and non-caseating granuloma formation is present. The diagnosis is made after the exclusion of other pathologies including Wegener’s granulomatosis, sarcoid, systemic lupus erythematosis, polyarteritis nodosa, rheumatoid, Sjo ¨grens, lymphoproliferative disorders, metastasis and Erdheim-Chester. 31 Associated disorders include fibrosing mediastinitis, retroperitoneal
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Figure 4 (a, b). Two patients with bilateral tubular optic nerve sheath meningiomas. The axial post contrast CT shows tram-track hyperdensity (short black arrow) of the sheath enclosing an attenuated hypodense optic nerve (a). There is hyperostosis of the left anterior clinoid process (curved black arrow). (b) An axial post-contrast T1-weighted MRI shows clear evidence of early intracranial meningeal spread around the anterior clinoid processes (long black arrow) and planum sphenoidale (curved black arrow), which was not evident on the axial CT.
Figure 3 (a–c). Globoid expansion and enhancement of the left optic nerve within the orbit is shown on this T1weighted axial enhanced image (a), with an area of cystic change anteriorly behind the globe (long black arrow). Thickening and enhancement of the sheath is also present (short black arrow), although sheath and nerve appear to
be separated by a hypointense capsule (b) (black arrowhead) which does not enhance in (a). There is evidence of intracranial extension with cystic change within the affected left side of the chiasm on a coronal T2-weighted image (curved black arrow) (c).
Orbital imaging: Part 2. Intraorbital pathology
Figure 5 (a, b). A hyperintense fusiform intracanalicular optic nerve sheath meningioma protrudes into the orbital apex (black short arrow), on this axial T2weighted fat saturated image (a). Anterior to the tumour the optic nerve sheath is distended (black o), and the optic nerve itself is atrophic (long black arrow). The optic canal is widened. Enhancement of the meningioma is avid (black m) (b).
and hepatic fibrosis, Riedel’s thyroiditis and cholangitis. Any age group may be affected with adults in the 4th to 6th decade predominating. Unilateral involvement occurs in 85% of adults, but is more frequent in children.32 There is a spectrum of disease based on speed of onset, location and
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Figure 6 (a–c). Axial (a) and coronal (b) contrastenhanced CT and coronal fat-saturated post-contrast T1weighted MRI (c). There is diffuse enlargement of the right optic nerve sheath complex (black o) with enhancement.
extent of involvement. Inflammation may present acutely, subacutely or in a slowly progressive or chronic form. Disease may present in the anterior structures (periscleritis, sclerotendinitis, uveitis), within the lacrimal gland (lacrimal adenitis), within the apex (apicitis), diffusely (diffuse orbital inflammation), within the extraocular muscle (myositis) and involving the optic nerve (perineuritis). The disease process may spread intracranially to involve the cavernous sinus, infratemporal fossa as well as into the nasopharynx via the pterygopalatine fossa.33,34 The sclerosing form is thought to be a
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Figure 8 Enhanced axial CT of a cavernous haemangioma. There is a well-defined triangular shaped, retrobulbar intraconal and heterogeneously enhancing lesion (white *) splaying the rectus muscles (black arrow) and causing proptosis. The appearances are typical of a ‘cavernous haemangioma’.
Figure 9 Axial post contrast CT showing an ovoid intraconal and extraconal mass within the left orbit, with some areas of reduced enhancement (long black arrow). There is proptosis of the globe, and the numerous intralesional calcified phleboliths (short black arrow) are pathognomonic of varices. Figure 7 (a–c). Axial post contrast CT showing a welldefined right intra-conal mass anteromedially within the orbit, displacing and flattening the globe (short black arrow) (a). (b) The axial T2-weighted MRI shows the mass to be relatively hyperintense (curved arrow). (c) T1weighted image demonstrates focal areas of hyperintensity consistent with methaemoglobin (solid black arrow). Histology was that of a venolymphatic malformation.
subtype of orbital pseudotumour and presents in a chronic progressive form that is resistant to treatment. The presentation is determined by the above factors and range from acute onset of painful exophthalmos with adjacent features of inflammation (uveitis, scleritis) to cranial nerve involvement, painful ophthalmoplegia and forehead numbness due to III, IV, VI and V1 involvement in the cavernous sinus (Tolosa Hunt). Children have constitutional symptoms in 14% leading, erroneously, to the diagnosis of orbital cellulitis. The
Orbital imaging: Part 2. Intraorbital pathology
Figure 10 Orbital pseudotumour. Contrast enhanced orbital CT. There is diffuse infiltration of the right medial rectus (black r) with blurring of its edges due to involvement of the adjacent intra- and extra-conal fat. There is proptosis with preseptal soft tissue (short black arrow) and scleral thickening (long black arrow) and flattening of the posterolateral globe.
diagnosis is assisted by imaging features, which alone are non-specific. One or many of the following features may be present. There is focal or diffuse soft tissue within the orbit that enhances after contrast. The fat is infiltrated and streaky (dirty fat). Proptosis usually occurs (except in the sclerosing type) and there is extraocular muscle involvement with enlarged muscles with blurred edges due to adjacent fat involvement (Fig. 10). Muscle tendons as well as the optic nerve may be enlarged. The lacrimal gland is the most frequently involved orbital structure. There is diffuse glandular involvement with spilling over of the inflamma-
Figure 11 Axial CT showing diffuse infiltration of the orbit by a soft tissue mass filling intraconal and extraconal compartments, with resultant flattening of the proptosed globe (thick black arrow). The left ethmoid air cells (curved black arrow) and anterior clinoid process (black c) are less well pneumatised. The lamina papyracea and lateral orbital bony margin appear sclerotic (short black arrows).
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tory process to the surrounding tissues, most commonly the lateral rectus, resulting in an indistinct border. Bone erosion is rare but remodelling may occur. Bone sclerosis occurs in 17% of cases presumed to be due to a low-grade osteitis usually associated with the sclerosing subset (Fig. 11). The infiltrate is hypointense to fat on T1 and isointense on T2 which does help to distinguish pseudotumour from tumour although other aetiologies such as sarcoid may have similar signal. Proliferating cell nuclear antigen (PCNA), a marker of nuclear protein in dividing cells will not be elevated in pseudotumour or low grade lymphoma compared with increased titres in high grade lymphoma. Furthermore, the B cell to T cell ratio is increased in lymphoid tumours and together with the PCNA are useful adjuncts to clinical and imaging features. Treatment is with steroids with dramatic response that is helpful in confirming the diagnosis. The sclerosing type responds poorly. Lymphoma has also been shown to respond in a similar way and this has been used as an argument against the prevailing opinion as to the usefulness of oral steroids.35 Thyroid eye disease Is the most common disorder affecting the orbit, usually presenting in middle age women. The orbitopathy may precede thyroid disease or occur with euthyroid or hypothyroidism, but is most common in the context of Graves’ disease. There is usually an acute presentation with exacerbations and remissions becoming chronic over months to years.36 Patients with known Graves’ disease may have asymptomatic myopathy in up to 71% of cases.37 The acute phase may simulate an orbital cellulitis clinically with injection, chemosis and lid swelling. In the chronic phase proptosis, diplopia due to a restrictive myopathy and lid lag are demonstrated. Pain is not usually a feature until late, a distinguishing feature from inflammatory pseudotumour. Inflammation is immune mediated and histologically there is an inflammatory infiltrate of lymphocytes and plasma cells predominantly with the production of hyaluronic acid, a mucopolysaccharide that is deposited within the extraocular muscles resulting in fibrosis. No eosinophil infiltration or lymphoid follicle formation occur as may be the case in idiopathic inflammation. The inferior rectus is most often involved followed by the medial rectus and superior muscle complex. There is a strong tendency to bilaterality. Isolated lateral rectus involvement is rare and should prompt consideration of alternative diagnoses (idiopathic inflammation, myositis, lymphoma, metastasis). There
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Figure 12 (a–c) Axial and coronal CT after contrast administration in two different patients with Grave’s ophthalmopathy. (a, b) There is fusiform, symmetrical enlargement of the medial rectus muscle (black r) and to a lesser degree the lateral rectus muscle (black l). The tendons are spared producing a ‘bottle neck’ appearance (long black arrow). There is bilateral proptosis. No inflammatory change is present within the fat. The crowding of the orbital apex is best appreciated on the coronal image (b). (c) Contrast enhanced coronal view of the orbit demonstrating diffuse inflammatory changes within the orbital fat (black f). (d) Fat saturated coronal T2-weighted and gadolinium enhanced T1-weighted images. There is diffuse extraocular muscle enhancement with lesser involvement of the lateral rectus. Illdefined signal hyperintensity is present within the orbital fat above the inferior rectus (short black arrow). (e) After gadolinium, there is diffuse enhancement of the extraocular muscles and the orbital fat.
is a strong association between smoking and the risk and severity of developing orbitopathy in Graves’ disease. Radiologically, there is increase in the volume of orbital fat, which is a non-specific sign also seen in obesity. The fat is initially unaffected (Fig. 12(a)
and (b)). Enlarged muscles produce apical crowding and venous congestion. The inflammatory response spills over into the intraorbital fat and together produce streaking within the fat (‘dirty fat’) (Fig. 12(c)). The muscles are usually involved bilaterally with a fusiform appearance due to characteristic
Orbital imaging: Part 2. Intraorbital pathology
Figure 13 Axial (a) and coronal T2-weighted (b) images showing a lobulated largely hyperintense extraconal mass superiorly within the right orbit consistent with a neurofibroma of the frontal nerve (black n). There is thinning of the orbital roof locally due to pressure remodelling (thick black arrow). Note the enlargement of the ipsilateral extra-ocular muscles due to thyroid eye disease.
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optic nerve sheath complex may also be enlarged and the superior ophthalmic vein congested. The delicate lamina papyracea may be moulded by the muscle enlargement. These imaging features are efficiently diagnosed and monitored with CT, especially acquired in the coronal plane, with the exception of apical crowding which is more readily assessed on coronal MRI. MRI (Fig. 12(d) and (e)) may be used to predict the response to therapy by distinguishing between muscle inflammation and fibrosis on the basis of T2-weighted relaxation time.38 A fat saturated T2 sequence is particularly good for this application. Similarly using the same criteria, MRI has been used to monitor response to therapy. The natural history of thyroid eye disease is that approximately 20% of patients will require a surgical procedure with the average time to surgery being 3.3 year.39 The vast majority require supportive medical or no treatment. Corticosteroids produce improvement in symptoms in up to 60% of patients within 24–72 h, but relapse occurs after dose reduction. The amount of disease activity predicts the response to therapy. Side effects are common restricting their long-term use. Other treatments include orbital irradiation40 and decompression performed for optic neuropathy, optic nerve compression, medically refractory disease and exposure keratopathy. Imaging plays an important role in distinguishing causes of muscle enlargement in combination with clinical features. Tendinous involvement is more suggestive of pseudotumour, although the absence of this sign does not exclude pseudotumour. Graves’ is more frequently bilateral than pseudotumour and often symmetric. Pseudotumour results in blurred muscle edges whereas initially in thyroid disease these are distinct. Pain is uncommon in thyroid ophthalmopathy as opposed to pseudotumour. Metastases tend to be more localized and nodular and lymphoma tends to cause greater muscle enlargement over a longer timecourse and can respond to steroids. Lacrimal gland involvement is common in lymphoma and pseudotumour but is rare in thyroid disease (although may occur).
Extraconal space sparing of the muscle tendons. Inflammation is initially limited to the muscle, which therefore has a crisp well-defined border in distinction to pseudotumour. The combination of extraocular muscle enlargement and increase intraorbital fat produces proptosis. Optic nerve compression due to apical crowding is rare (!10%), but results clinically in decreased visual acuity and fields. The retro-orbital
Schwannoma/neurofibroma Schwannoma and neurofibroma share similar appearances and nerve involvement and are considered jointly. Schwannoma is more common and comprises up to 6% of orbital masses.41 Both tumours are benign and slow growing presenting more commonly in the adult
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Figure 14 (a, b) Axial enhanced orbital CT and surface shaded 3D CT. (a) There is a heterogeneous orbital mass occupying both intra- and extra-conal spaces extending anteriorly into the preseptal soft tissues and posteriorly into the cavernous sinus (black c), middle cranial fossa (where a fleck of calcification is present, black long arrow) and cerebellopontine angle cistern. There is widening of the superior orbital fissure (curved black arrow (b), remodelling of the lamina papyracea (short black arrow) and ethmoid air cells. There is dysplasia of the greater wing of sphenoid (black s) with temporal bossing producing enlargement of the middle cranial fossa subarachnoid space. Note the presence of a further plexiform neurofibroma overlying the ipsilateral temporal fossa (black t) and the widened optic nerve canal (solid black arrow (b)) secondary to an optic nerve glioma in this patient with neurofibromatosis 1.
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Figure 15 (a–c). (a, b) Pre- and post-contrast orbital CT in a young male infant with a capillary haemangioma. There is an extraconal lobulated enhancing mass lesion located in the superomedial quadrant occupying the pre and post septal position (black h). The globe is displaced inferolaterally. (c) Coronal fat saturated T2-weighted scan (different patient) demonstrates a hyperintense lobulated extraconal mass with flow voids (black arrows) consistent with a haemangioma.
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Figure 16 Venolymphatic malformation with features of lymphatic malformation. Unenhanced, axial CT mid orbits. There is a well-defined intraconal cystic lesion with fluid-fluid levels (short black arrows) displacing the globe anteriorly and the optic nerve sheath complex medially (long black arrow).
population except in the context of neurofibromatosis. The most commonly affected nerves are the sensory branches of V1 accounting for their position in the superior orbit (Fig. 13).42 Painless proptosis is the mode of presentation. Imaging depends on histological characteristics for schwannomas with Antoni A lesions being more uniform than Antoni B tumours. They are usually hypointense on T1-w and hyperintense on T2-w. Both enhance with contrast. The benign nature of these lesions may lead to expansion of the orbit and bone remodelling. Plexiform neurofibromata (Fig. 14) are associated with hypoplasia of the greater wing of the sphenoid and macrophthalmia in neurofibromatosis type I. Neurofibromata may be distinguished by the presence of calcification that is rarely seen in schwannomas. The optic nerve may be displaced or involved. Haemangioma Capillary haemangiomas (Fig. 15) differ in clinical presentation, location and age of presentation. Capillary haemangioma is usually extraconal, situated in the upper medial (superomedial) quadrant with associated cutaneous malformations over the face. They are present at birth, grow rapidly in the first year of life and regress usually by 7 to 10 years of age.25 They are less well defined than the socalled cavernous haemangiomas (venous malformations). They more commonly arise extraconally and anteriorly, but may infiltrate posteriorly to involve the orbital apex and extend intracranially
through the superior orbital fissure or optic canal. Intraconal extension also occurs. Flow voids may be identified within and on the surface of capillary haemangiomas on T2-weighted images, which is a helpful distinguishing feature from lymphangioma. A prominent arterial supply is usually demonstrable from either the external or the internal carotid circulation. The signal intensity is determined by the amount of fibrosis, calcification and haemosiderin deposition after haemorrhage. The appearance prior to delayed scans may be indistinguishable from neurofibroma, schwannoma and haemangiopericytoma. Venous lymphatic malformations Lymphatic malformation comprises a network of bloodless spaces lined by flattened poorly supported endothelial cells lying in a loose stroma of lymphoid tissue and small blood vessels. This explains the propensity for sudden increase in size due to haemorrhage or viral infection.43 Imaging demonstrates a lobular, infiltrating extraconal mass that may remodel the orbit. Density and signal depend on the presence of haemorrhage that may also cause fluid-fluid levels (Fig. 16). Calcification is rare. Flow voids are absent which helps distinction from capillary haemangioma. Rim enhancement may occur after contrast administration. These lesions can be treated with good success with Sodium tetradecylsulphate injection44 Lymphoma Lymphoma
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Figure 17 (a–d) Manifestations of orbital lymphoma. (a) Unenhanced axial CT with well-defined homogenous unilateral lesion (white *) centred on the lacrimal gland with thinning of the adjacent lateral orbital wall (white arrow). The lesion displaces the globe but the shape of the lesion conforms to its outline (black arrows). (b) A well-defined, uniformly enhancing, intraconal, retrobulbar mass (white *) and additional lacrimal involvement (black *). (c), (d) Infiltrating lymphoma involving intraconal and conal compartments, cavernous sinus, masticator space and temporal fossa. There is an ill-defined, uniformly enhancing mass infiltrating rectus muscles (white arrowhead) and extending posteriorly through the superior orbital fissure into the anterior cavernous sinus (black arrow). There is preseptal and temporal fossa soft tissue thickening (white *). Coronal images reveal extension through the inferior orbital fissure (white circle) into the masticator space (black arrowhead), infraorbital canal (white arrowhead) and suprazygomatic temporal fossa (white *).
lymphoproliferative disease affects the superolateral orbital quadrant with the lacrimal gland being most commonly affected (Fig. 17(a)). Any compartment, however, may be affected although primary involvement of the extraocular muscles is rare. Lymphoma accounts for 10–15% of orbital masses. Seventy-five percent of patients with orbital lymphoma will eventually have systemic disease, usually non-Hodgkin’s lymphoma (NHL). One percent of patients will have orbital involvement during the course of their illness45 but presentation with orbital involvement is rare.
Presentation is usually in adults in the sixth to seventh decade46 and women are more commonly affected. Painless downward proptosis is therefore the most common mode of presentation.47 The imaging findings are numerous with a spectrum of a well-defined mass lesion (Fig. 17(b)) to the more common ill-defined infiltration (Fig. 17(c) and (d)).48 The tumour is conformable to the surroundings structures and bone erosion or sclerosis is uncommon. CT characteristically displays a dense mass. The signal characteristics are determined by cell
Orbital imaging: Part 2. Intraorbital pathology
Figure 18 Axial contrast enhanced CT showing diffuse infiltration of the intraconal and extra-conal compartments by soft tissue, from metastatic scirrhous carcinoma of the breast. This results in bilateral enophthalmos. The fibrous form of idiopathic orbital inflammation could have similar appearances.
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Figure 20 Enhanced axial CT in a young child with partially treated neuroblastoma metastases. There is an enhancing soft tissue mass (compared with unenhanced brain imaging-not shown) centred on the greater wing of sphenoid projecting anteromedially into the extraconal space (with deviation of the lateral rectus muscle (short black arrow)) and into the middle cranial and temporal fossa (long black arrow). The bone has a permeative pattern with a central lytic component. Dural enhancement is seen along the anterior middle cranial fossa (curved black arrow).
Figure 19 (a, b). Contrast enhanced axial CT of orbit and brain with biopsy proven lacrimal and brain melanoma metastasis. (a) There is an irregular, enhancing (when compared with unenhanced head imaging-not shown) lobulated soft tissue density of the right lacrimal gland (short black arrow) in association with (b) a left frontoparietal intra-axial lesion with surrounding vasogenic oedema (long black arrow). There is gradation of density within the brain lesion suggesting haemorrhage (curved black arrow).
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Figure 22 (a, b). (a) Enhanced axial CT and (b) Axial T2 weighted MRI (different patients) adenoid cystic carcinoma. (a) There is a heterogeneous partly calcified lesion (black *) arising from the lacrimal gland invading the adjacent greater wing of sphenoid and orbital plate of the zygoma (white *) with anteromedial globe displacement. (b) Different patient demonstrating mixed signal with cystic component (black *) lying posterior to a calcific focus (white arrow) embedded in isointense tumour. No bone destruction. Figure 21 (a) Axial CT and (b, c) T2- and enhanced T1weighted MRI (different patient) pleomorphic adenoma. There is a well-circumscribed oval lesion (white *) arising from the orbital lobe of the lacrimal gland with scalloping of the adjacent orbital margin (black arrow) and inferomedial globe displacement. No calcification or sclerosis. (b) The lesion is heterogeneously isointense rather than hyperintense, (c) and enhances avidly (black *).
packing and may be low on T1 and T2 weighted images where there is dense packing or high on T2 where packing is less dense. Contrast enhancement is variable. Bilateral orbital masses should raise the suspicion of lymphoma. Lymphoma may have appearances identical to idiopathic orbital
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inflammation. Increased proliferating cell nuclear antigen (PCNA) and an increased B cell to T cell ratio may be useful discriminators.49 NHL of the orbit responds to both chemotherapy and radiotherapy. Miller demonstrated that patients with unfavourable histology receiving both treatments did better than those receiving chemotherapy alone.50 Radiotherapy alone is effective for localised histologically more favourable subtypes of lymphoma. Metastases and extraorbital malignancy Common primary sources for orbital metastases include breast (Fig. 18), lung, stomach, thyroid, renal carcinoma and melanoma (Fig. 19). The orbit is a common site for neuroblastoma metastasis in childhood (Fig. 20). Involvement is usually extraconal involving the retrobulbar fat, orbital bone and the lacrimal gland, although the conal muscles are primarily involved in less than 10% of cases.51 Schirrous breast metastasis produce enophthalmos that may mimic idiopathic orbital inflammation (Fig. 18). Painful proptosis is the most common presentation except when the metastasis is a scirrhous breast metastasis when enophthalmos occurs. The orbit may be involved from extension of malignancy from the sinuses, nasopharynx and globe. Tumour is often irregular and poorly defined with signal intensity similar to muscle and variable enhancement. Melanoma may demonstrate hyperdensity on CT. Simultaneous brain metastases are seen in two thirds of patients with orbital metastases.
Figure 23 (a–c) Axial and coronal orbital CT after contrast administration in two different patients. (a) There is preseptal soft tissue thickening (solid black arrow) and oedema extending posteriorly to involve the temporal muscle (curved black arrow) secondary to orbital cellulitis. No postseptal extension. The cavernous sinus and superior ophthalmic vein (not shown) were patent. (b, c) There is an intraorbital abscess with a thin enhancing wall within the superior (curved black arrow) and medial extraconal space. The globe is proptosed and displaced inferolaterally. A focal defect is present within the lamina papyracea with opacification of the ipsilateral frontal recess and ethmoid sinuses (short black arrow). No intracranial extension was present.
Lacrimal gland Pathology affecting the lacrimal gland should be divided into two groups based on the clinical history and examination. The first group are the primary benign neoplasms of epithelial origin accounting for 50% of epithelial origin tumours. These present with progressive, painless swelling without radiologically sinister features of invasion. One such tumour the pleomorphic adenoma (Fig. 21) should not be biopsied due to local seeding, but should be excised completely.52 These tumours are distinguished by their contour and the appearance of the lacrimal fossa.53,54 They are well-defined lesions that involve the orbital surface of the lacrimal gland (with or without posterior extension) and mould the surrounding bone without destruction although occasionally one may see sclerosis. The second group includes the other 50% of epithelial tumours, which are malignant, including adenoid cystic (Fig. 22) or mucoepidermoid carcinoma, metastasis, lymphoproliferative disease (primary
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or secondary) and inflammatory processes such as idiopathic inflammation of the orbit and Wegener’s. Here the history is shorter, there may be pain and radiologically sinister features may be present. Imaging is non-specific. Key features helping in the diagnosis include the presence of pain in association with a firm mass in a young patient with the peak age being the 4th decade. The malignant epithelial lesions have a less well-defined or serrated border and there is a propensity to early infiltration along nerves with satellite lesions. Pressure erosion of the lacrimal fossa is common and bone erosion is occasionally seen. Calcification is more common in malignancy than pleomorphic adenoma. 55 Mucoepidermoid carcinoma may be hyperintense on T1. Lymphoma and pseudotumour are discussed elsewhere but mould to the surrounding structures and infiltrate the gland in its entirety (including the palpebral lobe) in contradistinction to epithelial tumours. The lacrimal gland is amenable to biopsy, which is often the method of diagnosis except where a pleomorphic adenoma is suspected clinically based on the features discussed above.
Figure 24 (a–c). (a, b) Enhanced axial CT (soft tissue and bone windows) and (c) T1-weighted gadolinium enhanced images of a dermoid. (a) There is a 2 cm well defined fat density (*) lying adjacent to the orbital surface of the zygomatic bone extending more superiorly (b) into a corticated bone defect (white arrow). (c) Increased signal consistent with fat was demonstrated both pre- (not shown) and post gadolinium although difficult to make out without fat saturation due to inflammatory changes post dermoid rupture (black arrow).
Infection The orbit may be involved in infection from the sinuses, face, less commonly from dental disease, via haematogenous spread, and direct trauma with or without foreign body penetration. Infection is usually caused by Staphylococcus or Streptococcus. The spread of infection from the paranasal sinuses may occur by direct penetration of the thin-walled lamina papyracea, which does not constitute a significant barrier to infection. Alternatively, infection may spread through the numerous communicating venous channels or diploic veins of Breschet. The periosteum of the orbit or periorbita is a tough layer which is loosely attached to much of the orbit except at the optic canal, superior orbital and inferior orbital fissure where it fuses with the dura and anteriorly to the orbital rim and lacrimal sac fossa. Anteriorly it also contributes to the orbital septum thus forming a formidable barrier to spread of infection from the preseptal region (Fig. 23(a)). Fusion with the dura implies a continuous potential space between the subperiosteal space and the epidural space explaining the complication of extradural brain abscess. Intracranial spread of infection may also progress to meningitis, subdural or parenchymal abscess. Venous drainage from the angular vein of the face through superior and inferior ophthalmic veins allows
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spread of infection intracranially and potentially into the masticator space through their communications with the cavernous sinus and pterygoid plexus. Thrombosis of these venous confluences may also occur. Imaging features vary according to the stage of progression of infection originally described by Chandler and modified by Lemke.56 An important distinction between an orbital phlegmon and a subperiosteal abscess can be made. In the former, there is heterogeneous increased tissue along the orbital wall with fat replacement and tissue within the subperiosteal space. In abscess formation, a medical and surgical emergency, there is increased intraocular pressure due to infective subperiosteal material that forms a ring-enhancing lesion (Fig. 23(b) and (c)) that may have an air fluid level within it, displacing the medial rectus muscle. Adjacent paranasal sinus disease is usual. There may be osteomyelitis of adjacent orbital bone. Treatment is with intravenous antibiotics and surgical drainage. Harris examined the size and radiodensity of subperiosteal abscesses in 37 patients less than 9 years of age. He noted an increase in the size of the abscess during the initial few days of antibiotic treatment. The increase in size had no effect on outcome.57 He found the initial CT scan was not predictive of the patient’s clinical course and advised medical treatment only unless there was an indication for surgical intervention such as impaired vision and intracranial infection.
Figure 25 (a–c). Axial CT images from two patients with histologically proven orbital amyloid. In image (a) there is enlargement of the left lacrimal gland (long black arrow). The anterolateral right orbital mass (b and c) contains foci of dystrophic calcification (short black arrow) within it but also within the temporal fossa. There is sclerosis of the zygoma (black z).
Dermoid cyst The sequestration of ectodermal components within the developing orbital bone usually occurs along the superolateral orbital margin at the zygomaticofrontal suture although the frontoethmoidal suture, superomedially, is the next most common site. Dermoid cysts are the most common congenital lesions of the orbit. They are well-defined slow growing lesions lying within the extraconal space and have local mass effect on the bone with erosion and remodelling. Occasionally presentation may be acute after rupture (Fig. 24), simulating an acute inflammation. MRI demonstrates a lesion with hyperintensity on T1 closely applied to the overlying bone with a tail of tissue extending into the bone. If the secretory elements predominate within the dermoid, the lesion may have signal characteristics similar to epidermoids. There may be a fat-fluid levels and calcification. Very occasionally, rim enhancement is seen if contrast is administered.
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Amyloid The orbit may be involved with primary or less commonly secondary amyloid. Deposition of B pleated proteinaceous sheets occurs in the upper eyelid, lacrimal gland and extraocular muscles. Enlargement occurs and calcification is not uncommon (Fig. 25). The signal intensity on MRI is governed by the presence of calcium, which renders the tissue hypointense, otherwise in the absence of calcification the tissue resembles muscle on all sequences.
Conclusion We have presented a pictorial review of common intraorbital lesions using a compartmental approach. We acknowledge that several pathological processes may involve more than one space, but we have attempted to classify pathologies under the most common presenting compartment. Knowledge of the contents of each compartment provides a cue for the differential diagnosis in each compartment.
Acknowledgements Dr G Quaghebeur for review of an early manuscript and useful suggestions.
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