Orbital masses

Orbital Masses Kelly K. Koeller and James G. Smirniotopoulos The "space approach" will be introduced as a means of analyzing orbital masses on imaging studies. Determination in which space an orbital mass resides, the character of its margin, the presence or absence of bony changes, and evidence of extension of the mass beyond the orbit often allows the radiologist to narrow the differential diagnosis and provides essential information to the ophthalmologist for definitive diagnosis and treatment planning. This is a U S g o v e r n m e n t work. There are no restrictions on its use.

S DISCUSSED in greater detail elsewhere in this series, the retrobulbar orbit can be divided into three areas or "spaces." The "cone" or "conal space" is composed of the four rectus muscles and the thin intermuscular membrane which joins them and extends posteriorly to the insertion of the muscle tendons on the annulus of Zinn at the orbital apex. The "intraconal space" is the region of the orbit which lies within the "cone." The "extraconal space" is the region of the orbit which lies outside of the "cone." These three spaces are more than just interesting anatomic details because they provide a method of analysis of an orbital mass encountered on an imaging study. By defining from which space an orbital mass arises, in combination with other imaging features, the radiologist can carefully narrow the differential diagnosis to only a few possibilities. In general, benign orbital masses can be distinguished from malignant ones by certain clinicoradiological features. Benign lesions are usually slow-growing, well-marginated, and may remodel bone but not destroy it. On the other hand, malignant lesions are usually rapidly growing, poorly marginated, show bone destruction, and commonly extend through the orbital fissures. Enhancement of an orbital lesion usually indicates increased vascularity. I This article will address the wide spectrum of

A

From the Department of Radiologic Pathology, Armed Forces Institute of Pathology, Washington, DC and the Department of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD. The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or representing the views of the United States Navy or the Department of Defense. Address reprint requests to Kelly K. Koeller, CDR, MC, USN, Department of Radiologic Pathology, Armed Forces Institute of Pathology, Rm M-121, 14th St at Alaska Ave, Washington, DC 20306-6000. This is a US government work. There are no restrictions on its use,

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lesions that may present as orbital masses by emphasizing the "space approach" to these lesions along with radiologic-pathologic correlation with computed tomography (CT) and magnetic resonance (MR) imaging. The lesions will be grouped according to a common pathology. Tables 1, 2, 4, and 5 classify the lesions according to their predominant location within the intraconal space, extraconal space, lacrimal gland region, and lacrimal sac region. Table 3 lists those lesions which have a propensity for intercompartmental involvement. NERVE SHEATH TUMORS Schwannoma

Clinical Schwannomas account for 1% to 6% of all orbital masses. 1,2 They are found more commonly in adults. Because the vast majority of these neoplasms are benign, they typically have insidious clinical presentations. They present as slowly growing masses with slowly progressive painless proptosis frequently associated with diplopia, strabismus, papilledema and, if optic nerve compression occurs, optic atrophy. 1 They may occur as in isolation or in association with neurofibromatosis. Of all neurofibromatosis patients, up to one in five will develop a schwannoma.

Pathology Schwannomas arise from branches of orbital cranial nerves (III, IV, V, and VI), sympathetic and parasympathetic fibers, and the ciliary ganglion. Most arise from Va. 1 Consequently, and reflecting the benign histology, these tumors usually present as intraconal, ovoid-to-fusiform masses3 They are well-circumscribed and usually homogeneous on gross pathological examination because a thin, fibrous capsule derived from compressed perineural tissue surrounds the tumor. Occasionally, particularly in larger lesions and in atypical variants,

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ORBITAL MASSES Table 1. Intraconal Lesions

Table 3. Intercompartmental Lesions

Common Cavernous hemangioma Schwannoma (1% to 6% of all orbital masses) Neurofibroma (localized type) (2.4% for all types) Lymphoma (no. 3 cause of proptosis) Fibrous histiocytoma (1% of all orbital masses) Uncommon Capillary hemangioma (children) Rhabdomyosarcoma (nonembryonal types, children) Malignant rhabdoid tumor (children) Primary orbital melanoma Leiomyoma Leiomyosarcoma Granular cell tumor Hemangiopericytoma Venous varix Arteriovenous malformation

Lymphangiema Rhabdomyosarcoma Neurofibroma (plexiform and diffuse) Capillary hemangioma Venous varix Arteriovenous malformation

cystic degeneration and intralesional hemorrhage occurs, producing a heterogeneous appearance.1 Microscopically, schwannomas are composed of two types of Schwann cells: Antoni A, which are characterized by a dense population of spindleshaped cells, and the less dense Antoni B cells, which have a more "foamy" appearance. Atypia and mitotic figures are absent in the benign schwannomas.1 Table 2. Extraconal Lesions

Common Lymphoma Lymphangioma Metastasis Adults: breast, lung, unknown primary, prostate, melanoma Children: neuroblastoma, Ewing sarcoma, leukemia Rhabdomyosarcoma (embryonal type, children) Dermoid Epidermal inclusion cyst Paranasal sinus neoplasms Uncommon Cavernous hemangioma Capillary hemangioma (children) Langerhans cell histiocytosis (<1% of all orbital masses) Fibromatosis (most common orbital lesion of infancy) Teratoma Hematic cyst Hemangiopericytoma Burkitt's lymphoma Granulocytic sarcoma Primary osseous neoplasm Ossifying fibroma Osteoma Plasmacytoma/multiple myeloma (0.5% of all orbital masses) Osteosarcoma

Imaging CT. Schwannomas present as well-marginated ovoid-to fusiform masses (Fig 1). 3 A mildly heterogeneous appearance is typical, reflecting the Antoni A and Antoni B cell populations. Antoni A fibers are believed to produce higher density (similar to the density of muscle), whereas the abundant cytoplasm of the Antoni B fibers likely accounts for low density areas. Cystic changes, and hemosiderinladen macrophages may also account for hypodensity within these lesions. Schwannomas may either displace or engulf the optic nerve.1 MR. These masses have low-to intermediate signal intensity on Tl-weighted images (TlWI) and hyperintensity on T2-weighted images (T2WI). Usually there is marked internal enhancement of the tumor.1 Neurofibroma

Clinical Like schwannomas, neurofibromas are tumors of nerve sheath origin. In the orbit, neurofibromas are less common than schwannomas, accounting for about 2.4% of all orbital masses. 4 Although most are seen in von Recklinghausen's disease, they may occur as an isolated finding. There are three subtypes: localized, plexiform, and diffuse. The localized form of neurofibroma has a virtually identical clinical presentation as Table 4. Lacrimal Gland Lesions

Epithelial neoplasms (50%) Benign (50%) Benign mixed tumor (pleomorphic adenoma) Malignant (50%) Epithelial carcinoma Adenoid cystic carcinoma Malignant mixed tumor Metastasis Lymphoproliferative/Inflam matory (50%) Lymphoma Pseudotumor SjSgren's Sarcoid Granulocytic sarcoma (chloroma)

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KOELLER AND SMIRNIOTOPOULOS Table 5. Lacrimal Sac Lesions

Malignant (90%) Carcinoma Squamous Transitional Adenoid cystic Oncocytic adenocarcinoma Mucoepidermoid Melanoma Hemangiopericytoma Lymphoma Metastasis Benign (10%) Mucocele Polyp Fibroma Fibrous histiocytoma Oncocytoma Oxyphillic adenoma

schwannomas; typically, there is gradual onset of unilateral exophthalmos and strabismus over months to years in a patient between 20 and 50 years of age. They occur most often in the upper part of the orbit or lacrimal fossa. Approximately 10% are associated with neurofibromatosis. 5 Plexiform neurofibromas, on the other hand, occur much earlier in life and present frequently with a pulsatile exophthalmos because of the transmission of cerebrospinal fluid pulsations

through a defect in the sphenoid wing secondary to sphenoid wing dysplasia. Plexiform neurofibromas are a pathognomonic manifestation of neurofibromatosis. Diffuse neurofibromas have a variable association with neurofibromatosis. They present in the first two decades of life, usually between 2 and 5 years of age. On clinical examination, these lesions characteristically present as a "bag of worms," a palpable vermiform mass, secondary to highly vascular nature of these lesions.

Pathology Neurofibromas usually present as a mass in the superior half of the orbit or retrobulbar space. 5 Like schwannomas, they are composed of Schwann cells but unlike schwannomas, they also contain endoneural fibroblasts, perineural cells, and peripheral nerve axons. Although they do not have a capsule to enclose the tumor, localized neurofibromas still present as a well-circumscribed mass on gross pathological examination. This subtype is much less vascular than either the plexiform or diffuse subtypes. Both plexiform and diffuse neurofibromas are infiltrative and highly vascular lesions, which are distinguished histologically by the presence of a perineural sheath around each neuroma-

Fig 1. Schwannoma. (A) Contrast-enhanced CT scan shows well-defined enhancing intraconal soft tissue mass producing proptosis of the left globe, The medial rectus muscle is displaced and stretched against the medial orbital wall, Mild scalloping of the lateral orbital wall is seen. (B) Sagittal T I W image without contrast shows homogeneous mass with signal intensity of extraocular muscles (arrows), It abuts the posterior margin of the globe without producing indentation of the globe itself, (C) Cut specimen photograph shows predominantly homogeneous pattern of this encapsulated neoplasm,

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tous unit in the plexiform subtype. Because of the infiltrative nature of these two subtypes, they are extremely difficult to completely resect.

Imaging CT. Localized neurofibromas are isodense to muscle on noncontrast CT studies. They may contain foci of calcification and may remodel or expand the bony orbit. They enhance uniformly. 1 Plexiform and diffuse neurofibromas present as ill-defined, moderately enhancing masses, frequently associated with sphenoid wing dysplasia. After surgical enucleation, amputation neuromas may occur; these are usually hyperdense, although occasional cystic appearances have been described. 1 MR. Localized neurofibromas have signal intensity similar to that of the extraocular muscles on T1WI and are hyperintense on T2WI. Diffuse neurofibromas may have hyperintensity on T1WI, probably secondary to deposition of xanthomatous cells. Plexiform neurofibromas are more heterogeneous in appearance secondary to variably sized nerve thickenings and tumor subunits. They are hypointense on T1WI and may extend to the infratemporal fossa through the orbital fissures of the posterior orbit.

LYMPHOID DISORDERS Lymphoproliferative disorders account for 10% of all orbital disease, involving the conjunctiva, orbit, lacrimal gland, and eyelid. 6 Approximately one-third of cases are associated with systemic disease, with almost all of these cases occurring sometime in the course of the disease rather than as the initial presentation. Of all the sites within the orbit, those occurring in the eyelid have the greatest likelihood of being associated with systemic lymphoma. 6 The presence of bilateral orbital lesions does not predispose to systemic disease. 7 Pseudolymphomas are associated with systemic lymphoma in 25% of cases. 6 Approximately l% of systemic lymphoma patients have some form of orbital lymphoma during the course of the disease. 8

Lymphoma

Clinical After inflammation and hemangioma, lymphoma is the third most common cause of proptosis. The

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average age of presentation is 50 years old, and females are more commonly afflicted than males. 9 Usually of insidious onset, lymphoma typically presents with proptosis, ptosis, diplopia, motility disorders, and vision problems over several weeks to months. 6 Direct involvement of the extraocular muscles (EOMs) is rare, but limitation of EOM motion more commonly occurs as a result of direct compression. 6 Those involving the eyelid may present more rapidly than other sites, sometimes in as little as 2 weeks, especially if poorly differentiated. 8 When they involve the lacrimal gland, distinction from pleomorphic adenoma is important because direct biopsy of suspected lacrimal lymphoma is recommended to avoid the risk of iatrogenic spread of the disease during an attempt for total excision, m whereas biopsy of a suspected pleomorphic adenoma is contraindicated to avoid an increased recurrence rate secondary to iatrogenic spilling of the tumor contents. 6 Once diagnosed, lymphoma, a radiosensitive tumor, is treated by external beam radiation therapy (20 to 30 Gy) with shielding of the globe. 6

Pathology Most orbital lymphomas are of the B-cell type (non-Hodgkin's lymphoma) in adults. 8 In children, nodular lymphoma usually occurs in the lacrimal gland, whereas the diffuse type tends to involve the intraconal space, n Of all orbital sites, the lacrimal gland is the most common orbital structure involved. Bone destruction is rarely seen in orbital lymphoma, which may aid in distinguishing this hypovascular disease from other hypovascular softtissue neoplasms. 6,8 On microscopy, lymphoma is characterized by two forms: diffuse sheeting of neoplastic cells (more common), or discrete nodular foci suggesting germinal centers (less common). 8

Imaging CT. CT is the preferred imaging modality in the evaluation of orbital lymphoma, known for its spectrum of findings. 6 It may present as diffuse infiltration or as a nodular mass. Any area of the orbit may be involved, including the EOMs. The typical presentation is a fairly well-defined extraconal mass which has lobulated contours, is round-

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to-oval in shape, and may extend through the orbital fissures. 6 When it contacts the globe as a nodular mass, lymphoma tends to mold itself along the globe margin. 12 Significant contrast enhancement is not observed in orbital lymphoma. 6 The presence of bilateral orbital masses on an imaging study should raise the possibility of lymphoma. ~3 Conjunctival lesions present as anterior globe thickening, not distinguishable on imaging from lesions of the lid. 6 MR. On MR, orbital lymphoma usually presents as a hypointense lesion on both T1WI and T2WI (Fig 2). 6 The hypointensity on T2WI is thought to be secondary to the highly cellular nature of the neoplasm and may aid in differentiating lymphoma from other diseases. In contrast to the appearance on CT scans, moderate to marked enhancement is the rule of orbital lymphoma on post-contrast MR

KOELLER AND SMIRNIOTOPOULOS

images. 6 On CT or MRI, it is not possible to reliably distinguish pseudolymphoma from lymphoma based on the imaging appearance alone. 6'14 O t h e r I_yrnohoproliferative D i s o r d e r s In addition to lymphoma, other lymphoproliferafive disorders may also occur in the orbit. Burkitt's

lymphoma and granulocytic sarcoma (chloroma) present in the pediatric age group and, in contrast to lymphoma, frequently produce lyric bone destruction. In African children, granulocyfic sarcomas are second only to Burkitt's lymphoma as a cause of orbital neoplasms. 6

Angiolymphoid hyperplasia with eosinophilia (Kimura's disease) represents a reactive inflammatory process rather than a true neoplasm. 15 It is usually seen in the 4th to 7th decades and has a slight male predominance. 6 It presents as a wellcircumscribed, firm, reddish, hypervascular mass secondary to an abnormal proliferation of small blood vessels lined by vacuolated endothelial cells. These abnormal vessels are surrounded by chronic eosinophilic inflammation and scattered lymphoid follicles. In the late stages, marked fibrosis results. 6

Plasma cell proliferations (multiple myeIoma, plasmacytoma) account for about 0.5% of all orbital tumors. 16 These bulky, well-defined, soft tissue masses produce lyric defects in the orbital roof and lateral wall of the bony orbit without surrounding sclerosis. 16,17 Orbital involvement by leukemic infiltrates is unusual (Fig 3). In children, it is usually seen in acute myelogenous leukemia, whereas in adults, chronic lymphocytic leukemia is more common. 6 Involvement of the globe itself is not uncommon, with the choroid the most common site. is

kangerhans Cell Histiocytosis Clinical

Fig 2. Lymphoma. (A) Coronal T I W image without contrast shows a homogeneously wen-defined hypointense mass (m) of the inferior right orbit which displaces the inferior rectus muscle laterally. (B) Axial T2W image shows hypointensity of the mass compared with the signal intensity of fluid and similar to the signal intensity of gray matter. This relatively dark signal on T2W images is a characteristic feature of lymphoma and is secondary to the densely cellular matrix within the tumor,

Langerhans cell histiocytosis accounts for less than 1% of all orbital tumors. 19 Three types of the disease are known: eosinophilic granulorna (local form, 75%), Hand-Schuller-Christian disease (chronic recurring, 10% to 15%), Letterer-Siwe disease (widely disseminated, 10%). Usually arising in the superolateral; aspect of the bony orbit, hisriocytosis produces proptosis as the most common symptom however, patients may be asymptomaric. 19,2° As with other involvement of the skeletal system, the prognosis varies with the age of presentation and extent of disease? 1

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Fig 3. Leukemia, (A) Axial noncontrast CT shows a soft tissue mass of the lateral right orbit with extension into the middle cranial fossa. (B) Same image as (A) but with a bone window setting shows diastasis of the suture (arrow) and a permeative pattern of bone destruction.

Pathology Langerhans cellhistiocytosis is a reticuloendothelial disorder of unknown origin, but is suspected to be secondary to a breakdown in immune regulation with histiocytic proliferation and granuloma formation.22,23

Imaging The disease presents as an isodense to hyperdense soft tissue mass on noncontrast CT, with lytic bone destruction it usually enhances intensely after contrast administration (Fig 4). 22 On MRI, the mass is isointense to hypointense on T1WI and usually isointense to hypointense on T2WI. Occasionally, it may be hyperintense on T2WI. The presence of infundibular/hypothalamic enhancement in association with an orbital mass strongly suggests the diagnosis. 22

MESENCHYMAL NEOPLASMS Rhabdomyosarcoma

Clinical Rhabdomyosarcomas are the most common malignant orbital tumors in children, but are only 1/10th as common as retinoblastoma of the globe, n,22 Of all pediatric rhabdomyosarcomas, 10% involve the orbit primarily and 10% involve the orbit secondarily, either by metastasis or direct spread, n The peak age for presentation is 8 to 10 years old and 90% of cases occur in patients younger than 16 years of age. 1 These aggressive and invasive neoplasms produce rapidly progressive painless exophthalmos, proptosis, and ptosis of the upper lid31,22 Approximately 10% of patients have symptoms of mild headache or orbital pain. 24 About half arise behind the globe, 25% above the

Fig 4. Langerhans cell histiocytosis, (A) Axial noncontrast CT scan shows lytic bone destruction of the superolateral portion of left orbit by a soft tissue mass with enlargement of the left temporalis muscle, (B) Coronal noncontrast CT scan clearly depicts the extraconal nature of this lesion centered at the upper outer bony margin of the orbit.

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globe, 12% below the globe, and the remainder occur in either temporal or nasal locations, z4,25

Pathology Rhabdomyosarcomas are highly malignant and invasive neoplasms that arise from primitive mesenchymal elements. 1 There are four types, of which the embryonal form is by far the most common and which tends to involve sites other than the EOMs. Other types include pleomorphic, alveolar (worst prognosis), and differentiated (least common, best prognosis).24.25 On microscopic examination, these hypercellular tumors usually appear as sheets of small polyhedral and spindle-shaped cells with a high degree of mitotic activity arranged in loose fascicles. 22,26

Imaging Rhabdomyosarcomas present initially as homogeneous, well-defined masses but, secondary to rapid growth, subsequent extraorbital extension is frequently seen. 1 CT. On CT, these tumors are isodense with EOMs. Lyric or permeative bone destruction and enhancement are common features. = MR. On MR, the lesion is isointense to hypointense (similar to EOM) on T l W I and intermediate to hyperintense on T2WI (Fig 5). Variable enhancement has been reported after gadolinium injection. = Reflecting the highly vascular nature of these tumors, an intense blush is observed on angiographic studies.1

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Fibromatosis

Clinical Fibromatosis is the most common fibrous tumor of infancy. This locally infiltrating, but nonmetastasizing, neoplasm typically presents in the first 10 years of life. 27 It can be quite extensive and invasive. Although it may spontaneously involute, recurrences following local excision are common.

Pathology The mass is firm and rubbery on gross examination. Histologically, a hypercellular field of nonmalignant spindle-shaped cells is seen.

Imaging CT. Reflecting the infiltrative nature of the disease, fibromatosis presents as a poorly defined, heterogeneous mass which is isodense to muscle. Marked enhancement is usually seen. 28

Fibrous Histiocytoma Clinical Fibrous histiocytoma (FH) is the most common primary orbital mesenchymal tumor in adults. Still, it accounts for only 1% of all primary orbital neoplasms. The usual clinical presentation is one of gradual proptosis and diplopia secondary to a palpable mass. Chemosis and orbital congestion are common findings. Mean age of presentation is 42 years of age in benign FH and 53 years of age in malignant FH. 29 No gender predilection is seen. Approximately 40% of the cases involve the superior half of the orbit and a nasal location is more

Fig 5. Rhabdomyosarcoma. (A) Axial T I W image without contrast shows extensive soft tissue mass isointense to involving the lateral left orbit and left pterygopaiatine fossa with bone destruction, (B) Coronal T I W image without contrast shows extensive skull base destruction by this aggressive neoplasm.

ORBITAL MASSES

common than a temporal one. 26 Total surgical excision is the preferred treatment; radiotherapy has not been effective.

Pathology

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cal to that of a cavernous hemangioma (Fig 6). It may have a variable shape (round, lobular, or elongated) and may be either intraconal or extraconal in location. The lesion is isodense to brain parenchyma and variable enhancement is seen. Malignant forms may demonstrate bony destruction. In the absence of this finding, it is not possible to distinguish the benign from malignant forms on imaging a l o n e 9 ,31

On gross examination, FH masses present as firm to rubbery nodules which arise from the orbital fat. Cystic or myxoid changes may occur within the substance of the mass. Hemorrhage usually indicates malignant change. Microscopically, a mixed population of predominantly fibroblasts and, to a lesser extent, histiocytes are found. Based on gross and microscopic examination, FH is classified into three categories: benign (65%), locally aggressive (25%), and malignant (10%). 29 Benign lesions are well-circumscribed, small in size, and have regular nuclei with few or no mitotic figures. Locally invasive lesions are also small in size but have irregular borders and frequent mitotic figures. Malignant lesions have necrotic areas with a high degree of nuclear pleomorphism on histology.

Granulocytic sarcoma is associated with granulocytic leukemia and is most frequently seen in children (mean age of 7 years). The appearance of an orbital mass may precede the diagnosis of leukemia. The lesion may appear clinically as an inflammatory process that may delay diagnosis. Males are slightly more commonly affected. The disease occurs more commonly in Asians and Africans.

Imaging

Pathology

CT. On CT, FH presents as a well-circumscribed smooth mass, an appearance almost identi-

A discrete nodular mass arises in the orbit or lacrimal gland. Histologically, it is composed of

Granulocytic Sarcoma (Chloroma) Clinical

Fig 6. Malignant fibrous histiocytoma. (A) Axial noncontrast CT scan shows heterogeneous well-defined mass of the left lateral orbit, A biphasic appearance results from the more hyperdense component anteriorly contrasting with the hypodense portion more posteriorly. (B) Axial T2W image shows biphasic appearance with sharp demarcation between the two zones. Regions of hypointensity within the anterior compartment and the sharp line of hypointensity across the lesion suggest prior hemorrhage. Hemorrhage in a fibrous histiocytoma favors the malignant subtype. (C) Coronal T I W image without contrast shows hypointense mass occupying both intraconal and extraconal locations. The lateral rectus muscle is not well-delineated from the mass,

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immature blast cells filled with myeloperoxidase. When exposed to myeloperoxidase enzyme, the tumor produces a greenish color (hence the name, chloroma). 8

Imaging MR. Granulocytic sarcoma presents as a discrete or infiltrative mass that is hypointense to fat on T1WI and hyperintense to fat on T2WI. 31

Other Mesenchymal Orbital Lesions Several other rare tumors of mesenchymal origin occur in the orbit and will be briefly described. Primary orbital melanoma arises from native orbital melanocytes along the ciliary nerve, optic nerve leptomeninges, and scleral emissary vessels. If sufficient melanin is present within these wellcircumscribed masses, the diagnosis may be suggested by hyperintensity on T1WI. 1 Fibromas produce slowly progressive proptosis secondary to well-circumscribed homogeneous masses that are isodense to muscle. 1 Fibrosarcomas arise in children and in patients who have previously received radiation therapy. They present as an infiltrating lesion isodense to muscle (Fig 7). 32,33 Solitary fibrous tumor, more commonly seen in the pleura, may produce painless slowly progressive proptosis secondary to a well-circumscribed mass isodense to muscle. 34 Leiomyoma and leiomyosarcoma cannot be reliably distinguished by imaging alone, because both may present as well-circumscribed, usually intraconal masses. 35-37 The malignant leiomyosarcoma is usually diffusely infiltrative. 1 Lipo-

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mas are most common in the fifth and sixth decades, presenting as slowly progressive proptosis and diplopia. 38 These well-marginated nonenhancing lesions follow the signal intensity and attenuation of fat on imaging studies. 38 Liposarcomas present with rapidly progressive proptosis and decreased vision and have a either a cyst-like appearance or a diffusely infiltrative appearance on imaging studies. 39,4° Mesenchymal chondrosarcomas are seen predominantly in females from adolescence to middle adulthood, presenting as proptosis, periorbital pain, and ptosis. Patients have a poor prognosis with frequent recurrences and metastasis. 41 The presence of heavy calcification in a well-defined enhancing mass may provide a clue to the diagnosis on CT studies. 42 Granular cell tumor, more commonly observed in the tongue and subcutaneous tissues, may present as a well-marginated orbital mass isodense to brain parenchyma that commonly involves the EOMs and shows variable enhancement. 43 It may mimic Graves' disease. 44 Malignant rhabdoid tumor is a poorly understood neoplasm of early infancy to middle adulthood that may present as an intraconal mass and has a variable appearance on imaging studies .45 Alveolar soft part sarcoma is much more common in young women and presents as a well-defined mass with prominent enhancement. 46 Hemangiopericytoma is a locally aggressive intraconal or extraconal neoplasm producing slowly progressing proptosis. 8 It has a similar appearance to cavernous hemangioma on imaging studies with intense early enhancement. 31

Fig 7. Juvenile fibrosarcomao (A) Axial noncontrast CT scan shows retrobulbar mass which is isodense to the extracocular muscles and produces proptosis. It also indents the posterior margin of the globe. (B) Coronal T1W image without contrast shows homogeneously hypointense right orbital mass displacing the optic nerve inferiorly and medially and compressing the superior rectus muscle.

ORBITAL MASSES

VASCULAR LESIONS Cavernous Hemangioma

Clinical Hemangiomas, as a group, constitute the most common benign orbital tumor. 47 There are essentially two types: cavernous and capillary. Cavernous hemangiomas have a peak incidence between the second and fourth decades,48 although they are not uncommon in children. 1. Slowly progressive proptosis is the clinical hallmark of this lesion, which may also become larger upon the Valsalva maneuver (stress proptosis). Usually altered visual acuity is a late finding because the lesion tends to be infiltrative rather than compressive in nature. Occasionally, periorbital inflammatory changes may be present. In the younger age groups, it can be associated with hemangiomatosis. 47 Usually presenting as a bulky intraconal mass, it may also arise within the bony orbit (primary intraosseous hemangioma) and occur as an extraconal mass. 49

Pathology Cavernous hemangiomas are hamartomas contained within a fibrous capsule with large vascular channels filled with slowly moving blood. 26,47 No definite feeding vessels are identifiable5 3 They are usually intraconal but may also extend into the extraconal space or be exclusively extraconal. 5° Secondary changes include phleboliths, calcification, and fibrosis with hemosiderin deposition.13

Imaging CT. The typical appearance of a cavernous hemangiomas on noncontrast CT is asharply circumscribed, rounded, dense, intraconal mass. Extraconal extension is cominon. I4,47Intracranial extension occurs in 5% to 10% of cases, usually through the superior orbital fissure.47 Calcification (phlebolith) is almost pathognomonic for cavernous hemangioma. It is also seen in hemangiolymphangioma or as a late finding in capillary hemangiomas that do not involute spontaneously.47 Cavernous hemangioma may remodel, but should not produce, lytic destruction of the bony orbit. 13 On dynamic contrast-enhanced CT studies, there is relatively slow circulation of contrast through the tumor, resulting in variable degrees of enhancement in the early phase of injection. 5~ Within

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minutes, usually uniform, intense enhancement is observed, providing better definition of the true extent of the lesion. 47 Cavernous hemangiomas usually spare the orbital apex, which may distinguish these masses from those of optic nerve origin. 47 Even though cavernous hemangiomas are extensive vascular lesions, no arteriovenous shunting occurs and a normal-sized ophthalmic artery is usually seen. 47 MR. Cavernous hemangiomas are isointense or mixed on T l W I and isointense or slightly hyperintense on T2WI. 47 Following the dynamic CT pattern described previously, enhancement is virtually always present after gadolinium administration (Fig 8), 52

Capillary Hemangioma Clinical

Capillary hemangiomas, also known as infantile hemangioma, juvenile hemangioma, benign hemangioendothelioma and hemangioblastic hemangioma, are uncommon lesions, usually seen in the first year of life. 11 The vast majority involve the anterior portion of the orbit, commonly associated with cutaneous abnormalities (eg, port-wine stain) secondary to soft tissue infiltration.47 Typically, these lesions are flat, well-demarcated, and deeply colored.47The presence of diffusely dilated capillaries produces chemosis and excessive edema, al Rapid growth in the first 6 to 10 months of life is very common, usually followed by spontaneous involution in preschool years. 31,47 Occasionally, they may be associated with Sturge-Weber syndrome or other AVMs.53

Pathology Like the cavernous hemangioma, the capillary type is more infiltrative rather than compressive in nature, and it may extend intracranially through the optic canal or superior orbital fissure. 31 During the rapid growth phase, proliferation of endothelial cells occurs with multiple formed capillaries. 8 It is supplied by either the external carotid artery or internal carotid artery. Extensive hemorrhage is r a r e . 31

Imaging CT. Capillary hemangiomas are most commonly extraconal in location. They may be intracanal. 13 They have a variable appearance, present-

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Fig 8. Cavernous hemangioma. (A) Clinical photograph shows bluish discoloration of lateral canthus of left eye, Injected conjunctival vessels and ptosis are also present. (B) Coronal T I W image without contrast shows well-defined mass isointense to the extracocular muscles, It is predominantly located in the intraconal space. A small portion of it lies in the extraconal space. (C) Fat-suppressed coronal T l W image with contrast shows intense heterogeneous enhancement of the mass,

ing either as well-marginated or ill-defined masses. Intense enhancement, often with irregular borders, is typical. 31,47 MR. On MR, capillary hemangiomas have variable signal intensity thought to be related to slowly moving blood within capillary spaces supported by loose stroma and connective tissue. On T1WI, they show either isointensity or hypointensity and are isointense to hyperintense on T2WI. Marked hypointense areas may be noted on T2WI, representing flow voids and hemorrhage. The presence of flow voids distinguishes these hemangiomas from lymphangiomas. 47 Occasionally, thrombosis of the vascular channels and/or hemorrhage within the internal cavities may be seen. 47

kymphangioma Clinical Lymphangiomas are relatively infrequent orbital lesions, being less common than either of the other orbital vascular lesions, the capillary or cavernous hemangiomas. 8,11 They tend to occur in younger patients, from infants to young adults. ~1,47They are most commonly located within the intraconal space.

These benign lesions produce marked proptosis and diplopia secondary to the bulk of the mass. Optic nerve function is spared until late in the course.47Unlike the capillary hemangiomas, lymphangiomas slowly enlarge with age. 54 The slow growth of these encapsulated masses produces orbital expansion and remodeling rather than true bony destruction. 11 Sudden intratumoral hemorrhage, secondary to small blood vessels rupturing into the lymphoid tissue, is common and results in sudden propto sis. 8,11,47

Pathology Also known as cystic hygromas, lymphangiomas are composed of dilated lymphatic channels filled with clear fluid and surrounded by lymphoid tissue. 26 It is thought that they are the result of a sequestration of developing lymphatics that are also hemodynamically isolated. 4,11 They do not contain a capsule. 47 Because of the presence of lymphoid tissue, intermittent enlargement of these lesions in conjunction with concomitant viral infections may be observed. 26

ORBITAL MASSES

Imaging CT. Noncontrast CT scans demonstrate multiloculated, usually extraconal, dense masses, reflecting the common occurrence of hemorrhage into lymphatic channels. About half show enhancement after contrast administration. Usually this is less than that seen in hemangioma. Occasionally rimlike enhancement may be seen. 4,47 They may remodel bone. Calcification is a rare finding. 31Phleboliths do not occur in pure lymphangiomas, but may be seen in "mixed lesions" such as hemangiolymphangiomas. 47 MR. On MRI, lymphangiomas present as lobulated masses with variable signal intensity secondary to hemorrhage. 14 On T1WI, they are isointense to hypointense to fat, whereas on T2WI, they are usually hyperintense to fat. 14 Because of the presence of hemorrhage, fluid-fluid levels within the

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cystic spaces are not uncommon; however, flow voids are not a feature of lymphangiomas, which distinguishes them from the hemangiomas (Fig 9).47

Venous Varix

Clinical These rare vascular anomalies are not neoplastic but are simply a focal dilatation of orbital veins, which may be either small at rest and grossly enlarged upon increased venous pressure (eg, Valsalva maneuver) or constantly enlarged. 47,55,56

Pathology Orbital varices may be either congenital or acquired in origin. They may be associated with intraorbital or intracranial arteriovenous malformations or result solely from a congenital venous malformation or venous wall weakness. Phlebo-

Fig 9. Lymphangioma. (A) Clinical photograph shows proptosis of left orbit. (B) Axial T2W image shows extensive heterogeneous predominantly hyperintense mass of the left orbit. The mass appears compartmentalized and one compartment along the medial wall of the orbit has a fluid-fluid level (arrow) with the dependent portion being heterogeneously hypointense. (C) Axial T I W image without contrast shows fluid-filled compartment (arrow) with dependent portion also hypointense to the superior portion but to lesser degree than observed in (B), consistent with hemorrhage within this space, (D) Fat-suppressed axial T1W image with contrast at different level than seen in (B) or (C) shows extensive infiltrating and enhancing mass, which caused the proptosis.

284

liths may occur in the vascular channels. 8 Spontaneous thrombosis is common. 57

Imaging CT. A varix presents as a lobulated, densely enhancing mass often tubular in nature. Head position variation, Valsalva maneuver, or direct jugular venous compression may enlarge its size (Fig 10). 13,56Varices lack internal septations. 47 MR. A prominent flow void on spin-echo images or flow-related enhancement on gradientrecalled images is characteristic of orbital varices. 57

KOELLER AND SMIRNIOTOPOULOS

repetitive hemorrhage into a cholesterol granuloma. 58 It usually is observed in the orbital roof diploic space with subperiosteal extension into the lacrimal fossa. 47

Imaging A central nidus of blood-related signal intensities on T1WI and T2WI is the imaging hallmark of the hematic cyst. After contrast administration, it shows peripheral enhancement, probably secondary to a local inflammatory reaction). 47

Arteriovenous Malformation

Clinical Most orbital arteriovenous malformations (AVMs) involve the orbit by using orbital veins for drainage from larger intracranial lesions via the cavernous sinus. 47 Clinically, pulsatile proptosis with chemosis, lid edema, or bruit are commonly observed. Occasionally, they may be asymptomatic.

Imaging On either CT or MR, multiple tortuous vessels are present within the orbit, usually with communication to a larger intracranial AVM (Fig 11). Frequently, a dilated superior ophthalmic vein may be observed. Angiography best delineates the true extent of the lesion and facilitates accurate analysis for possible endovascular embolization.

Hematic Cyst

Clinical Similar to the petrous apex cholesterol granuloma, the hematic cyst is the result of chronic,

CONGENITAL/DEVELOPMENTAL LESIONS

Dermoid Cyst Clinical. Dermoid cysts represent the most common congenital lesion of the orbit and account for one-third of all childhood orbital tumors. 22,26 The superior temporal quadrant at the frontozygomatic suture is the most common location, followed by the upper nasal orbit at the frontoethmoidal suture. 22 Exhibiting slow growth and isolated from the EOMs or optic nerve, they usually do not cause visual symptoms. Pathology. Dermoid cysts arise as a developmental sequestration of the ectoderm within the suture lines or diplre of the orbital bones. This explains the close relationship of these lesions with the sutures of the orbit. Imaging. Dermoid cysts usually follow either fat or fluid signal and occasionally may show calcification (Fig 12). They erode and remodel the

Fig 10. Orbital varix. (A) Axial contrast-enhanced CT scan without Valsalva manuever shows no abnormality within right orbit. (B) Repeat scan after Valsalva manuever shows prominent enhancing mass located in retrobulbar fat.

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285

Fig 11. Arteriovenous malformation. (A) Noncontrast axial CT scan shows extensive soft tissue mass of left orbit with marked proptosis and extension into temporal subcutaneous tissues. (B) Coronal T I W image without contrast shows soft tissue mass involving both intraconal and extraconal spaces of the left orbit. A grossly dilated superior ophthalmic vein is seen (arrow). (C) Lateral view from left internal carotid artery injection (arterial phase) shows classic appearance for AVM, supplied by enlarged ophthalmic artery as primary feeding vessel.

bony orbit but do not produce lytic bone destruction. 22A fat-fluid level may be seen on MRI studies. A much less common congenital orbital lesion, the orbital teratoma, presents as a multiloculated, cystic mass with solid areas, producing a more complex signal pattern than dermoid cysts. They may be quite large, even at birth. 59 METASTASIS TO THE ORBIT

Clinicopathology

Fig 12. Epidermal inclusion cyst. Noncontrast coronal CT scan shows well-marginated hypodense mass (arrow) with fluid attenuation located in the upper nasal quadrant of the left orbit. The mass was easily removed as a single mass. Histological analysis revealed keratinizing squamous lining without epidermal appendages, consistent with epidermal inclusion cyst rather than dermoid cyst. The imaging appearance is identical to that which may be seen in orbital dermoids.

Metastasis to the orbit accounts for approximately 10% of all orbital neoplasms. 6° Half are caused by secondary spread from adjacent structures (globe, sinuses, oropharynx) and half from hematogenous spread from distant primary tumors. 8 The incidence of these lesions is increasing because of longer survival now seen with the advent of better therapies.~ Breast carcinoma (42%) is by far the most common tumor to spread to the orbit. This is followed by lung carcinoma and the unknown primary cancer (both at 11%), prostate carcinoma (8%), and melanoma (5%). 1 A metastatic orbital tumor was the presenting sign of an

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unsuspected malignancy in one-third of cases in one series. 61 Certain primary malignancies tend to present with orbital metastases earlier than others; this group includes gastrointestinal, renal, and lung primaries. 1 The average survival after an orbit metastasis is diagnosed is dismal, at 9 months. ~Better survival is observed with prostate, thyroid, carcinoid, and breast primaries. 6° At the opposite end of the spectrum, skin melanoma metastasizing to the orbit is indicative of fulminant disease with poor progno-

sis.62 Within the orbit, metastatic disease is more common to the retrobulbar fat and bony structures than to the extraocular muscles. 63 As a consequence, it usually causes a rapid painful exophthalmos. 13 Diplopia, ptosis, eyelid swelling, pain, and vision loss may also be observed. 63-65 A notable exception to this presentation is enophthalmos seen with scirrhous carcinoma metastasis, such as breast carcinoma. 66 If the lesion is palpable, it is usually firm to the touch, reflecting the infiltrative nature of metastasis.

Pediatric Metastatic Disease In the pediatric population, metastatic orbital disease is less common than primary orbital tumors. 11 Metastatic neuroblastoma is second only to primary refinoblastoma as the most frequent malignant tumor in childhood. 67 Neuroblastoma metastasis usually occurs in patients younger than 2 years of age and is observed in 20% of cases. Spiculated thickening of the bony orbit n is commonly seen within 3 months of the initial diagnosis. 67 Half of these lesions arise from an adrenal gland primary, followed by those arising from the retroperitoneal space (25 %), the mediastihum (10%), and the neck (2% to 5%). 15The lesions are frequently hemorrhagic and therefore have a mixed appearance on imaging studies. The zygoma and adjacent temporal bone are the most commonly involved orbital bony structures. 68 Another common cause of pediatric orbital metastases is Ewing's sarcoma, which presents most commonly in the second decade and may metastasize to the bony orbit. 11 The hemorrhagic nature of this malignancy explains its common clinical presentation of sudden proptosis. 1

KOELLER AND SMIRNIOTOPOULOS

Imaging CT. Metastatic lesions to the orbit usually present as irregularly shaped masses on noncontrast CT which are isodense to muscle. 13,69,7° With contrast injection, they show slight enhancement. 69 Bone destruction is a common finding, being present in two-thirds of patients. 71 The majority (60%) are extraconal in location, whereas 20% are intraconal and 20% have a diffuse appearance. The presence of concomitant intracranial metastasis, either with direct extension or separated, is quite common, seen in approximately 66% of cases. Prostate carcinoma metastasis may be osteoblastic, involving the bony orbit. It may also present as an orbital soft tissue mass without bone involvement. 72 Metastatic disease to the lacrimal gland usually produces diffuse gland enlargement that is indistinguishable from primary lacrimal gland lesions by imaging methods alone. 7° Metastatic disease to the extraocular muscles (EOMs) is uncommon; only about 7% of cases of EOM enlargement are secondary to metastasis. 73 However, when isolated lateral rectus muscle enlargement is observed on an imaging study, either pseudotumor or metastasis should be suspected until proven otherwise3 MR. On MRI, metastatic disease is usually hypointense to fat on T1WI and hyperintense to fat on T2WI. This appearance may help to differentiate it from pseudotumor, which is usually isointense to fat on T2WI. 1,13 When hyperintense lesions are seen on TIWI, a very vascular metastasis (eg, thyroid, renal) or melanoma metastasis should be suspected. 13 Metastatic lesions frequently enhance (Fig 13). 1

LACRIMAL GLAND LESIONS The lacrimal gland can be thought of as the "50% gland," because half of the masses that occur there are epithelial neoplasms and the other half are caused by lymphoproliferative or inflammatory disease (Fig 14). 74 Furthermore, the epithelial neoplasms are evenly divided between those that are benign and those that are malignant. The clinical diagnosis of a lacrimal mass is not difficult, because they present as a palpable mass of the upper outer quadrant or proptosis. If pain is present, it usually indicates an adenoid cystic carcinoma with perineural invasion.1

ORBITAL MASSES

287

Fig 13. Carcinoid metastasis to the orbit. (A) Fat-suppressed axial T l W image without contrast shows retrobulbar mass (arrow) which is isointense to gray matter. (B) Fat-suppressed axial T l W image with contrast shows intense enhancement of the lesion. Biopsy revealed carcinoid tumor. Abdominal CT scan and barium studies {not shown) demonstrated tethered folds within the small bowel secondary to fibrosis from the primary lesion.

Epithelial Carcinoma Epithelial carcinoma compose half of all lacrimal epithelial neoplasms. In this group are adenoid cystic carcinoma (discussed in the following section), malignant mixed cell tumor, mucoepidermoid carcinoma, squamous cell carcinoma, undif-

ferentiated (anaplastic) carcinoma, and sebaceous carcinoma.74, 75

Adenoid Cystic Carcinoma Clinical. Adenoid cystic carcinoma is the most common malignant epithelial neoplasm of the

Fig 14. Lymphoma of the lacrimal gland. (A) Axial TIW image without contrast shows a homogeneous well-defined mass of the left lacrimal gland. The signal intensity of the mass is identical to that of the normal right lacrimal gland {*). (B) Axial proton-density image shows slight hypointensity of the mass compared with the signal intensity of the right lacrimal gland. (C} Coronal T l W image with contrast shows homogeneous mild enhancement of the mass (m).

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lacrimal gland. Its propensity for perineural invasion at least partially explains why it has a poor 5-year survival (21%). Death is usually secondary to intracranial extension. Pathology. The tumor derives its name from the histological appearance of tightly packed cells around large ovoid spaces. Imaging. Adenoid cystic carcinoma has two appearances on imaging studies. It may present as a well-defined mass or as an infiltrative form with intraorbital invasion. Lytic destruction along the lateral orbital wall may be seen. Calcification within a lacrimal mass raises the possibility of adenoid cystic carcinoma. 76 The MRI appearance is nonspecific with hypointensity on TlWI and hyperintensity on T2WI. Other malignant primary lacrimal gland tumors have similar imaging features, which makes it difficult if not impossible to distinguish them from each other. A notable exception is the mucoepidermoid carcinoma, which shows marked enhancement on CT and typically is hyperintense on TIWI images)

Benign Mixed Tumor (Pleomorphic Adenoma) Clinical. Benign mixed tumors of the lacrimal gland account for half of all epithelial neoplasms. Pathology. There are two cell populations on histological examination: ductal epithelial cells and metaplastic epithelium forming a variable matrix (myxoid, fibrous, and cartilaginous)Y The masses are pseudoencapsulated. They may have cystic spaces. Imaging. Imaging reflects the variable pathology. A benign mixed tumor presents as a well-

KOELLER AND SMIRNIOTOPOULOS

marginated mass. It may remodel the bony orbit, but should not destroy bone. They show minimal to moderate enhancement. 77 The appearance on MRI is nonspecific (Fig 15). 76

LACRIMAL SAC MASSES

Clinical Lacrimal sac masses are relatively rare lesions. Males are twice as commonly involved as women. % The lacrimal sac masses may present from early childhood to elderly years, with a peak incidence of 20 to 60 years of age. 78 Epiphoria is the most common symptom, followed by nasal obstruction, epistaxis, and purulent discharge. 78 Duration of symptoms is usually from 2 to 12 months. 78 Benign lesions tend to be well-circumscribed, freely mobile, and resilient on palpation. Malignant lesions, which compose the majority (90%) of lesions in this area, are characterized by rapid growth, skin fixation and firm texture, and almost one-third of patients with such disease will have regional adenopathy (eg, preauricular, submandibular, cervical nodes) .79 Benign tumors involving the lacrimal sac include polyps, fibroma, fibrous histiocytoma, oncocytoma, and oxyphillic adenoma. These lesions are often confined to the lumen of the lacrimal sac, shown as a simple filling defect on dacrocystography. On the other hand, the finding of extraluminal extension on dacrocystography suggests malig-

Fig 15. Benign mixed tumor of the lacrimal gland. (A) Coronal T1W image with contrast shows well-defined mass (arrow) in the region of the right lacrimal gland with heterogeneous features. Some remodeling of the adjacent bony orbit is seen. (B) Axial proton-density image shows mild hyperintensity of the mass (arrow).

ORBITAL MASSES

289

Fig 16. Fibrosarcoma. (A) Noncontrast axial CT scan shows soft tissue mass (arrow) centered in the region of the left lacrimal sac with destruction of the adjacent bone, (B) Noncontrast coronal CT scan shows the mass extending into the nasolacrimal duct and the inferomedial orbit where it displaces the globe laterally,

nancy. Malignant tumors of the lacrimal sac include carcinoma (with squamous cell carcinoma being the most common), malignant melanoma, hemangiopeficytoma, lymphoma, fibrosarcoma, and metastasis (Fig 16). Other carcinomas of the lacrimal sac region include transitional carcinoma, adenoid cystic carcinoma, oncocyfic adenocarcinoma, and mucoepidermoid carcinoma. 79 Lymphoma seen in the lacrimal sac region typically arises from the ethmoid sinuses and involves the sac by direct extension. 79 A mucocele from the ethmoid sinuses is the most common secondary lesion to involve the lacrimal sac region, s°

Imaging CT. Because these lesions are easy to detect clinically, the role of imaging is to define the center,

margins, and signal characteristics of the mass, including remodeling of adjacent bone and extension into the paranasal sinuses (Fig 16). A mucocele has fluid attenuation with a smooth wall, unless it is inflamed, in which case it has an irregular wall. Carcinomas usually present as a large mass with irregular margins and bone destruction (Fig 17). Most tumors are homogeneous, isodense to muscle, without specific imaging features for a specific histopathologic diagnosis. 6 SUMMARY

Using a "space approach" to orbital masses combined with an analysis of its signal intensities often allows the radiologist to limit the differential diagnosis for these lesions to just a few possibili-

Fig 17. Mucoepidermoid carcinoma of the lacrimal sac. (A) Axial contrast-enhanced CT scan shows soft tissue mass centered in the right lacrimal sac region displacing the right inferior rectus muscle laterally. (B) Axial CT scan with bone w i n d o w at more inferior level than shown in (A) shows bone destruction adjacent to the mass. The right nasolacrimal duct cannot be identified secondary to the destruction. The normal left nasolacrimal duct is shown by the arrow.

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KOELLER AND SMIRNIOTOPOULOS

ties. T h e c o r o n a l p l a n e o n i m a g i n g studies is u s u a l l y t h e single b e s t p l a n e o n w h i c h to define f r o m w h a t s p a c e a m a s s arises. R e m o d e l i n g o f b o n e is n o t u n c o m m o n in s l o w l y g r o w i n g m a s s e s ; h o w ever, true b o n e d e s t r u c t i o n s h o u l d s u g g e s t a m a l i g -

n a n t process. P e r h a p s the s i n g l e m o s t i m p o r t a n t role t h e r a d i o l o g i s t p l a y s i n o r b i t a l i m a g i n g is to i d e n t i f y t h e true e x t e n t o f the lesion. T h i s i n f o r m a t i o n f r o m i m a g i n g studies is e s s e n t i a l f o r o p t i m a l presurgical planning.

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