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Review of orbital imaging
European Journal of Radiology 66 (2008) 387–395
Review
Review of orbital imaging P.S. Goh a,∗ , M.T. Gi a , A. Charlton b , C. Tan c , J.K. Gangadhara Sundar c , S. Amrith c a
Department of Diagnostic Imaging, National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074, Singapore b Department of Pathology, National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074, Singapore c Department of Ophthalmology, National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074, Singapore Received 23 March 2008; received in revised form 24 March 2008; accepted 28 March 2008
Abstract CT and MRI are commonly used in the evaluation of patients with suspected orbital disease. Many different diseases may present within this small anatomical space. The purpose of this article is to present a diagnostic strategy based on a compartment model. Localizing pathology to sinus, bone, extraconal space, muscle cone, intraconal space, optic nerve, globe or lacrimal fossa allows significant reduction in the number of differential diagnoses as these compartments contain different tissues which disease may involve or arise from. Certain diseases may also present in multiple compartments. Common diseases which might present in one or multiple compartments will be discussed. © 2008 Elsevier Ireland Ltd. All rights reserved. Keywords: Orbital imaging; Infection; Mucocoele; Fibrous Dysplasia; Meningioma; Metastases; Fractures; Navigation Guided Surgery; Orbital Inflammatory Disease; Thyroid Eye Disease; Lymphoma; Optic Nerve Glioma; Retinoblastoma; Capillary Haemangioma; Cavernous Haemangioma; Rhabdomyosarcoma; Caroticocavernous Fistula; Dermoid
Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Diagnostic strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sinus and bone disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Muscle cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optic nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The globe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intraconal masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extraconal masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The lacrimal compartment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The anterior compartment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Diagnostic strategy There are several approaches to the diagnosis of orbital pathology in use. A common strategy is to localize the pathology to one of the defined compartments of the orbit. These have been described as the muscle cone, formed by the four rectus muscles, dividing the orbit into intraconal and extraconal com-
∗
Corresponding author. E-mail address: [email protected] (P.S. Goh).
0720-048X/$ – see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejrad.2008.03.031
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partments, with the optic nerve within the central part of the muscle cone, and the extraocular muscles forming separate compartments. The extraconal compartment is bordered by the bony orbit and subperiosteal compartment. The lacrimal gland and globe form the other compartments. The optic canal forms the apex of the pyramidal orbit, and the orbital septum the base of the orbit anteriorly, with the lids forming the anterior or preseptal compartment [1,2]. Recently, some authors have attempted to further refine this framework by using anatomical location, bone and sinus involvement, content, shape and associated features to increase diagnostic specificity [3]. In this article, we will
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Fig. 1. Orbital infection. (a) Axial contrast-enhanced CT scan shows right lid swelling and extent of preseptal inflammatory swelling in periorbital cellulitis (arrow). (b) Axial contrast-enhanced CT scan showing left anterior ethmoid sinusitis with subperiosteal abscess in medial left orbit (arrow).
Fig. 2. Frontoethmoid mucocoeles. (a) Axial contrast-enhanced CT scan showing frontoethmoid mucocoele presenting as orbital mass (asterisk). (b) Coronal contrast-enhanced CT scan showing frontoethmoid mucocoele presenting as orbital mass (asterisk).
examine common diseases affecting each compartment, as well as several with multicompartment or transcompartmental presentation. We will review the bone and sinus compartment first, then muscle cone, the optic nerve, the globe, followed by the
intraconal and extraconal compartments, lacrimal gland fossa and anterior compartment to discuss typical diseases involving these compartments. Examples of transcompartmental disease will also be discussed.
Fig. 3. Fibrous dysplasia. (a) Axial bone window CT scan shows bony expansion of the left ethmoid and sphenoid sinus (asterisk) as well as left greater wing sphenoid. There is secondary mass effect on left optic nerve. (b) Axial T2-weighted MRI image shows bony expansion of the left ethmoid and sphenoid sinus (asterisk) as well as left greater wing sphenoid. There is secondary mass effect on the left optic nerve.
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Fig. 4. Meningioma. (a) Coronal bone window CT scan shows hyperostosis of left greater wing sphenoid bone with orbital apex involvement (arrow). (b) Axial contrast-enhanced CT scan shows hyperostosis of left greater wing sphenoid bone with secondary compression on left optic nerve (arrow). (c) Axial T1-weighted contrast-enhanced MRI image shows bilateral perineural extension into both optic canals (arrows). (d) Sagittal T1-weighted contrast-enhanced MRI image shows perineural extension into optic canal (arrow).
2. Sinus and bone disease The presence of sinus or bone disease is a key feature to identify in patients with extraconal disease. These commonly extend into the extraconal space. Sinusitis and tumours are the most common diseases involving the bones and sinuses. Orbital imaging to exclude bone and soft tissue injuries from orbital trauma is also commonly performed.
The spectrum of sinusitis commonly includes mucosal thickening of the paranasal sinuses, with eventual opacification of the sinuses, air fluid levels within the sinuses and expansion of the sinuses with variable amount of bony dehiscence with mucocoele formation. Orbital infections may originate from skin and eyelid disease, or be related to sinusitis. In the former, preseptal swelling is often seen, with intraorbital involvement later (Fig. 1a). Sinusitis may be complicated by subperiosteal abscess
Fig. 5. Metastatic cancer. (a) Coronal contrast-enhanced T1-weighted MRI image of patient with metastatic breast carcinoma to skull vault, clivus and left greater wing sphenoid giving rise to left proptosis (asterisk). (b) Axial T2-weighted MRI image of patient with metastatic breast carcinoma to left globe (arrow).
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Fig. 6. Orbital fractures. (a) Coronal non-contrast-enhanced CT scan shows a depressed floor of orbit fracture with teardrop appearance of inferior rectus muscle indicating likely muscle entrapment (arrow). (b) Oblique sagittal bone window CT scan shows a depressed floor of orbit fracture (arrow). (c) Coronal bone window CT scan shows comminuted orbital fractures surrounding left optic canal with potential optic nerve impingement (arrow).
formation, and intraorbital extraconal inflammatory collections (Fig. 1b). Progression to cavernous sinus thrombosis, meningitis or sudden visual loss may occur [4]. CT and MRI are the main imaging modalities [5]. Chronic infection may result in mucocoeles which may present as orbital mass lesions with proptosis. These most commonly occur in the frontoethmoid sinuses [6] (Fig. 2a and b). Clinical presentation of pain, fever and systemic features of an infectious process usually allow definitive diagnosis together with radiological findings. Masses involving the bones and sinuses may be due to certain tumour like conditions like fibrous dysplasia, primary tumours like meningiomas, or metastatic disease commonly from breast, prostate and lung.
Fibrous dysplasia commonly presents with sinus expansion. Fibrous dysplasia most commonly involves the frontal or sphenoid bone. It characteristically produces expansion of the bone shown as prominent calcified bone density material on CT. Due to fibrous stroma and osteoid material, it typically shows low T1 and T2 signal on MR with enhancement after gadolinium [7]. The bone expansion may lead to foraminal narrowing and impingement of the optic nerve (Fig. 3a and b). Bony expansion may also be related to tumours. Meningiomas may arise either primarily from the optic nerve sheath or periosteum of the orbital wall, or secondarily from the sphenoid ridge or tuberculum sellae and extend into the orbit. They comprise approximately one third of primary optic nerve tumours
Fig. 7. Thyroid eye disease. (a) Coronal contrast-enhanced CT scan shows typical enlargement of the inferior and medial recti bilaterally (arrow). (b) Coronal contrast-enhanced T1-weighted MRI image shows hypertrophy of the left rectus muscles with secondary compression of the left optic nerve at the orbital apex (arrow).
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Fig. 8. Orbital inflammatory disease. (a) Coronal contrast-enhanced CT scan showing infiltrative soft tissue mass in right orbit with loss of normal tissue planes (arrow). (b) Axial contrast-enhanced CT scan showing orbital pseudotumour presenting as left lacrimal fossa mass (arrow).
and more commonly present in middle aged females. Bilateral meningiomas are seen in neurofibromatosis. Secondary meningiomas present with hyperostosis and expansion of the bones adjacent to the orbit. Primary meningiomas typically have a perineural location with enhancing tissue surrounding optic nerve [8]. Presence of calcification helps confirm diagnosis. Secondary meningiomas may present with visual impairment secondary to compression of the optic nerve (Fig. 4a–d). Orbital metastases most commonly arise from breast, prostate and lung. Common sites are to the bones of the skull base and orbit with metastases to the globe being much less common [9]. Contrast-enhanced CT and MRI are useful in demonstrating intracranial and orbital involvement (Fig. 5a and b) Trauma may result in disruption of bony continuity of the orbital walls, together with soft tissue swelling and haematomas. CT is the procedure of choice in evaluating patients with orbital trauma. It is a rapid test that can detect bony and soft tissue injury, haemorrhage and foreign bodies. CT is also able to quickly evaluate other injuries in the rest of the body, in many of these patients who may be unstable, or in whom physical examination is difficult [10]. Trauma may be blunt, penetrating or involve implantation of foreign bodies. The classical injury seen in blunt trauma is the blowout fracture. This commonly involves the floor and medial wall of the orbit [11]. Features which indicate likely extraocular muscle entrapment include muscle prolapse, and a “tear drop” shape pointing toward the fracture, indicating muscle sheath tethering. A suggestive finding which should raise suspicion of a blowout fracture is the presence of orbital emphysema. Eval-
uation for involvement of the optic canal, and bone fragments in the vicinity of the optic nerve should be made. In the era of navigational surgery, thin section axial, coronal and oblique sagittal reformatted images not only help diagnosis but treatment planning and navigation guided surgery (Fig. 6a–c). 3. Muscle cone The muscle cone is composed of the extraocular muscles along with interconnecting intermuscular septa. This forms a natural separation between the intraconal and extraconal compartments. Common diseases involve enlargement or infiltration of the extraocular muscles. Infiltration may be inflammatory in nature, or related to tumours. Enlargement of the extraocular muscles is one of the common presentations of thyroid eye disease. Graves’ disease is an autoimmune disorder associated with excess thyroid gland secretion. Thyroid eye disease is the most common cause of unilateral and bilateral proptosis in adults. It is four times more common in women and peaks in the fourth and fifth decades. Imaging features are typically enlargement of the extraocular muscles with inferior and medial recti most commonly involved (75%), followed by superior and lateral recti (50%) (Fig. 7a and b). Typically there is sparing of the tendinous portion of the muscle. Other diagnoses should be considered with isolated rectus involvement. Sagittal imaging with CT or MRI is useful to visualize the entire length of the superior and inferior recti [12]. The other common cause of proptosis in Graves’ disease is an increase in the amount of intraorbital fat.
Fig. 9. Orbital lymphoma. (a) Axial contrast-enhanced CT scan shows preseptal mass (arrow). (b) Coronal contrast-enhanced CT scan shows tumour infiltrate in both lacrimal glands (arrow).
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The other common cause of muscle enlargement is orbital inflammatory disease or orbital pseudotumour. This can be distinguished from thyroid eye disease by involvement of the tendinous portion of the extraocular muscles, as well as the adjacent soft tissues surrounding the muscles in the intraconal or extraconal space. Orbital inflammatory disease or orbital pseudotumour is one of the most common causes of an intraorbital mass. It is one of the most common causes of unilateral exophthalmos, with bilateral disease also common. The typical clinical triad is a patient with proptosis, pain and impaired ocular movement. Age of presentation ranges from 10 to 40 years commonly. Typical radiological findings are contrast enhancing uveal–scleral thickening. This may be isodense to slightly hyperdense on CT with moderate enhancement. Involvement of the rectus muscles, obliteration of retrobulbar soft tissue planes, lacrimal gland, or optic nerve sheath may occur mimicking optic nerve sheath meningioma [13,14] (Fig. 8a and b). Common tumours which may present with enlargement of the extraocular muscles include lymphoma and metastatic disease. Lymphoma may present with unilateral or bilateral disease, and manifest in the orbit as the primary site or as part of systemic disease. It may present in any compartment, including isolated extraocular muscle enlargement, though lacrimal gland involvement with clinical manifestation of lid swelling and a palpable mass is most common [15]. It may mimic orbital inflammatory disease A more diffuse form with infiltration of the intraconal and extraconal space with effacement of normal tissue planes may occur. On CT it appears commonly as a hyperdense contrast enhancing mass (Fig. 9a and b). Metastatic disease may also present with isolated extraocular muscle involvement. Commonest primary tumours are breast and lung carcinoma. Typically involvement of other sites, e.g. skull, lungs, etc. or history of known primary carcinoma is helpful in making diagnosis.
Fig. 10. Metastatic cancer. Axial contrast-enhanced T1-weighted MRI scan shows thickening and enhancement of both optic nerve sheaths, more on the left side (arrow), due to metastatic colonic cancer. Leptomeningeal tumour also depicted over cerebellar vermis and surrounding brainstem.
4. Optic nerve The optic nerve and globe form the innermost tissues of the orbit. The optic nerve is part of the central nervous system during embryological development and the optic nerve sheath is part of the meninges. The most common primary tumour of the optic nerve is the optic nerve glioma. The most common primary tumour arising from the optic nerve sheath is a meningioma. Differential diagnosis of optic nerve sheath thickening is metastatic disease. On CT and MRI, meningiomas can typically be visualized separately from the optic nerve, giving rise to a “tram-track appearance”. Similar appearance may occur with optic nerve sheath metastases (Fig. 10). Optic nerve gliomas also occur in children, while meningiomas and metastatic disease typically occurs in adults. Optic nerve gliomas are typically intraconal masses inseparable from the optic nerve. These tumours commonly present in children with 50% less than 5 years of age. They may be unilateral or bilateral. They have well-defined margins. Calcification is rare in absence of previous radiotherapy. There is no orbital hyperostosis unlike meningioma. Heterogeneous enhancement is related to mucin deposits which appear as mottled lucent areas (Fig. 11). A widened optic canal occurs in up to 90% and is
Fig. 11. Optic nerve glioma. Axial non-contrast-enhanced T1-weighted MRI scan shows intraconal tumour in right orbit expanding optic nerve and extending through optic canal into suprasellar space (arrows).
more common than with meningioma. Bilateral disease strongly suggests neurofibromatosis [16]. Meningiomas and metastatic disease have been described previously. 5. The globe The commonest primary malignant tumour which arises from the retina is the retinoblastoma. This is a tumour of childhood. In adults, metastatic disease may present with a retinal mass. Retinoblastomas are tumours arising from the retina. They usually occur in children younger than 5 years of age and may be
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Fig. 12. Retinoblastoma. Axial T2-weighted MRI image shows intraocular tumour involving posterior vitreous (arrow).
hereditary or nonhereditary. They may present with leukocoria in about half of patients. It is the most common primary intraocular tumour of childhood. Typical findings on non-contrast CT are speckled calcification. MR is useful for evaluating extraocular and intracranial disease [17] (Fig. 12). 6. Intraconal masses The intraconal space lies within the muscle cone and outside the optic nerve sheath with the globe anteriorly and optic canal posteriorly. The space contains fat, vessels and nerves primarily. Dilated vessels associated with caroticocavernous fistulas, and primary vascular tumours like the capillary and cavernous haemangioma can occur in this space. Infiltration from multicompartmental processes like orbital inflammatory disease or lymphoma may also occur. Enlargement of the ocular muscles associated with thyroid eye disease or rhabdomyosarcoma may also narrow the intraconal space. Caroticocavernous fistula may be traumatic or occur spontaneously. They represent a communication between the internal carotid artery and the cavernous sinus. They may be slow flow or high flow, the determination of which affects therapy [18]. CT or MR angiography may be used, though catheter angiography offers the option of endovascular treatment. Classical findings
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Fig. 14. Capillary haemangioma. Contrast-enhanced T1-weighted axial MRI image shows enhancing tumour in extraconal and intraconal compartment (asterisks).
on CT or MRI are enlargement of the ipsilateral cavernous sinus and a distended ipsilateral superior ophthalmic vein (Fig. 13a and b). Capillary haemangioma is a common intraconal tumour. This is the most common childhood benign orbital tumour, is more common in females, appears within first 2 weeks post-partum, is non-encapsulated, and may be very large. The tumour has irregular margins with prominent enhancement and may be difficult to distinguish from rhabdomyosarcoma [19] (Fig. 14). Cavernous haemangioma is the most common benign intraorbital lesions in adults and most commonly presents in the second to fifth decades. They typically present with painless slowly progressive proptosis and are mostly intraconal. They have smooth margins, are homogeneous in density, show uniform enhancement and are easily separated from the optic nerve and extraocular muscles [19] (Fig. 15a and b). 7. Extraconal masses The extraconal space lies between the orbital muscle cone and the periosteum of the bony orbit. It contains mainly fat, some vessels and nerves. Infection or orbital inflammatory dis-
Fig. 13. Caroticocavernous fistula. (a) Axial contrast-enhanced CT scan shows bulky right cavernous sinus (arrow). (b) Coronal contrast-enhanced CT scan shows distended right superior ophthalmic vein (arrow).
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Fig. 15. Cavernous haemangioma. (a) Axial contrast-enhanced CT scan shows a well-defined spherical intraconal enhancing mass (arrow). (b) Axial contrast-enhanced T1-weighted MRI image shows the well-defined enhancing intraconal tumour (arrow).
ease may present with mass-like infiltration of this space. Sinus and bone disease as well as muscle pathology discussed previously can encroach upon this space. These have been discussed previously. Rhabdomyosarcoma is a common extraconal mass in childhood. Rhabdomyosarcomas are the most common mesenchymal childhood tumours. Incidence peaks at approximately 5–10 years of age. These tumours may present with rapid proptosis. CT shows a mass similar in density to muscle with irregular margins with most in the extraconal space though half have intraconal extension. These are aggressive tumours with bone erosion and intracranial extension seen [20]. On MRI, these tumours are usually hypointense to muscle on T1, hyperintense on T2 and show relatively uniform enhancement (Fig. 16a and b). 8. The lacrimal compartment The lacrimal gland occupies this space and may be involved in inflammatory, infiltrative or neoplastic processes [21]. These may be present as bilateral or unilateral masses. Lymphoma or
orbital inflammatory disease may present as unilateral or bilateral masses. The commonest benign neoplasm of the lacrimal gland is the pleomorphic adenoma. The most common primary malignant neoplasm is the adenocystic carcinoma though this is rare. Lacrimal gland enlargement may also be seen in systemic disease like sarcoidosis. 9. The anterior compartment The anterior compartment or periorbital space may be involved in diffuse infiltrative processes like periorbital cellulitis, orbital inflammatory disease, lymphoma or rhabdomyosarcoma as discussed previously. Discrete masses may also be localized here like the external angular dermoid. External angular dermoids are the most common congenital childhood masses. They typically present superolaterally adjacent to the orbital rim. These tumours are slow growing and appear as well-defined non-enhancing low-density lesions on CT. Bony erosion may occur related to their slow growth [22] (Fig. 17).
Fig. 16. Orbital rhabdomyosarcoma. (a) Coronal contrast-enhanced T1-weighted MRI image shows enhancing superior extraconal and preseptal bulky tumour (asterisk). (b) Axial contrast-enhanced T1-weighted MRI image shows enhancing extraconal and preseptal tumour (asterisk).
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Fig. 17. Orbital dermoid. Axial contrast-enhanced CT scan shows well-defined fat density mass and remodeling of the adjacent bone (arrow).
10. Conclusion A systematic evaluation using an anatomical compartment strategy, evaluation of imaging features, as well as correlation with clinical presentation and patient age is useful in the diagnosis of patients with orbital disease. Useful features on CT are density including calcification and contrast enhancement, and on MRI the signal characteristics of the mass and contrast enhancement. References [1] Bloching M, Beck R, Knipping S, Mir-Salim PA, Duncker GI, Berghaus A. Orbital space-occupying lesions. Practical aspects of imaging. HNO 2001;49(1):21–8. [2] Wichmann W, Muller-Forell W. Anatomy of the visual system. Eur J Radiol 2004;49(1):8–30. [3] Ben Simon GJ, Annunziata CC, Fink J, Villablanca P, McCann JD, Goldberg RA. Rethinking orbital imaging. Establishing guidelines for interpreting orbital imaging studies and evaluating their predictive value in patients with orbital tumours. Ophthalmology 2005;112(12):2196– 207.
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Review
Review of orbital imaging P.S. Goh a,∗ , M.T. Gi a , A. Charlton b , C. Tan c , J.K. Gangadhara Sundar c , S. Amrith c a
Department of Diagnostic Imaging, National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074, Singapore b Department of Pathology, National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074, Singapore c Department of Ophthalmology, National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074, Singapore Received 23 March 2008; received in revised form 24 March 2008; accepted 28 March 2008
Abstract CT and MRI are commonly used in the evaluation of patients with suspected orbital disease. Many different diseases may present within this small anatomical space. The purpose of this article is to present a diagnostic strategy based on a compartment model. Localizing pathology to sinus, bone, extraconal space, muscle cone, intraconal space, optic nerve, globe or lacrimal fossa allows significant reduction in the number of differential diagnoses as these compartments contain different tissues which disease may involve or arise from. Certain diseases may also present in multiple compartments. Common diseases which might present in one or multiple compartments will be discussed. © 2008 Elsevier Ireland Ltd. All rights reserved. Keywords: Orbital imaging; Infection; Mucocoele; Fibrous Dysplasia; Meningioma; Metastases; Fractures; Navigation Guided Surgery; Orbital Inflammatory Disease; Thyroid Eye Disease; Lymphoma; Optic Nerve Glioma; Retinoblastoma; Capillary Haemangioma; Cavernous Haemangioma; Rhabdomyosarcoma; Caroticocavernous Fistula; Dermoid
Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Diagnostic strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sinus and bone disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Muscle cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Optic nerve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The globe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intraconal masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extraconal masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The lacrimal compartment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The anterior compartment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Diagnostic strategy There are several approaches to the diagnosis of orbital pathology in use. A common strategy is to localize the pathology to one of the defined compartments of the orbit. These have been described as the muscle cone, formed by the four rectus muscles, dividing the orbit into intraconal and extraconal com-
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Corresponding author. E-mail address: [email protected] (P.S. Goh).
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partments, with the optic nerve within the central part of the muscle cone, and the extraocular muscles forming separate compartments. The extraconal compartment is bordered by the bony orbit and subperiosteal compartment. The lacrimal gland and globe form the other compartments. The optic canal forms the apex of the pyramidal orbit, and the orbital septum the base of the orbit anteriorly, with the lids forming the anterior or preseptal compartment [1,2]. Recently, some authors have attempted to further refine this framework by using anatomical location, bone and sinus involvement, content, shape and associated features to increase diagnostic specificity [3]. In this article, we will
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Fig. 1. Orbital infection. (a) Axial contrast-enhanced CT scan shows right lid swelling and extent of preseptal inflammatory swelling in periorbital cellulitis (arrow). (b) Axial contrast-enhanced CT scan showing left anterior ethmoid sinusitis with subperiosteal abscess in medial left orbit (arrow).
Fig. 2. Frontoethmoid mucocoeles. (a) Axial contrast-enhanced CT scan showing frontoethmoid mucocoele presenting as orbital mass (asterisk). (b) Coronal contrast-enhanced CT scan showing frontoethmoid mucocoele presenting as orbital mass (asterisk).
examine common diseases affecting each compartment, as well as several with multicompartment or transcompartmental presentation. We will review the bone and sinus compartment first, then muscle cone, the optic nerve, the globe, followed by the
intraconal and extraconal compartments, lacrimal gland fossa and anterior compartment to discuss typical diseases involving these compartments. Examples of transcompartmental disease will also be discussed.
Fig. 3. Fibrous dysplasia. (a) Axial bone window CT scan shows bony expansion of the left ethmoid and sphenoid sinus (asterisk) as well as left greater wing sphenoid. There is secondary mass effect on left optic nerve. (b) Axial T2-weighted MRI image shows bony expansion of the left ethmoid and sphenoid sinus (asterisk) as well as left greater wing sphenoid. There is secondary mass effect on the left optic nerve.
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Fig. 4. Meningioma. (a) Coronal bone window CT scan shows hyperostosis of left greater wing sphenoid bone with orbital apex involvement (arrow). (b) Axial contrast-enhanced CT scan shows hyperostosis of left greater wing sphenoid bone with secondary compression on left optic nerve (arrow). (c) Axial T1-weighted contrast-enhanced MRI image shows bilateral perineural extension into both optic canals (arrows). (d) Sagittal T1-weighted contrast-enhanced MRI image shows perineural extension into optic canal (arrow).
2. Sinus and bone disease The presence of sinus or bone disease is a key feature to identify in patients with extraconal disease. These commonly extend into the extraconal space. Sinusitis and tumours are the most common diseases involving the bones and sinuses. Orbital imaging to exclude bone and soft tissue injuries from orbital trauma is also commonly performed.
The spectrum of sinusitis commonly includes mucosal thickening of the paranasal sinuses, with eventual opacification of the sinuses, air fluid levels within the sinuses and expansion of the sinuses with variable amount of bony dehiscence with mucocoele formation. Orbital infections may originate from skin and eyelid disease, or be related to sinusitis. In the former, preseptal swelling is often seen, with intraorbital involvement later (Fig. 1a). Sinusitis may be complicated by subperiosteal abscess
Fig. 5. Metastatic cancer. (a) Coronal contrast-enhanced T1-weighted MRI image of patient with metastatic breast carcinoma to skull vault, clivus and left greater wing sphenoid giving rise to left proptosis (asterisk). (b) Axial T2-weighted MRI image of patient with metastatic breast carcinoma to left globe (arrow).
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Fig. 6. Orbital fractures. (a) Coronal non-contrast-enhanced CT scan shows a depressed floor of orbit fracture with teardrop appearance of inferior rectus muscle indicating likely muscle entrapment (arrow). (b) Oblique sagittal bone window CT scan shows a depressed floor of orbit fracture (arrow). (c) Coronal bone window CT scan shows comminuted orbital fractures surrounding left optic canal with potential optic nerve impingement (arrow).
formation, and intraorbital extraconal inflammatory collections (Fig. 1b). Progression to cavernous sinus thrombosis, meningitis or sudden visual loss may occur [4]. CT and MRI are the main imaging modalities [5]. Chronic infection may result in mucocoeles which may present as orbital mass lesions with proptosis. These most commonly occur in the frontoethmoid sinuses [6] (Fig. 2a and b). Clinical presentation of pain, fever and systemic features of an infectious process usually allow definitive diagnosis together with radiological findings. Masses involving the bones and sinuses may be due to certain tumour like conditions like fibrous dysplasia, primary tumours like meningiomas, or metastatic disease commonly from breast, prostate and lung.
Fibrous dysplasia commonly presents with sinus expansion. Fibrous dysplasia most commonly involves the frontal or sphenoid bone. It characteristically produces expansion of the bone shown as prominent calcified bone density material on CT. Due to fibrous stroma and osteoid material, it typically shows low T1 and T2 signal on MR with enhancement after gadolinium [7]. The bone expansion may lead to foraminal narrowing and impingement of the optic nerve (Fig. 3a and b). Bony expansion may also be related to tumours. Meningiomas may arise either primarily from the optic nerve sheath or periosteum of the orbital wall, or secondarily from the sphenoid ridge or tuberculum sellae and extend into the orbit. They comprise approximately one third of primary optic nerve tumours
Fig. 7. Thyroid eye disease. (a) Coronal contrast-enhanced CT scan shows typical enlargement of the inferior and medial recti bilaterally (arrow). (b) Coronal contrast-enhanced T1-weighted MRI image shows hypertrophy of the left rectus muscles with secondary compression of the left optic nerve at the orbital apex (arrow).
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Fig. 8. Orbital inflammatory disease. (a) Coronal contrast-enhanced CT scan showing infiltrative soft tissue mass in right orbit with loss of normal tissue planes (arrow). (b) Axial contrast-enhanced CT scan showing orbital pseudotumour presenting as left lacrimal fossa mass (arrow).
and more commonly present in middle aged females. Bilateral meningiomas are seen in neurofibromatosis. Secondary meningiomas present with hyperostosis and expansion of the bones adjacent to the orbit. Primary meningiomas typically have a perineural location with enhancing tissue surrounding optic nerve [8]. Presence of calcification helps confirm diagnosis. Secondary meningiomas may present with visual impairment secondary to compression of the optic nerve (Fig. 4a–d). Orbital metastases most commonly arise from breast, prostate and lung. Common sites are to the bones of the skull base and orbit with metastases to the globe being much less common [9]. Contrast-enhanced CT and MRI are useful in demonstrating intracranial and orbital involvement (Fig. 5a and b) Trauma may result in disruption of bony continuity of the orbital walls, together with soft tissue swelling and haematomas. CT is the procedure of choice in evaluating patients with orbital trauma. It is a rapid test that can detect bony and soft tissue injury, haemorrhage and foreign bodies. CT is also able to quickly evaluate other injuries in the rest of the body, in many of these patients who may be unstable, or in whom physical examination is difficult [10]. Trauma may be blunt, penetrating or involve implantation of foreign bodies. The classical injury seen in blunt trauma is the blowout fracture. This commonly involves the floor and medial wall of the orbit [11]. Features which indicate likely extraocular muscle entrapment include muscle prolapse, and a “tear drop” shape pointing toward the fracture, indicating muscle sheath tethering. A suggestive finding which should raise suspicion of a blowout fracture is the presence of orbital emphysema. Eval-
uation for involvement of the optic canal, and bone fragments in the vicinity of the optic nerve should be made. In the era of navigational surgery, thin section axial, coronal and oblique sagittal reformatted images not only help diagnosis but treatment planning and navigation guided surgery (Fig. 6a–c). 3. Muscle cone The muscle cone is composed of the extraocular muscles along with interconnecting intermuscular septa. This forms a natural separation between the intraconal and extraconal compartments. Common diseases involve enlargement or infiltration of the extraocular muscles. Infiltration may be inflammatory in nature, or related to tumours. Enlargement of the extraocular muscles is one of the common presentations of thyroid eye disease. Graves’ disease is an autoimmune disorder associated with excess thyroid gland secretion. Thyroid eye disease is the most common cause of unilateral and bilateral proptosis in adults. It is four times more common in women and peaks in the fourth and fifth decades. Imaging features are typically enlargement of the extraocular muscles with inferior and medial recti most commonly involved (75%), followed by superior and lateral recti (50%) (Fig. 7a and b). Typically there is sparing of the tendinous portion of the muscle. Other diagnoses should be considered with isolated rectus involvement. Sagittal imaging with CT or MRI is useful to visualize the entire length of the superior and inferior recti [12]. The other common cause of proptosis in Graves’ disease is an increase in the amount of intraorbital fat.
Fig. 9. Orbital lymphoma. (a) Axial contrast-enhanced CT scan shows preseptal mass (arrow). (b) Coronal contrast-enhanced CT scan shows tumour infiltrate in both lacrimal glands (arrow).
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The other common cause of muscle enlargement is orbital inflammatory disease or orbital pseudotumour. This can be distinguished from thyroid eye disease by involvement of the tendinous portion of the extraocular muscles, as well as the adjacent soft tissues surrounding the muscles in the intraconal or extraconal space. Orbital inflammatory disease or orbital pseudotumour is one of the most common causes of an intraorbital mass. It is one of the most common causes of unilateral exophthalmos, with bilateral disease also common. The typical clinical triad is a patient with proptosis, pain and impaired ocular movement. Age of presentation ranges from 10 to 40 years commonly. Typical radiological findings are contrast enhancing uveal–scleral thickening. This may be isodense to slightly hyperdense on CT with moderate enhancement. Involvement of the rectus muscles, obliteration of retrobulbar soft tissue planes, lacrimal gland, or optic nerve sheath may occur mimicking optic nerve sheath meningioma [13,14] (Fig. 8a and b). Common tumours which may present with enlargement of the extraocular muscles include lymphoma and metastatic disease. Lymphoma may present with unilateral or bilateral disease, and manifest in the orbit as the primary site or as part of systemic disease. It may present in any compartment, including isolated extraocular muscle enlargement, though lacrimal gland involvement with clinical manifestation of lid swelling and a palpable mass is most common [15]. It may mimic orbital inflammatory disease A more diffuse form with infiltration of the intraconal and extraconal space with effacement of normal tissue planes may occur. On CT it appears commonly as a hyperdense contrast enhancing mass (Fig. 9a and b). Metastatic disease may also present with isolated extraocular muscle involvement. Commonest primary tumours are breast and lung carcinoma. Typically involvement of other sites, e.g. skull, lungs, etc. or history of known primary carcinoma is helpful in making diagnosis.
Fig. 10. Metastatic cancer. Axial contrast-enhanced T1-weighted MRI scan shows thickening and enhancement of both optic nerve sheaths, more on the left side (arrow), due to metastatic colonic cancer. Leptomeningeal tumour also depicted over cerebellar vermis and surrounding brainstem.
4. Optic nerve The optic nerve and globe form the innermost tissues of the orbit. The optic nerve is part of the central nervous system during embryological development and the optic nerve sheath is part of the meninges. The most common primary tumour of the optic nerve is the optic nerve glioma. The most common primary tumour arising from the optic nerve sheath is a meningioma. Differential diagnosis of optic nerve sheath thickening is metastatic disease. On CT and MRI, meningiomas can typically be visualized separately from the optic nerve, giving rise to a “tram-track appearance”. Similar appearance may occur with optic nerve sheath metastases (Fig. 10). Optic nerve gliomas also occur in children, while meningiomas and metastatic disease typically occurs in adults. Optic nerve gliomas are typically intraconal masses inseparable from the optic nerve. These tumours commonly present in children with 50% less than 5 years of age. They may be unilateral or bilateral. They have well-defined margins. Calcification is rare in absence of previous radiotherapy. There is no orbital hyperostosis unlike meningioma. Heterogeneous enhancement is related to mucin deposits which appear as mottled lucent areas (Fig. 11). A widened optic canal occurs in up to 90% and is
Fig. 11. Optic nerve glioma. Axial non-contrast-enhanced T1-weighted MRI scan shows intraconal tumour in right orbit expanding optic nerve and extending through optic canal into suprasellar space (arrows).
more common than with meningioma. Bilateral disease strongly suggests neurofibromatosis [16]. Meningiomas and metastatic disease have been described previously. 5. The globe The commonest primary malignant tumour which arises from the retina is the retinoblastoma. This is a tumour of childhood. In adults, metastatic disease may present with a retinal mass. Retinoblastomas are tumours arising from the retina. They usually occur in children younger than 5 years of age and may be
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Fig. 12. Retinoblastoma. Axial T2-weighted MRI image shows intraocular tumour involving posterior vitreous (arrow).
hereditary or nonhereditary. They may present with leukocoria in about half of patients. It is the most common primary intraocular tumour of childhood. Typical findings on non-contrast CT are speckled calcification. MR is useful for evaluating extraocular and intracranial disease [17] (Fig. 12). 6. Intraconal masses The intraconal space lies within the muscle cone and outside the optic nerve sheath with the globe anteriorly and optic canal posteriorly. The space contains fat, vessels and nerves primarily. Dilated vessels associated with caroticocavernous fistulas, and primary vascular tumours like the capillary and cavernous haemangioma can occur in this space. Infiltration from multicompartmental processes like orbital inflammatory disease or lymphoma may also occur. Enlargement of the ocular muscles associated with thyroid eye disease or rhabdomyosarcoma may also narrow the intraconal space. Caroticocavernous fistula may be traumatic or occur spontaneously. They represent a communication between the internal carotid artery and the cavernous sinus. They may be slow flow or high flow, the determination of which affects therapy [18]. CT or MR angiography may be used, though catheter angiography offers the option of endovascular treatment. Classical findings
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Fig. 14. Capillary haemangioma. Contrast-enhanced T1-weighted axial MRI image shows enhancing tumour in extraconal and intraconal compartment (asterisks).
on CT or MRI are enlargement of the ipsilateral cavernous sinus and a distended ipsilateral superior ophthalmic vein (Fig. 13a and b). Capillary haemangioma is a common intraconal tumour. This is the most common childhood benign orbital tumour, is more common in females, appears within first 2 weeks post-partum, is non-encapsulated, and may be very large. The tumour has irregular margins with prominent enhancement and may be difficult to distinguish from rhabdomyosarcoma [19] (Fig. 14). Cavernous haemangioma is the most common benign intraorbital lesions in adults and most commonly presents in the second to fifth decades. They typically present with painless slowly progressive proptosis and are mostly intraconal. They have smooth margins, are homogeneous in density, show uniform enhancement and are easily separated from the optic nerve and extraocular muscles [19] (Fig. 15a and b). 7. Extraconal masses The extraconal space lies between the orbital muscle cone and the periosteum of the bony orbit. It contains mainly fat, some vessels and nerves. Infection or orbital inflammatory dis-
Fig. 13. Caroticocavernous fistula. (a) Axial contrast-enhanced CT scan shows bulky right cavernous sinus (arrow). (b) Coronal contrast-enhanced CT scan shows distended right superior ophthalmic vein (arrow).
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Fig. 15. Cavernous haemangioma. (a) Axial contrast-enhanced CT scan shows a well-defined spherical intraconal enhancing mass (arrow). (b) Axial contrast-enhanced T1-weighted MRI image shows the well-defined enhancing intraconal tumour (arrow).
ease may present with mass-like infiltration of this space. Sinus and bone disease as well as muscle pathology discussed previously can encroach upon this space. These have been discussed previously. Rhabdomyosarcoma is a common extraconal mass in childhood. Rhabdomyosarcomas are the most common mesenchymal childhood tumours. Incidence peaks at approximately 5–10 years of age. These tumours may present with rapid proptosis. CT shows a mass similar in density to muscle with irregular margins with most in the extraconal space though half have intraconal extension. These are aggressive tumours with bone erosion and intracranial extension seen [20]. On MRI, these tumours are usually hypointense to muscle on T1, hyperintense on T2 and show relatively uniform enhancement (Fig. 16a and b). 8. The lacrimal compartment The lacrimal gland occupies this space and may be involved in inflammatory, infiltrative or neoplastic processes [21]. These may be present as bilateral or unilateral masses. Lymphoma or
orbital inflammatory disease may present as unilateral or bilateral masses. The commonest benign neoplasm of the lacrimal gland is the pleomorphic adenoma. The most common primary malignant neoplasm is the adenocystic carcinoma though this is rare. Lacrimal gland enlargement may also be seen in systemic disease like sarcoidosis. 9. The anterior compartment The anterior compartment or periorbital space may be involved in diffuse infiltrative processes like periorbital cellulitis, orbital inflammatory disease, lymphoma or rhabdomyosarcoma as discussed previously. Discrete masses may also be localized here like the external angular dermoid. External angular dermoids are the most common congenital childhood masses. They typically present superolaterally adjacent to the orbital rim. These tumours are slow growing and appear as well-defined non-enhancing low-density lesions on CT. Bony erosion may occur related to their slow growth [22] (Fig. 17).
Fig. 16. Orbital rhabdomyosarcoma. (a) Coronal contrast-enhanced T1-weighted MRI image shows enhancing superior extraconal and preseptal bulky tumour (asterisk). (b) Axial contrast-enhanced T1-weighted MRI image shows enhancing extraconal and preseptal tumour (asterisk).
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Fig. 17. Orbital dermoid. Axial contrast-enhanced CT scan shows well-defined fat density mass and remodeling of the adjacent bone (arrow).
10. Conclusion A systematic evaluation using an anatomical compartment strategy, evaluation of imaging features, as well as correlation with clinical presentation and patient age is useful in the diagnosis of patients with orbital disease. Useful features on CT are density including calcification and contrast enhancement, and on MRI the signal characteristics of the mass and contrast enhancement. References [1] Bloching M, Beck R, Knipping S, Mir-Salim PA, Duncker GI, Berghaus A. Orbital space-occupying lesions. Practical aspects of imaging. HNO 2001;49(1):21–8. [2] Wichmann W, Muller-Forell W. Anatomy of the visual system. Eur J Radiol 2004;49(1):8–30. [3] Ben Simon GJ, Annunziata CC, Fink J, Villablanca P, McCann JD, Goldberg RA. Rethinking orbital imaging. Establishing guidelines for interpreting orbital imaging studies and evaluating their predictive value in patients with orbital tumours. Ophthalmology 2005;112(12):2196– 207.
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