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Intraorbital Cystic Lesions: An Imaging Spectrum
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Intra-orbital Cystic Lesions: An Imaging Spectrum Shivani Pahwa MD, Sanjay Sharma MD, FRCR, J. Das Chandan, Ekta Dhamija, Saurabh Agrawal MS
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Cite this article as: Shivani Pahwa MD, Sanjay Sharma MD, FRCR, J. Das Chandan, Ekta Dhamija, Saurabh Agrawal MS, Intra-orbital Cystic Lesions: An Imaging Spectrum, Curr Probl Diagn Radiol, http://dx.doi.org/10.1067/j.cpradiol.2015.03.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title: Intra-orbital Cystic Lesions: An Imaging Spectrum Category of paper: Review article Authors: 1. Dr Shivani Pahwa, MD Senior Resident, Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India - 110029 E mail: [email protected] Phone: 91-11-26593078 2. Dr Sanjay Sharma, MD, FRCR Professor, Department of Radiodiagnosis RP Centre of Ophthalmic Sciences All India Institute of Medical Sciences, New Delhi, India- 110029. E mail: [email protected] Phone : 91-11-26593053 3. Dr Chandan J Das Assistant Professor, Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India- 110029. 4. Dr Ekta Dhamija Senior Resident, Department of Radiodiagnosis All India Institute of Medical Sciences
New Delhi, India – 110029 E mail: [email protected] 5. Dr Saurabh Agrawal, MS Research Officer, Department of Community Ophthalmology RP Centre of Ophthalmic Sciences All India Institute of Medical Sciences, New Delhi, India- 110029. Corresponding author: Dr Sanjay Sharma, MD, FRCR Department of Radiodiagnosis, AIIMS, New Delhi- 110029, India E mail: [email protected] Phone: 91-11-26593053 Grants received: None Source of funding: None Acknowledgements: None
Abstract Presence of a cyst or a cystic component in an intra-orbital mass often narrows the list of differential diagnoses to specific entities. Such a lesion in the orbit may arise from structures within the orbit, globe, and lacrimal system or from neighboring paranasal sinuses or meninges. Common congenital and developmental lesions encountered within the orbit include dermoids and epidermoids, and infrequently coloboma. Parasitic cysts (cysticercus), orbital abscess, mucocele, and vascular lesions are the most common acquired pathologies giving rise to fluid containing lesions within the orbit. The role of a
radiologist is crucial in expediting the diagnosis of orbital lesions with the help of characteristic imaging features on ultrasound, computed tomography (CT), or MR (magnetic resonance) Imaging. It also helps in identifying complications in others where formulation of an early and effective management strategy is vital for preserving vision. Introduction A cyst is a sac like structure lined by epithelium and containing fluid or semi-solid material. Cysts may be extraocular or rarely intraocular in location. The spectrum of such lesions is wide - it consists of rather easily managed benign lesions such as uncomplicated dermoids and parasitic cysts at one end to more sinister pathologies such as orbital abscesses and cystic malignant tumors on the other. These lesions are encountered across all age groups with varied clinical presentations. An orbital cyst may be an unsightly congenital cystic eye or colobomatous cyst in a neonate which portends a poor visual outcome, a venolymphatic malformation in a young child with an acute and often dramatic presentation, or an insidious, slowly enlarging mucocele presenting with proptosis in an adult 1. A superficial lesion often presents as a subcutaneous mass or nodule, whereas lesions located deep in the orbit may present with visual disturbances, proptosis, squint or signs and symptoms of inflammation2,3. Shields and Shields3 have classified orbital cystic lesions according to the cell of origin (Table 1). Kaufman et al2 proposed a simpler classification based on the etiology (Table 2). They classified cystic lesions of the orbit as congenital, acquired, and those arising from adjacent structures 1, 2 such as paranasal sinuses, brain and meninges. The organ of origin, cyst wall, internal contents and relationship to adjacent structures are well depicted both on CT and MRI. Bony abnormalities are well depicted on CT whereas MRI because of its excellent soft tissue contrast helps characterize the internal contents and wall characteristics of the lesions. However, because of widespread availability and short imaging time, CT often remains the workhorse of orbital imaging. A stepwise approach is useful in arriving at the correct diagnosis of orbital cystic lesions. Step 1: Look at the cyst contents: for presence of fat and calcification; dermoids are fat containing lesions. Step 2: Look at the exact location of the lesion within the orbit: Dermoids are usually located along lines of closure of sutures; orbital varices and colobomatous cysts are intraconal masses. In case of large masses, the epicenter of the lesion is usually the site of origin. Step3: Look at the relationship of the lesion to the globe, paranasal sinuses and floor of anterior cranial fossa. Colobomatous cysts lie adjacent to a microphthalmic eye; a mucocele will usually communicate
with the frontal or ethmoid sinus and meningocele will be associated with defect in the anterior skull base. In the following sections, we discuss the most commonly encountered lesions, their clinical presentation and radiologic features. CONGENITAL AND DEVELOPMENTAL ORBITAL CYSTS Choristoma (Dermoid, Epidermoid and Dermolipoma) A choristoma is defined as benign, disorganized proliferation of histologically normal tissues in an abnormal location4. Dermoid, epidermoid and dermolipoma are choristomas seen in orbit and are among the most common benign orbital tumors of childhood1,5. They arise from embryonic cell rests that get sequestered or implanted along lines of closure of sutures, meninges, or in the diploe, or due to failure of separation of these cell rests from mesoderm or endoderm1. Both dermoid and epidermoid are lined by squamous epithelium, but dermoids also contain cutaneous appendages as hair follicles, sweat and sebaceous glands. Dermoid cysts can also be classified as cutaneous and conjunctival dermoid cysts, which represent 59% of the total. Based on location, they can be classified as superficial or deep. Superficial dermoids are most commonly located along frontozygomatic (60%) and frontolacrimal (25%) sutures4, and present as painless, firm, subcutaneous periorbital masses in infancy or childhood. On imaging, they are seen as well defined, unilocular masses, with fluid or fat density contents, causing scalloping of the adjacent bone (Figure 1). About 15% may contain foci of calcification4. Presence of fat on imaging is pathognomonic. Deep dermoids and epidermoids present later in life as slow growing, discrete, well circumscribed, freely movable, intra-orbital or rarely intra-osseous masses causing proptosis and diplopia or with signs and symptoms of inflammation if they rupture or get infected. They are situated along suture lines, or even at the orbital apex, and may extend into the adjacent bones. Imaging is essential to establish the exact extent of these masses, because these may have dumbbell shaped extensions into the temporal fossa, intracranial cavity, or paranasal sinuses. If a choristoma is complicated by rupture or infection, CT / MRI will reveal an irregular wall, presence of inflammation in adjacent structures (Figure 1c), and irregularity of bony orbital walls. There may be a documented change in the longstanding image appearances. Dermolipomas are composed of mature fat cells with very little epithelial cells. They are located on the outer canthus of the eye beneath the conjunctiva or in the superotemporal epibulbar region and occasionally causes intermittent ocular irritation. These lesions are often non-cystic, and infiltrate into the peribulbar region, lid, and surrounding orbital tissues. When present, these lesions should not be surgically excised. Bilateral dermolipmas are seen in Goldenhaar’s syndrome1
The differential diagnosis for choristomas depends on the location: it may be of lacrimal gland origin for lesions located in the superotemporal quadrant; mucocele and encephalocele for superomedially located masses, and solid orbital tumors for inflamed masses in other locations. Superficial masses are managed by direct excision, whereas deep masses require combined orbital and neurosurgical approaches for removal. Occasionally, fistulization is seen after incomplete removal of orbital dermoid tumors. Hence defining the exact extent of the cystic mass and its relationship to adjacent structures on pre-operative imaging is crucial for management. Conjunctival cysts Conjunctival cysts are sequestrations of conjunctival and caruncular epithelia occurring in the superonasal aspect of the orbit without a bony defect. They are lined by non-keratinizing conjunctival epithelium and may be congenital or traumatic in origin. These are distinguished on the basis of a lack of historical or clinical evidence of trauma. They are most commonly located medially at or behind the caruncle, and may have fat or fluid contents (Figure 3). When large in size, they can cause motility disturbances, pain, or refractive errors6. In a case series of 11 patients, Goldstein et al6 found that larger conjunctival cysts caused mass effect leading to distortion of the globe in 6 patients, and bone remodeling in another 6. Hence imaging is essential when excision is being planned for a large conjunctival cyst; smaller lesions are managed by complete extirpation. Orbital germ cell tumors Orbital germ cell tumors are very rare tumors, with an unknown incidence. Teratomas are benign germ cell tumors that are seen as unilateral, rapidly growing orbital masses in infant girls 2. Primary orbital teratomas are confined to the orbit and are not associated with a bony defect, whereas combined teratomas extend into the periorbital tissues and cranial cavity. They are composed of cells derived from more than one germ layer, and present as large masses that cause diffuse expansion of the orbit and cause massive unilateral proptosis7,8. Vision is threatened by exposure keratopathy of the displaced globe, or due to stretching of the optic nerve. Defects of orbital bones are present in combined teratomas. Orbital yolk cell carcinomas and endodermal sinus tumors are malignant orbital tumors seen in children. On CT or MRI, germ cell tumors are seen as complex solid-cystic masses that cause expansion of the orbit (teratomas) that displace a normally formed globe, and may extend into periorbital structures or cranial cavity (combined teratomas, malignant germ cell tumors)7. Teratomas may have foci of fat and calcification. Teratomas are managed by surgical excision, with an attempt to preserve the globe, optic
nerve and eyelids8. Malignant orbital yolk cell carcinomas and endodermal sinus tumors are managed by chemotherapy and radiotherapy7. Colobomatous cysts and Morning glory anomaly A coloboma is a congenital or acquired fissure or gap in the coats of the eye, which may involve the sclera, choroid, retina, ciliary body, iris, lens or optic nerve head. Congenital colobomas are bilateral in upto 60%3, most commonly situated at the inferonasal quadrant. They result due to failure of closure of the embryonic fissure at the site of invagination of the optic vesicle. A colobomatous cyst is a neuroectoderm-lined mass that protrudes through a coloboma in the wall of a microphthalmic eye to form an orbital cyst which is connected to the globe with a tunnel like connection. The patient presents with a well formed but markedly small eye displaced by the colobomatous cyst, which may occupy the entire orbit (Figure 4). Colobomatous cysts may occur in isolation or in association with chromosomal anomalies and syndromes as Oculocerebrocutaneous syndrome (Dellman’s focal dermal hypoplasia (Goltz’s syndrome), brachiooculofacial syndrome, CHARGE (coloboma of the eye, heart defects, atresia of the choanae, retardation of growth and / or development, genitourinary and ear abnormalities) and VACTERL (vertebral defects, anal atresia, cardiac defects, trachea-esophageal fistula, renal anomalies, and limb abnormalities) syndromes3. On MRI, these cysts are hypointense on T1 weighted images, hyperintense on T2 weighted images, lie adjacent to the globe, are variable in size, but the exact site of communication between the cyst and the globe may not always be depicted on imaging (Figure 5). Excavation of the optic disc head in optic disc coloboma (Morning glory anomaly) is also well depicted on MRI. Congenital cystic eye, congenital microphthalmos and staphyloma must be considered in the differential diagnosis of a colobomatous cyst. Congenital cystic eye A congenital cystic eye is a rare anomaly that arises due to failure of the optic vesicle to differentiate into a globe9. The child presents at birth with a unilateral, unrecognizable eye. On CT or MRI, a large fluid containing, septated lesion is seen within an enlarged bony orbit2 (Figure 6). The contents have signal intensity of fluid (hypointense on T1 and hyperintense on T2 weighted images), as it is filled with serous fluid. A rudimentary optic nerve connected to the cyst may be seen. Documenting the absence of a microphthalmic eye and a well formed optic nerve on imaging is essential to distinguish congenital cystic eye from a colobomatous eye. Histopathology of an excised congenital cystic eye reveals fibrovascular connective tissue, primitive neuroglial elements, and dysplastic retinal cells. The cysts may enlarge with
time due to secretion of fluid by neuroglial cells. Congenital cystic eye is managed by surgical excision to preserve cosmesis. Craniofacial anomalies such as holoprosencepahly, hydrocephalus, cephaloceles, cleft lip and palate, and cardiac anomalies as Tetrology of Fallot have been described in patients with congenital cystic eye10,11. In a child who presents with an indiscernible globe or with a cystic mass in the eye at birth, the following three differentials should be considered: 1. Microphthalmos with colobomatous cyst, 2. Congenital cystic eye, and 3. Cystic germ cell tumor. ACQUIRED ORBITAL CYSTS Lymphangioma Venolymphatic malformations of the orbit are congenital vascular malformations that have a unique combination of clinical, radiologic and histologic features. They are vascular hamartomas that are isolated from systemic circulation4. They arise from venous anlage and are composed of diaphanous, serous filled, thin endothelium lined venous and lymphatic channels in a collagenous stroma. They also contain lymphoid cells which may proliferate with episodes of viral infection causing proptosis. They are classified into four types: superficial, deep, combined and complex4. Imaging is essential for their detection and defining the extent. Superficial lesions are externally visible and involve the conjunctiva or the eyelid only. They can be easily removed if disfiguring. Deep lesions classically present as sudden proptosis and diplopia in a young boys due to hemorrhage, which may be spontaneous or triggered by trivial trauma. Recurrent hemorrhage leads to formation of a blood filled chocolate cyst. Combined lesions have both superficial and deep components. Complex lesions have extensive vascular malformations with facial, intracranial and systemic abnormalities apart from the orbital component12,13. Sonography reveals a poorly outlined, irregular orbital lesion with low internal reflectivity but highly echogenic internal septae. Contrast enhanced CT will demonstrate an ill-defined, unencapsulated, multilocular, infiltrating, cyst like mass, involving extraconal and intraconal spaces, often showing rim like enhancement. It may have hyperdense contents due to presence of hemorrhage. On MRI, the contents show mixed signal intensity contents on T1 and T2 weighted images due to presence of blood degradation products of varying ages (Figures 7, 8). The presence of fluid-fluid levels due to repeated hemorrhage is characteristic14. Almost half of these patients go on to develop compressive optic neuropathy due to recurrent hemorrhages. Management consists of surgical decompression and evacuation of hematic cysts if acute hemorrhage is causing optic neuropathy. However, total excision is usually not possible due to formation of dense
adhesions with surrounding normal orbital tissues. Hemangiomas and pseudotumors should be considered in the differential diagnosis of these lesions. Both hemangiomas and pseudotumors are well defined, solid masses on imaging and show intense contrast enhancement. Orbital varix These are low flow, distensible, congenital venous malformation composed of abnormally large veins with systemic connection, causing intermittent reversible proptosis13.They are the most common cause of spontaneous orbital hemorrhage. Islam et al15 have described that orbital varices are associated with craniofacial anomalies in 4.5% of the patients. These include major midline encepahaloceles, superomedial defects of the orbital wall, and defects of the greater wing of sphenoid. On ultrasound the finding of an anechoic retrobulbar lesion that exhibits intrinsic flow during the Valsalva maneuver is indicative of a varix, and color Doppler imaging may demonstrate a reversal of flow toward the transducer during the Valsalva maneuver. Dynamic contrast enhanced CT done in prone position or while performing Valsalva maneuver is the technique of choice; the lesion may not be apparent on supine scanning. Imaging shows a tortuous, intensely enhancing lesion that increases in size on Valsalva; phleboliths may also be seen (Figure 9). MRI shows a complex signals with blood products. Thrombosis or hemorrhage may occur in a varix following trauma, forming a chocolate cyst. The differential diagnosis would be lymphangioma and cavernous hemangioma. Smaller lesions are managed conservatively by watchful expectancy and periodic follow up. Surgical intervention via orbitotomy is indicated when large varices raise orbital pressure causing functional deficit or intractable pain, and cosmetic disfigurement16. Dacryocele A dacryocele is seen as a painless, slow growing mass formed due to blockage of excretory ducts of lacrimal glands. It is situated at the outer canthus of the eye if due to blockage of the main lacrimal gland, at the medial canthus if due to blockage of the nasolacrimal duct, and in the conjunctival fornices if ducts of accessory glands of Wolfring and Krause are blocked17. The blockage may be congenital (in neonates)18, post traumatic or infective in origin, or it may be caused due to blockage by a slowly growing lacrimal tumor19. Rarely, the epithelium of the cyst may itself transform into a squamous cell carcinoma 20. Clinically, the dacryocele is firm, non tender and is not compressible, the presence of a bluish discoloration and confirmation with imaging studies as ultrasonography, or nasal endoscopy aid in diagnosis. Congenital dacryoceles are commonly associated with intranasal mucoceles, dacryocystitis, and preseptal cellulitis18.
A dacryocele has non-specific imaging appearance and is seen as a well defined, cystic, non-enhancing lesions centered at lacrimal fossa (Figure 10). It is hypointense on T1 and hyperintense on T2 weighted images. Orbital dermoid and epidermoid, lacrimal gland tumors and frontal mucoceles are the important differential diagnosis for masses in this location. Management is firm pressure or probing or endoscopic excision. Epithelial appendage cysts Tiny (<1 cm), cystic lesions may be seen in the eyelids or superficial orbit due to blockage of ducts of the skin appendages (sebaceous glands, sweat glands) or conjunctiva. Chalazion is the most common epithelial appendage cyst in the lids and is caused by the blockage of Meibomian glands. These lesions are best diagnosed clinically. Imaging is not necessary. Optic nerve sheath meningocele Dural ectasia of optic nerve or optic nerve sheath meningocele21 refers to tubular-cystic enlargement of the dural sheath around the optic nerve. It is a rare condition typically seen in middle age. Hayreh et al 22 noted that the perioptic subarachanoid space is narrowest at the cranio-orbital junction, and hence bony malformations of this region could lead to excessive CSF collection in the optic nerve sheath. However, cystic enlargement of optic nerve sheath occurs most commonly secondary to glaucoma or neoplastic apical masses as a meningioma, optic nerve pilocytic astrocytoma, hemangioma, or due to fractures of cranio-orbital junction23,24. Association with neurofibromatosis type 1, von Hippel-Lindau disease, acquired hypermetropia and choroidal folds is also well known. It may also be associated with empty sella and enlarged subarachnoid cisterns2. Its relationship with raised intracranial tension has not been proven and remains a matter of speculation. Garrity et al
21
introduced the term ‘optic nerve sheath meningocele’ in 1990 to describe cases in which
ectasia of the optic nerve sheath was seen in the absence of an orbital apex mass or congenital malformation of the orbital apex. Patients present with slow or rapid onset of visual disturbances and reduced field of vision and headache. CT or MRI reveal a fusiform or saccular dilatation of the duraarachanoid sheath with a relatively normal appearing optic nerve (Figure 11). Optic nerve tumors such as gliomas, meningiomas, and arachnoid cysts involving the optic nerve sheath must be considered as differential diagnosis. Surgical decompression of the optic nerve sheath should be contemplated for patients presenting with rapid visual loss over 3-6 months23,24.
Parasitic cysts: cysticercus cellulosae Cysticercus cellulosae is the larval form of the pork tapeworm, taenia solium, and is the most common intra-orbital parasitic infection seen in endemic areas25. Humans are intermediate hosts and acquire the infection by feco-oral route by ingestion of eggs through contaminated food and water. The disease is more common in children and young adults. The ova develop into larvae in the intestine, reach the portal circulation, and hence forth get disseminated into the body through the systemic circulation. The cysts are most commonly seen in the subcutaneous tissues, muscles, brain and eyes. Extraocular muscles are the most commonly affected site in the orbit26; the eyelid, retro-orbital space and lacrimal gland are other locations where the parasite may lodge27. Subretinal space is the most common location within the globe; the vitreous body and even optic nerve may be affected once it enters the choroidal circulation28. Orbital cysticercosis may present as a gradually increasing, painless, non-axial proptosis. Orbital rhabdomyosarcoma must be differentiated on the basis of imaging findings in a child who comes with this clinical picture. The patients may also present with poor vision, black spots or ocular discomfort, or may be entirely asymptomatic. Cysts lodged in the extraocular muscles may cause movement disorders or sudden central visual loss or a paracentral shadow and moving sensation when subretinal. Rarely the chorio-retinal lesion may cause iridocyclitis and retinal detachment12, 13. A-scan ultrasonography of subretinal cysticercosis reveals a high-amplitude echo corresponding to the inner cyst wall and overlying retina, which encloses a low-medium amplitude cystic cavity. B-scan ultrasonography reveals a convex curvilinear echo corresponding to the inner cyst wall and the overlying retina and surrounding a smaller round density representing the scolex. CECT will reveal a fluid attenuation lesion with an enhancing wall; an eccentric enhancing scolex may or may not be present. The cyst is hyperintense on T2 weighted images, isointense to normal vitreous and hypointense to the extraocular muscles on T1 weighted images, with an eccentric hypointense scolex on MRI (Figure 12). Surrounding tissues frequently show evidence of marked inflammation if the cyst is ruptured. Even in the absence of a scolex, imaging findings of a cystic lesion, or presence of myositis with positive serum ELISA for anti-cysticercus antibodies is confirmatory. Systemic albendazole with or without corticosteroids and are effective treatment. Surgery under cover of systemic Albendazole started two week prior is reserved for intraocular Cysticercosis. Parasitic cysts: Hydatid cyst Hydatid is the larval form of the parasite Echinococcus granulosus. Its natural hosts are carnivores like dogs that pass ova in their feces. These ova are ingested by herbivores and then larval forms develop in
their muscles. Human beings are accidental dead hosts infected by eating under cooked, infected meat of an animal. The larva can lodge anywhere in the body via the blood stream forming cysts. Orbital cysts are seen in 1% of the cases4, and patients present with slowly progressive proptosis. Sometimes, cyst rupture due to trauma may incite sever inflammatory reaction in the orbit. Imaging findings are non-specific - the cyst is seen as unilocular or multilocular hypodense mass which may cause bone remodeling if very large in size (Figure 13a). The “double wall sign” may be seen on ultrasound with the outer laminated ectocyst and the inner germinal layer forming the two layers of the cyst. On MRI, the cyst contents are of fluid signal intensity, hypointense on T1 and hyperintense on T2 weighted images. Orbital abscess Orbital inflammation due to microbial infection has been classified clinically into five groups by Chandler et al29: a) Preseptal cellulitis, b) Orbital cellulitis, c) Subperiosteal abscess, d) Orbital abscess, and e) Cavernous sinus thrombosis. The infections do not necessarily follow this sequential progression of events, as virulent infections and inappropriate treatment may cause complications early in the course of the disease. The most common source of infection are the ethmoid and frontal sinuses 30, odontogenic origin of infection is rare31. The infection spreads into the orbit from these primary sites via blood vessels or natural bony dehiscences32. Imaging (CT or MRI) plays a crucial role in imaging of infective conditions of the orbit, as it localizes and stages the disease, also detects complications early and can be used to monitor disease progression. Soft tissue stranding of the orbital fat is seen in orbital cellulitis on CT / MRI. A subperiosteal abscess is accumulation of pus between the periosteum and bony orbital wall. It seen as a flat / lentiform, rim enhancing collection on CT, which bows into the orbit and displaces the rectus muscle (Figure 14). Associated ethmoid or frontal sinusitis is frequently seen on imaging. An orbital abscess is seen as a similar cystic, peripherally enhancing lesion in the intraconal or extraconal space. Bone is usually not destroyed. Sonographic appearance of an abscess can be quite variable, ranging from collections that appear uniformly anechoic to those with irregularly hyperechoic internal echoes. Severe non axial or axial proptosis, ophthalmoplegia, visual decline and systemic toxicity are frequently associated clinical features. Sub-periosteal or intra-orbital abscess is an ophthalmic emergency. Intravenous antibiotics and drainage of collections form the cornerstone of management. Inflammatory pseudotumor and sino-nasal mucocele have to be considered in differential diagnosis.
Hematic cyst These cysts are formed from incompletely resorbed hematomas in the orbit, occurring in the soft tissues and as those occurring in bone. The etiology is multifactorial and includes trauma, foreign body retention, prior surgery, hematologic disorder (sickle cell disease, hemophilia), scurvy, uremia, venous hypertension, rickets and myelogeneous leukemia33. Hematomas may also secondarily form in a lymphangioma, dermoid, or hemangioma and is referred to as “chocolate cyst” in this setting34. Hematic cysts can also be classified as acute or chronic33- acute cysts are thin walled, post traumatic in etiology, and classically present with proptosis. Chronic hematic cysts have a thick wall composed of fibrous pseudocapsule, may cause bone erosion, and have complex internal contents composed of cholesterol crystals, hemosiderin, haemtoidin. They may gradually increase in size. Hematic cysts are most commonly situated sub-periosteally or within the diploe in the orbital roof 35. They are seen as well defined, sub-periosteal, non-enhancing masses that may erode adjacent bones. They are best seen on MRI as hyperintense on both T1 and T2 weighted images36 due to the presence of blood products that give rise to mixed signal intensity of the contents (Figure 15). Sonography may reveal large relatively anechoic mass. Hematic cysts are managed by surgical excision. Tumors Most of the orbital tumors are solid, but they may occasionally have a cystic component. Rhabdomyosarcoma3, optic nerve glioma4, basal cell carcinoma, schwannoma and adenoid cystic carcinoma are known to have cystic components. Imaging findings are non specific and diagnosis is based on pathology (Figures 16, 17). Aggressive tumors may show bone destruction and invasion of adjacent structures. CYSTS ARISING FROM ADJACENT STRUCTURES Mucocele Mucoceles are cystic lesion arise due to obstruction of ostia of the paranasal sinuses, resulting in accumulation of secretions within the sinus, causing gradual expansion of the sinus with thinning of its bony walls, and eventually eroding into neighboring orbit, nasopharynx or cranial cavity. Mucoceles are seen in fourth to seventh decades of life4 and commonly arise from frontal and ethmoid sinuses anteriorly. A congenital mucocele due to block of the nasolacrimal dust is seen in 2% of infants and children presenting with epiphora37. Cystic fibrosis is the most common predisposing factor in paranasal sinus mucoceles presenting pediatric age group, inflammation and trauma may be other contributing factors 38,39.
The frontal sinus mucocele, which is probably the most common mucocele, erodes the orbital roof and displaces the globe inferiorly, often causing diplopia and forms a palpable mass in the region of medial canthus. Mucoceles arising from sphenoid and posterior ethmoid sinuses may cause palsies of the optic and oculomotor nerves leading to visual symptoms and retro-orbital headache40. A mucocele of the maxillary sinus may lead to the unusual manifestation of “silent sinus syndrome4” in which erosion of the orbital floor by the mucocele causes enophthalmos. On CT a mucocele is seen as a non enhancing cystic mass expanding the paranasal sinuses with fluid attenuating contents. On MRI, the contents are hyperintense on T2-weighted images and hypointense on T1, but may be bright on T1-weighted images if the secretions become desiccated or purulent. With passage of time as the secretions become even more dehydrated, the lesion loses all signal and may not remain detectable on MRI. However, on CT the sinus contents will appear hyperdense. Cephalocele / Meningocele Cephaloceles result from congenital or acquired defects (Figure 18) in the bones of the calvarium37,41–43. A cephalocele is called a meningocele if contains meninges, encephalocele if it contains brain parenchyma, meningoencephalocele if it contains both brain parenchyma and meninges, and hydrencephalocele when it contains cerebral ventricle too. It may even contain a porencephalic cyst2,4. Frontoethmidal (sincipital) cephalo- / meningoceles are further classified as nasofrontal, nasoethmoidal and naso-orbital (anterior and posterior orbital)37. Anteriorly located cephaloceles occur due to defects in cribriform plate, frontal and lacrimal bones and present as pulsatile, fluctuant masses, located near the inner canthus or root of the nose, or project into the eyelids1. Posteriorly located cephaloceles result from defects in the optic foramen, sphenoid fissure, or orbital roof and medial wall, and present with unilateral proptosis1. Congenital midline cephaloceles are associated with orbital varices15, cranial defects and other facial anomalies2,37. MRI is the modality of choice MRI and it depicts the bony defect with an orbital soft tissue mass contiguous to brain parenchyma surrounded by CSF. A surgeon needs to be alerted preoperatively for the presence of a cephalocele as an orbital mass to prevent surgical catastrophe from occurring. Management consists of surgical excision, dural patching and closure of the bony defect.
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Figure captions: Figure 1. Intra-orbital dermoid in a 19-year-old boy with abaxial proptosis since childhood. Axial CT image shows a well circumscribed, encapsulated, extra-conal mass containing fat adjacent to a suture (arrow). Note the smooth remodelling of bony orbital wall. Axial T1W (a) T2W FS (b) MR images further confirms its fat signature.
Figure 2. Ruptured orbital dermoid in another patient. Axial CECT image shows an extraconal mass with a fat-fluid level (white arrow) - the lateral wall is ruptured and inflammation is extending into the temporal fossa. Figure 3. Conjunctival cyst in a 3-year old girl with swelling in left lower eyelid since last 5 months. Axial CT image shows a well defined, homogeneous, cystic lesion abutting the anterolateral aspect of left globe (arrow). The cyst was later excised with no clinical consequence. Figure 4. Colobomatous Cyst in a 4-year-old boy with a palpable mass in the right orbit. Coronal CT image shows a large colobomatous cyst on the superolateral aspect of the right orbit (arrow) and a microphthalmic globe (bold arrow). Figure 5. Colobomatous cyst in a 9-month-old male child with bilateral orbital masses since birth. Sagittal T2W MR image of the right orbit shows a fluid intensity cyst inferior to the globe. A presumed defect (arrow) in the coats of the microphthalmic globe is seen. The fellow eye is not shown. Figure 6. Congenital cystic eye in a 5-year-old boy with left orbital mass since birth. Axial (a) and sagittal (b) CT images show a large cyst occupying entire left orbit which shows expansion. Note the absence of recognizable left globe. Figure 7. Lymphangioma in a 12-year-old boy with recent onset right proptosis and early exposure keratitis. Axial T1W (a) and T2 W (b) MR images show an ill defined, transcompartmental, retrobulbar, multiloculated mass with hemorrhage and characteristic fluid-fluid levels (arrows). Multiple dense adhesions were found intra-operatively allowing only partial excision of lesion. Similar but milder episode that occurred two years back was treated conservatively. Figure 8. Lymphangioma in a 5-year-old child with proptosis that developed acutely in 12 hours. Coronal T1W (c) and T2W (d) MR images showing a large lobulated, intraconal mass, mildly hyperintense on T1 and brightly hyperintense on T2W MR images (arrows) suggestive of an acute bleed. The child was treated conservatively. Figure 9. Orbital varices in a 28-year-old man with intermittent proptosis. Axial (a) and coronal (b) CT images showing calcified phleboliths in varices (arrows). Axial (c) and coronal (d) T2W MR images in another patient show hyperintense, dilated tortuous venous channels in retrobulbar location which became clinically prominent during Valsalva maneuver. No active treatment was considered. Figure 10. Dacryocystocele in a 40-year-old man with epiphora and swelling near the inner canthus of right eye. Axial (a) and coronal (b) CT shows a low density, non enhancing cystic mass at the right
lacrimal fossa (arrow). There was obstruction at the junction of lacrimal sac and nasolacrimal duct. The patient became symptom free after Dacryocystorhinostomy. Figure 11. Optic nerve sheath meningocele in a 5-year-old girl with bilateral blurring of vision and congenital glaucoma. Axial (a) and sagittal (b) T2W MR images show expansion of bilateral optic nerve sheaths (arrows) with normal sized optic nerves. Note the deep cupping of optic discs. Figure 12. Intramuscular cysticercus in different patients (arrows). Small cyst with an eccentric scolex within the levator palpabrae superioris (a- sagittal T1WI), superior rectus (b- coronal T1WI). Figure 13. Hydatid cyst in a 20-year-old man presenting with painless proptosis of one year duration. A) Coronal CT image shows a unilocular, non enhancing, intraconal fluid density lesion in left orbit (arrow). B) The “double wall sign” seen in orbital hydatid cysts is seen in axial ultrasound image in another patient. Figure 14. Subperiosteal abscess in a 6-year-old boy. Axial (a) and coronal (b) CT images show left ethmoid and maxillary sinusitis and a lentiform subperiosteal abscess with rim enhancement along medial wall of left bony orbit, displacing the medial rectus muscle. Figure 15. Hematic cysts in a 2-year-old girl with scurvy presenting with bilateral abaxial proptosis. Coronal T2W MR image shows heterogeneous hyperintense masses in subperiosteal location along orbital roofs. Figure 16. Cystic schwannoma in 54-year-old lady with gradually progressive right proptosis. Axial (a) and coronal (b) CECT images show a well-defined intra- and extra-conal mass with thick walled cystic component and foci of peripheral calcification on superomedial aspect. The tumor was removed surgically and diagnosis confirmed on histopathology. Figure 17. Optic nerve glioma with a cystic change in an 8-year-old child with diminution of vision in the left eye. Axial post contrast T1 (a) and T2 (b) MR images show thickening of the posterior part of the intra-orbital course of optic nerve with hemorrhage and fluid-fluid level. The child had no stigmata of Neurobromatosis Type 1. Figure 18. Post-traumatic meningoencephalocele in a 4-year-old child. Axial CT image (a) depicts the fracture in right frontal bone. Sagittal T2-weighted MR image (b) shows the bony defect and the herniating brain parenchyma and meninges.
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Intra-orbital Cystic Lesions: An Imaging Spectrum Shivani Pahwa MD, Sanjay Sharma MD, FRCR, J. Das Chandan, Ekta Dhamija, Saurabh Agrawal MS
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Cite this article as: Shivani Pahwa MD, Sanjay Sharma MD, FRCR, J. Das Chandan, Ekta Dhamija, Saurabh Agrawal MS, Intra-orbital Cystic Lesions: An Imaging Spectrum, Curr Probl Diagn Radiol, http://dx.doi.org/10.1067/j.cpradiol.2015.03.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title: Intra-orbital Cystic Lesions: An Imaging Spectrum Category of paper: Review article Authors: 1. Dr Shivani Pahwa, MD Senior Resident, Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India - 110029 E mail: [email protected] Phone: 91-11-26593078 2. Dr Sanjay Sharma, MD, FRCR Professor, Department of Radiodiagnosis RP Centre of Ophthalmic Sciences All India Institute of Medical Sciences, New Delhi, India- 110029. E mail: [email protected] Phone : 91-11-26593053 3. Dr Chandan J Das Assistant Professor, Department of Radiodiagnosis All India Institute of Medical Sciences New Delhi, India- 110029. 4. Dr Ekta Dhamija Senior Resident, Department of Radiodiagnosis All India Institute of Medical Sciences
New Delhi, India – 110029 E mail: [email protected] 5. Dr Saurabh Agrawal, MS Research Officer, Department of Community Ophthalmology RP Centre of Ophthalmic Sciences All India Institute of Medical Sciences, New Delhi, India- 110029. Corresponding author: Dr Sanjay Sharma, MD, FRCR Department of Radiodiagnosis, AIIMS, New Delhi- 110029, India E mail: [email protected] Phone: 91-11-26593053 Grants received: None Source of funding: None Acknowledgements: None
Abstract Presence of a cyst or a cystic component in an intra-orbital mass often narrows the list of differential diagnoses to specific entities. Such a lesion in the orbit may arise from structures within the orbit, globe, and lacrimal system or from neighboring paranasal sinuses or meninges. Common congenital and developmental lesions encountered within the orbit include dermoids and epidermoids, and infrequently coloboma. Parasitic cysts (cysticercus), orbital abscess, mucocele, and vascular lesions are the most common acquired pathologies giving rise to fluid containing lesions within the orbit. The role of a
radiologist is crucial in expediting the diagnosis of orbital lesions with the help of characteristic imaging features on ultrasound, computed tomography (CT), or MR (magnetic resonance) Imaging. It also helps in identifying complications in others where formulation of an early and effective management strategy is vital for preserving vision. Introduction A cyst is a sac like structure lined by epithelium and containing fluid or semi-solid material. Cysts may be extraocular or rarely intraocular in location. The spectrum of such lesions is wide - it consists of rather easily managed benign lesions such as uncomplicated dermoids and parasitic cysts at one end to more sinister pathologies such as orbital abscesses and cystic malignant tumors on the other. These lesions are encountered across all age groups with varied clinical presentations. An orbital cyst may be an unsightly congenital cystic eye or colobomatous cyst in a neonate which portends a poor visual outcome, a venolymphatic malformation in a young child with an acute and often dramatic presentation, or an insidious, slowly enlarging mucocele presenting with proptosis in an adult 1. A superficial lesion often presents as a subcutaneous mass or nodule, whereas lesions located deep in the orbit may present with visual disturbances, proptosis, squint or signs and symptoms of inflammation2,3. Shields and Shields3 have classified orbital cystic lesions according to the cell of origin (Table 1). Kaufman et al2 proposed a simpler classification based on the etiology (Table 2). They classified cystic lesions of the orbit as congenital, acquired, and those arising from adjacent structures 1, 2 such as paranasal sinuses, brain and meninges. The organ of origin, cyst wall, internal contents and relationship to adjacent structures are well depicted both on CT and MRI. Bony abnormalities are well depicted on CT whereas MRI because of its excellent soft tissue contrast helps characterize the internal contents and wall characteristics of the lesions. However, because of widespread availability and short imaging time, CT often remains the workhorse of orbital imaging. A stepwise approach is useful in arriving at the correct diagnosis of orbital cystic lesions. Step 1: Look at the cyst contents: for presence of fat and calcification; dermoids are fat containing lesions. Step 2: Look at the exact location of the lesion within the orbit: Dermoids are usually located along lines of closure of sutures; orbital varices and colobomatous cysts are intraconal masses. In case of large masses, the epicenter of the lesion is usually the site of origin. Step3: Look at the relationship of the lesion to the globe, paranasal sinuses and floor of anterior cranial fossa. Colobomatous cysts lie adjacent to a microphthalmic eye; a mucocele will usually communicate
with the frontal or ethmoid sinus and meningocele will be associated with defect in the anterior skull base. In the following sections, we discuss the most commonly encountered lesions, their clinical presentation and radiologic features. CONGENITAL AND DEVELOPMENTAL ORBITAL CYSTS Choristoma (Dermoid, Epidermoid and Dermolipoma) A choristoma is defined as benign, disorganized proliferation of histologically normal tissues in an abnormal location4. Dermoid, epidermoid and dermolipoma are choristomas seen in orbit and are among the most common benign orbital tumors of childhood1,5. They arise from embryonic cell rests that get sequestered or implanted along lines of closure of sutures, meninges, or in the diploe, or due to failure of separation of these cell rests from mesoderm or endoderm1. Both dermoid and epidermoid are lined by squamous epithelium, but dermoids also contain cutaneous appendages as hair follicles, sweat and sebaceous glands. Dermoid cysts can also be classified as cutaneous and conjunctival dermoid cysts, which represent 59% of the total. Based on location, they can be classified as superficial or deep. Superficial dermoids are most commonly located along frontozygomatic (60%) and frontolacrimal (25%) sutures4, and present as painless, firm, subcutaneous periorbital masses in infancy or childhood. On imaging, they are seen as well defined, unilocular masses, with fluid or fat density contents, causing scalloping of the adjacent bone (Figure 1). About 15% may contain foci of calcification4. Presence of fat on imaging is pathognomonic. Deep dermoids and epidermoids present later in life as slow growing, discrete, well circumscribed, freely movable, intra-orbital or rarely intra-osseous masses causing proptosis and diplopia or with signs and symptoms of inflammation if they rupture or get infected. They are situated along suture lines, or even at the orbital apex, and may extend into the adjacent bones. Imaging is essential to establish the exact extent of these masses, because these may have dumbbell shaped extensions into the temporal fossa, intracranial cavity, or paranasal sinuses. If a choristoma is complicated by rupture or infection, CT / MRI will reveal an irregular wall, presence of inflammation in adjacent structures (Figure 1c), and irregularity of bony orbital walls. There may be a documented change in the longstanding image appearances. Dermolipomas are composed of mature fat cells with very little epithelial cells. They are located on the outer canthus of the eye beneath the conjunctiva or in the superotemporal epibulbar region and occasionally causes intermittent ocular irritation. These lesions are often non-cystic, and infiltrate into the peribulbar region, lid, and surrounding orbital tissues. When present, these lesions should not be surgically excised. Bilateral dermolipmas are seen in Goldenhaar’s syndrome1
The differential diagnosis for choristomas depends on the location: it may be of lacrimal gland origin for lesions located in the superotemporal quadrant; mucocele and encephalocele for superomedially located masses, and solid orbital tumors for inflamed masses in other locations. Superficial masses are managed by direct excision, whereas deep masses require combined orbital and neurosurgical approaches for removal. Occasionally, fistulization is seen after incomplete removal of orbital dermoid tumors. Hence defining the exact extent of the cystic mass and its relationship to adjacent structures on pre-operative imaging is crucial for management. Conjunctival cysts Conjunctival cysts are sequestrations of conjunctival and caruncular epithelia occurring in the superonasal aspect of the orbit without a bony defect. They are lined by non-keratinizing conjunctival epithelium and may be congenital or traumatic in origin. These are distinguished on the basis of a lack of historical or clinical evidence of trauma. They are most commonly located medially at or behind the caruncle, and may have fat or fluid contents (Figure 3). When large in size, they can cause motility disturbances, pain, or refractive errors6. In a case series of 11 patients, Goldstein et al6 found that larger conjunctival cysts caused mass effect leading to distortion of the globe in 6 patients, and bone remodeling in another 6. Hence imaging is essential when excision is being planned for a large conjunctival cyst; smaller lesions are managed by complete extirpation. Orbital germ cell tumors Orbital germ cell tumors are very rare tumors, with an unknown incidence. Teratomas are benign germ cell tumors that are seen as unilateral, rapidly growing orbital masses in infant girls 2. Primary orbital teratomas are confined to the orbit and are not associated with a bony defect, whereas combined teratomas extend into the periorbital tissues and cranial cavity. They are composed of cells derived from more than one germ layer, and present as large masses that cause diffuse expansion of the orbit and cause massive unilateral proptosis7,8. Vision is threatened by exposure keratopathy of the displaced globe, or due to stretching of the optic nerve. Defects of orbital bones are present in combined teratomas. Orbital yolk cell carcinomas and endodermal sinus tumors are malignant orbital tumors seen in children. On CT or MRI, germ cell tumors are seen as complex solid-cystic masses that cause expansion of the orbit (teratomas) that displace a normally formed globe, and may extend into periorbital structures or cranial cavity (combined teratomas, malignant germ cell tumors)7. Teratomas may have foci of fat and calcification. Teratomas are managed by surgical excision, with an attempt to preserve the globe, optic
nerve and eyelids8. Malignant orbital yolk cell carcinomas and endodermal sinus tumors are managed by chemotherapy and radiotherapy7. Colobomatous cysts and Morning glory anomaly A coloboma is a congenital or acquired fissure or gap in the coats of the eye, which may involve the sclera, choroid, retina, ciliary body, iris, lens or optic nerve head. Congenital colobomas are bilateral in upto 60%3, most commonly situated at the inferonasal quadrant. They result due to failure of closure of the embryonic fissure at the site of invagination of the optic vesicle. A colobomatous cyst is a neuroectoderm-lined mass that protrudes through a coloboma in the wall of a microphthalmic eye to form an orbital cyst which is connected to the globe with a tunnel like connection. The patient presents with a well formed but markedly small eye displaced by the colobomatous cyst, which may occupy the entire orbit (Figure 4). Colobomatous cysts may occur in isolation or in association with chromosomal anomalies and syndromes as Oculocerebrocutaneous syndrome (Dellman’s focal dermal hypoplasia (Goltz’s syndrome), brachiooculofacial syndrome, CHARGE (coloboma of the eye, heart defects, atresia of the choanae, retardation of growth and / or development, genitourinary and ear abnormalities) and VACTERL (vertebral defects, anal atresia, cardiac defects, trachea-esophageal fistula, renal anomalies, and limb abnormalities) syndromes3. On MRI, these cysts are hypointense on T1 weighted images, hyperintense on T2 weighted images, lie adjacent to the globe, are variable in size, but the exact site of communication between the cyst and the globe may not always be depicted on imaging (Figure 5). Excavation of the optic disc head in optic disc coloboma (Morning glory anomaly) is also well depicted on MRI. Congenital cystic eye, congenital microphthalmos and staphyloma must be considered in the differential diagnosis of a colobomatous cyst. Congenital cystic eye A congenital cystic eye is a rare anomaly that arises due to failure of the optic vesicle to differentiate into a globe9. The child presents at birth with a unilateral, unrecognizable eye. On CT or MRI, a large fluid containing, septated lesion is seen within an enlarged bony orbit2 (Figure 6). The contents have signal intensity of fluid (hypointense on T1 and hyperintense on T2 weighted images), as it is filled with serous fluid. A rudimentary optic nerve connected to the cyst may be seen. Documenting the absence of a microphthalmic eye and a well formed optic nerve on imaging is essential to distinguish congenital cystic eye from a colobomatous eye. Histopathology of an excised congenital cystic eye reveals fibrovascular connective tissue, primitive neuroglial elements, and dysplastic retinal cells. The cysts may enlarge with
time due to secretion of fluid by neuroglial cells. Congenital cystic eye is managed by surgical excision to preserve cosmesis. Craniofacial anomalies such as holoprosencepahly, hydrocephalus, cephaloceles, cleft lip and palate, and cardiac anomalies as Tetrology of Fallot have been described in patients with congenital cystic eye10,11. In a child who presents with an indiscernible globe or with a cystic mass in the eye at birth, the following three differentials should be considered: 1. Microphthalmos with colobomatous cyst, 2. Congenital cystic eye, and 3. Cystic germ cell tumor. ACQUIRED ORBITAL CYSTS Lymphangioma Venolymphatic malformations of the orbit are congenital vascular malformations that have a unique combination of clinical, radiologic and histologic features. They are vascular hamartomas that are isolated from systemic circulation4. They arise from venous anlage and are composed of diaphanous, serous filled, thin endothelium lined venous and lymphatic channels in a collagenous stroma. They also contain lymphoid cells which may proliferate with episodes of viral infection causing proptosis. They are classified into four types: superficial, deep, combined and complex4. Imaging is essential for their detection and defining the extent. Superficial lesions are externally visible and involve the conjunctiva or the eyelid only. They can be easily removed if disfiguring. Deep lesions classically present as sudden proptosis and diplopia in a young boys due to hemorrhage, which may be spontaneous or triggered by trivial trauma. Recurrent hemorrhage leads to formation of a blood filled chocolate cyst. Combined lesions have both superficial and deep components. Complex lesions have extensive vascular malformations with facial, intracranial and systemic abnormalities apart from the orbital component12,13. Sonography reveals a poorly outlined, irregular orbital lesion with low internal reflectivity but highly echogenic internal septae. Contrast enhanced CT will demonstrate an ill-defined, unencapsulated, multilocular, infiltrating, cyst like mass, involving extraconal and intraconal spaces, often showing rim like enhancement. It may have hyperdense contents due to presence of hemorrhage. On MRI, the contents show mixed signal intensity contents on T1 and T2 weighted images due to presence of blood degradation products of varying ages (Figures 7, 8). The presence of fluid-fluid levels due to repeated hemorrhage is characteristic14. Almost half of these patients go on to develop compressive optic neuropathy due to recurrent hemorrhages. Management consists of surgical decompression and evacuation of hematic cysts if acute hemorrhage is causing optic neuropathy. However, total excision is usually not possible due to formation of dense
adhesions with surrounding normal orbital tissues. Hemangiomas and pseudotumors should be considered in the differential diagnosis of these lesions. Both hemangiomas and pseudotumors are well defined, solid masses on imaging and show intense contrast enhancement. Orbital varix These are low flow, distensible, congenital venous malformation composed of abnormally large veins with systemic connection, causing intermittent reversible proptosis13.They are the most common cause of spontaneous orbital hemorrhage. Islam et al15 have described that orbital varices are associated with craniofacial anomalies in 4.5% of the patients. These include major midline encepahaloceles, superomedial defects of the orbital wall, and defects of the greater wing of sphenoid. On ultrasound the finding of an anechoic retrobulbar lesion that exhibits intrinsic flow during the Valsalva maneuver is indicative of a varix, and color Doppler imaging may demonstrate a reversal of flow toward the transducer during the Valsalva maneuver. Dynamic contrast enhanced CT done in prone position or while performing Valsalva maneuver is the technique of choice; the lesion may not be apparent on supine scanning. Imaging shows a tortuous, intensely enhancing lesion that increases in size on Valsalva; phleboliths may also be seen (Figure 9). MRI shows a complex signals with blood products. Thrombosis or hemorrhage may occur in a varix following trauma, forming a chocolate cyst. The differential diagnosis would be lymphangioma and cavernous hemangioma. Smaller lesions are managed conservatively by watchful expectancy and periodic follow up. Surgical intervention via orbitotomy is indicated when large varices raise orbital pressure causing functional deficit or intractable pain, and cosmetic disfigurement16. Dacryocele A dacryocele is seen as a painless, slow growing mass formed due to blockage of excretory ducts of lacrimal glands. It is situated at the outer canthus of the eye if due to blockage of the main lacrimal gland, at the medial canthus if due to blockage of the nasolacrimal duct, and in the conjunctival fornices if ducts of accessory glands of Wolfring and Krause are blocked17. The blockage may be congenital (in neonates)18, post traumatic or infective in origin, or it may be caused due to blockage by a slowly growing lacrimal tumor19. Rarely, the epithelium of the cyst may itself transform into a squamous cell carcinoma 20. Clinically, the dacryocele is firm, non tender and is not compressible, the presence of a bluish discoloration and confirmation with imaging studies as ultrasonography, or nasal endoscopy aid in diagnosis. Congenital dacryoceles are commonly associated with intranasal mucoceles, dacryocystitis, and preseptal cellulitis18.
A dacryocele has non-specific imaging appearance and is seen as a well defined, cystic, non-enhancing lesions centered at lacrimal fossa (Figure 10). It is hypointense on T1 and hyperintense on T2 weighted images. Orbital dermoid and epidermoid, lacrimal gland tumors and frontal mucoceles are the important differential diagnosis for masses in this location. Management is firm pressure or probing or endoscopic excision. Epithelial appendage cysts Tiny (<1 cm), cystic lesions may be seen in the eyelids or superficial orbit due to blockage of ducts of the skin appendages (sebaceous glands, sweat glands) or conjunctiva. Chalazion is the most common epithelial appendage cyst in the lids and is caused by the blockage of Meibomian glands. These lesions are best diagnosed clinically. Imaging is not necessary. Optic nerve sheath meningocele Dural ectasia of optic nerve or optic nerve sheath meningocele21 refers to tubular-cystic enlargement of the dural sheath around the optic nerve. It is a rare condition typically seen in middle age. Hayreh et al 22 noted that the perioptic subarachanoid space is narrowest at the cranio-orbital junction, and hence bony malformations of this region could lead to excessive CSF collection in the optic nerve sheath. However, cystic enlargement of optic nerve sheath occurs most commonly secondary to glaucoma or neoplastic apical masses as a meningioma, optic nerve pilocytic astrocytoma, hemangioma, or due to fractures of cranio-orbital junction23,24. Association with neurofibromatosis type 1, von Hippel-Lindau disease, acquired hypermetropia and choroidal folds is also well known. It may also be associated with empty sella and enlarged subarachnoid cisterns2. Its relationship with raised intracranial tension has not been proven and remains a matter of speculation. Garrity et al
21
introduced the term ‘optic nerve sheath meningocele’ in 1990 to describe cases in which
ectasia of the optic nerve sheath was seen in the absence of an orbital apex mass or congenital malformation of the orbital apex. Patients present with slow or rapid onset of visual disturbances and reduced field of vision and headache. CT or MRI reveal a fusiform or saccular dilatation of the duraarachanoid sheath with a relatively normal appearing optic nerve (Figure 11). Optic nerve tumors such as gliomas, meningiomas, and arachnoid cysts involving the optic nerve sheath must be considered as differential diagnosis. Surgical decompression of the optic nerve sheath should be contemplated for patients presenting with rapid visual loss over 3-6 months23,24.
Parasitic cysts: cysticercus cellulosae Cysticercus cellulosae is the larval form of the pork tapeworm, taenia solium, and is the most common intra-orbital parasitic infection seen in endemic areas25. Humans are intermediate hosts and acquire the infection by feco-oral route by ingestion of eggs through contaminated food and water. The disease is more common in children and young adults. The ova develop into larvae in the intestine, reach the portal circulation, and hence forth get disseminated into the body through the systemic circulation. The cysts are most commonly seen in the subcutaneous tissues, muscles, brain and eyes. Extraocular muscles are the most commonly affected site in the orbit26; the eyelid, retro-orbital space and lacrimal gland are other locations where the parasite may lodge27. Subretinal space is the most common location within the globe; the vitreous body and even optic nerve may be affected once it enters the choroidal circulation28. Orbital cysticercosis may present as a gradually increasing, painless, non-axial proptosis. Orbital rhabdomyosarcoma must be differentiated on the basis of imaging findings in a child who comes with this clinical picture. The patients may also present with poor vision, black spots or ocular discomfort, or may be entirely asymptomatic. Cysts lodged in the extraocular muscles may cause movement disorders or sudden central visual loss or a paracentral shadow and moving sensation when subretinal. Rarely the chorio-retinal lesion may cause iridocyclitis and retinal detachment12, 13. A-scan ultrasonography of subretinal cysticercosis reveals a high-amplitude echo corresponding to the inner cyst wall and overlying retina, which encloses a low-medium amplitude cystic cavity. B-scan ultrasonography reveals a convex curvilinear echo corresponding to the inner cyst wall and the overlying retina and surrounding a smaller round density representing the scolex. CECT will reveal a fluid attenuation lesion with an enhancing wall; an eccentric enhancing scolex may or may not be present. The cyst is hyperintense on T2 weighted images, isointense to normal vitreous and hypointense to the extraocular muscles on T1 weighted images, with an eccentric hypointense scolex on MRI (Figure 12). Surrounding tissues frequently show evidence of marked inflammation if the cyst is ruptured. Even in the absence of a scolex, imaging findings of a cystic lesion, or presence of myositis with positive serum ELISA for anti-cysticercus antibodies is confirmatory. Systemic albendazole with or without corticosteroids and are effective treatment. Surgery under cover of systemic Albendazole started two week prior is reserved for intraocular Cysticercosis. Parasitic cysts: Hydatid cyst Hydatid is the larval form of the parasite Echinococcus granulosus. Its natural hosts are carnivores like dogs that pass ova in their feces. These ova are ingested by herbivores and then larval forms develop in
their muscles. Human beings are accidental dead hosts infected by eating under cooked, infected meat of an animal. The larva can lodge anywhere in the body via the blood stream forming cysts. Orbital cysts are seen in 1% of the cases4, and patients present with slowly progressive proptosis. Sometimes, cyst rupture due to trauma may incite sever inflammatory reaction in the orbit. Imaging findings are non-specific - the cyst is seen as unilocular or multilocular hypodense mass which may cause bone remodeling if very large in size (Figure 13a). The “double wall sign” may be seen on ultrasound with the outer laminated ectocyst and the inner germinal layer forming the two layers of the cyst. On MRI, the cyst contents are of fluid signal intensity, hypointense on T1 and hyperintense on T2 weighted images. Orbital abscess Orbital inflammation due to microbial infection has been classified clinically into five groups by Chandler et al29: a) Preseptal cellulitis, b) Orbital cellulitis, c) Subperiosteal abscess, d) Orbital abscess, and e) Cavernous sinus thrombosis. The infections do not necessarily follow this sequential progression of events, as virulent infections and inappropriate treatment may cause complications early in the course of the disease. The most common source of infection are the ethmoid and frontal sinuses 30, odontogenic origin of infection is rare31. The infection spreads into the orbit from these primary sites via blood vessels or natural bony dehiscences32. Imaging (CT or MRI) plays a crucial role in imaging of infective conditions of the orbit, as it localizes and stages the disease, also detects complications early and can be used to monitor disease progression. Soft tissue stranding of the orbital fat is seen in orbital cellulitis on CT / MRI. A subperiosteal abscess is accumulation of pus between the periosteum and bony orbital wall. It seen as a flat / lentiform, rim enhancing collection on CT, which bows into the orbit and displaces the rectus muscle (Figure 14). Associated ethmoid or frontal sinusitis is frequently seen on imaging. An orbital abscess is seen as a similar cystic, peripherally enhancing lesion in the intraconal or extraconal space. Bone is usually not destroyed. Sonographic appearance of an abscess can be quite variable, ranging from collections that appear uniformly anechoic to those with irregularly hyperechoic internal echoes. Severe non axial or axial proptosis, ophthalmoplegia, visual decline and systemic toxicity are frequently associated clinical features. Sub-periosteal or intra-orbital abscess is an ophthalmic emergency. Intravenous antibiotics and drainage of collections form the cornerstone of management. Inflammatory pseudotumor and sino-nasal mucocele have to be considered in differential diagnosis.
Hematic cyst These cysts are formed from incompletely resorbed hematomas in the orbit, occurring in the soft tissues and as those occurring in bone. The etiology is multifactorial and includes trauma, foreign body retention, prior surgery, hematologic disorder (sickle cell disease, hemophilia), scurvy, uremia, venous hypertension, rickets and myelogeneous leukemia33. Hematomas may also secondarily form in a lymphangioma, dermoid, or hemangioma and is referred to as “chocolate cyst” in this setting34. Hematic cysts can also be classified as acute or chronic33- acute cysts are thin walled, post traumatic in etiology, and classically present with proptosis. Chronic hematic cysts have a thick wall composed of fibrous pseudocapsule, may cause bone erosion, and have complex internal contents composed of cholesterol crystals, hemosiderin, haemtoidin. They may gradually increase in size. Hematic cysts are most commonly situated sub-periosteally or within the diploe in the orbital roof 35. They are seen as well defined, sub-periosteal, non-enhancing masses that may erode adjacent bones. They are best seen on MRI as hyperintense on both T1 and T2 weighted images36 due to the presence of blood products that give rise to mixed signal intensity of the contents (Figure 15). Sonography may reveal large relatively anechoic mass. Hematic cysts are managed by surgical excision. Tumors Most of the orbital tumors are solid, but they may occasionally have a cystic component. Rhabdomyosarcoma3, optic nerve glioma4, basal cell carcinoma, schwannoma and adenoid cystic carcinoma are known to have cystic components. Imaging findings are non specific and diagnosis is based on pathology (Figures 16, 17). Aggressive tumors may show bone destruction and invasion of adjacent structures. CYSTS ARISING FROM ADJACENT STRUCTURES Mucocele Mucoceles are cystic lesion arise due to obstruction of ostia of the paranasal sinuses, resulting in accumulation of secretions within the sinus, causing gradual expansion of the sinus with thinning of its bony walls, and eventually eroding into neighboring orbit, nasopharynx or cranial cavity. Mucoceles are seen in fourth to seventh decades of life4 and commonly arise from frontal and ethmoid sinuses anteriorly. A congenital mucocele due to block of the nasolacrimal dust is seen in 2% of infants and children presenting with epiphora37. Cystic fibrosis is the most common predisposing factor in paranasal sinus mucoceles presenting pediatric age group, inflammation and trauma may be other contributing factors 38,39.
The frontal sinus mucocele, which is probably the most common mucocele, erodes the orbital roof and displaces the globe inferiorly, often causing diplopia and forms a palpable mass in the region of medial canthus. Mucoceles arising from sphenoid and posterior ethmoid sinuses may cause palsies of the optic and oculomotor nerves leading to visual symptoms and retro-orbital headache40. A mucocele of the maxillary sinus may lead to the unusual manifestation of “silent sinus syndrome4” in which erosion of the orbital floor by the mucocele causes enophthalmos. On CT a mucocele is seen as a non enhancing cystic mass expanding the paranasal sinuses with fluid attenuating contents. On MRI, the contents are hyperintense on T2-weighted images and hypointense on T1, but may be bright on T1-weighted images if the secretions become desiccated or purulent. With passage of time as the secretions become even more dehydrated, the lesion loses all signal and may not remain detectable on MRI. However, on CT the sinus contents will appear hyperdense. Cephalocele / Meningocele Cephaloceles result from congenital or acquired defects (Figure 18) in the bones of the calvarium37,41–43. A cephalocele is called a meningocele if contains meninges, encephalocele if it contains brain parenchyma, meningoencephalocele if it contains both brain parenchyma and meninges, and hydrencephalocele when it contains cerebral ventricle too. It may even contain a porencephalic cyst2,4. Frontoethmidal (sincipital) cephalo- / meningoceles are further classified as nasofrontal, nasoethmoidal and naso-orbital (anterior and posterior orbital)37. Anteriorly located cephaloceles occur due to defects in cribriform plate, frontal and lacrimal bones and present as pulsatile, fluctuant masses, located near the inner canthus or root of the nose, or project into the eyelids1. Posteriorly located cephaloceles result from defects in the optic foramen, sphenoid fissure, or orbital roof and medial wall, and present with unilateral proptosis1. Congenital midline cephaloceles are associated with orbital varices15, cranial defects and other facial anomalies2,37. MRI is the modality of choice MRI and it depicts the bony defect with an orbital soft tissue mass contiguous to brain parenchyma surrounded by CSF. A surgeon needs to be alerted preoperatively for the presence of a cephalocele as an orbital mass to prevent surgical catastrophe from occurring. Management consists of surgical excision, dural patching and closure of the bony defect.
Conclusion Cystic lesions in the orbit are frequently encountered in clinical practice. The knowledge of specific imaging features enables accurate diagnosis, facilitates appropriate management and helps avoid complications. References: 1.
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Figure captions: Figure 1. Intra-orbital dermoid in a 19-year-old boy with abaxial proptosis since childhood. Axial CT image shows a well circumscribed, encapsulated, extra-conal mass containing fat adjacent to a suture (arrow). Note the smooth remodelling of bony orbital wall. Axial T1W (a) T2W FS (b) MR images further confirms its fat signature.
Figure 2. Ruptured orbital dermoid in another patient. Axial CECT image shows an extraconal mass with a fat-fluid level (white arrow) - the lateral wall is ruptured and inflammation is extending into the temporal fossa. Figure 3. Conjunctival cyst in a 3-year old girl with swelling in left lower eyelid since last 5 months. Axial CT image shows a well defined, homogeneous, cystic lesion abutting the anterolateral aspect of left globe (arrow). The cyst was later excised with no clinical consequence. Figure 4. Colobomatous Cyst in a 4-year-old boy with a palpable mass in the right orbit. Coronal CT image shows a large colobomatous cyst on the superolateral aspect of the right orbit (arrow) and a microphthalmic globe (bold arrow). Figure 5. Colobomatous cyst in a 9-month-old male child with bilateral orbital masses since birth. Sagittal T2W MR image of the right orbit shows a fluid intensity cyst inferior to the globe. A presumed defect (arrow) in the coats of the microphthalmic globe is seen. The fellow eye is not shown. Figure 6. Congenital cystic eye in a 5-year-old boy with left orbital mass since birth. Axial (a) and sagittal (b) CT images show a large cyst occupying entire left orbit which shows expansion. Note the absence of recognizable left globe. Figure 7. Lymphangioma in a 12-year-old boy with recent onset right proptosis and early exposure keratitis. Axial T1W (a) and T2 W (b) MR images show an ill defined, transcompartmental, retrobulbar, multiloculated mass with hemorrhage and characteristic fluid-fluid levels (arrows). Multiple dense adhesions were found intra-operatively allowing only partial excision of lesion. Similar but milder episode that occurred two years back was treated conservatively. Figure 8. Lymphangioma in a 5-year-old child with proptosis that developed acutely in 12 hours. Coronal T1W (c) and T2W (d) MR images showing a large lobulated, intraconal mass, mildly hyperintense on T1 and brightly hyperintense on T2W MR images (arrows) suggestive of an acute bleed. The child was treated conservatively. Figure 9. Orbital varices in a 28-year-old man with intermittent proptosis. Axial (a) and coronal (b) CT images showing calcified phleboliths in varices (arrows). Axial (c) and coronal (d) T2W MR images in another patient show hyperintense, dilated tortuous venous channels in retrobulbar location which became clinically prominent during Valsalva maneuver. No active treatment was considered. Figure 10. Dacryocystocele in a 40-year-old man with epiphora and swelling near the inner canthus of right eye. Axial (a) and coronal (b) CT shows a low density, non enhancing cystic mass at the right
lacrimal fossa (arrow). There was obstruction at the junction of lacrimal sac and nasolacrimal duct. The patient became symptom free after Dacryocystorhinostomy. Figure 11. Optic nerve sheath meningocele in a 5-year-old girl with bilateral blurring of vision and congenital glaucoma. Axial (a) and sagittal (b) T2W MR images show expansion of bilateral optic nerve sheaths (arrows) with normal sized optic nerves. Note the deep cupping of optic discs. Figure 12. Intramuscular cysticercus in different patients (arrows). Small cyst with an eccentric scolex within the levator palpabrae superioris (a- sagittal T1WI), superior rectus (b- coronal T1WI). Figure 13. Hydatid cyst in a 20-year-old man presenting with painless proptosis of one year duration. A) Coronal CT image shows a unilocular, non enhancing, intraconal fluid density lesion in left orbit (arrow). B) The “double wall sign” seen in orbital hydatid cysts is seen in axial ultrasound image in another patient. Figure 14. Subperiosteal abscess in a 6-year-old boy. Axial (a) and coronal (b) CT images show left ethmoid and maxillary sinusitis and a lentiform subperiosteal abscess with rim enhancement along medial wall of left bony orbit, displacing the medial rectus muscle. Figure 15. Hematic cysts in a 2-year-old girl with scurvy presenting with bilateral abaxial proptosis. Coronal T2W MR image shows heterogeneous hyperintense masses in subperiosteal location along orbital roofs. Figure 16. Cystic schwannoma in 54-year-old lady with gradually progressive right proptosis. Axial (a) and coronal (b) CECT images show a well-defined intra- and extra-conal mass with thick walled cystic component and foci of peripheral calcification on superomedial aspect. The tumor was removed surgically and diagnosis confirmed on histopathology. Figure 17. Optic nerve glioma with a cystic change in an 8-year-old child with diminution of vision in the left eye. Axial post contrast T1 (a) and T2 (b) MR images show thickening of the posterior part of the intra-orbital course of optic nerve with hemorrhage and fluid-fluid level. The child had no stigmata of Neurobromatosis Type 1. Figure 18. Post-traumatic meningoencephalocele in a 4-year-old child. Axial CT image (a) depicts the fracture in right frontal bone. Sagittal T2-weighted MR image (b) shows the bony defect and the herniating brain parenchyma and meninges.
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