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Orbit



Orbit





INTRODUCTION

Orbital disease is relatively uncommon, but quite diverse in nature. Inflammatory diseases, such as infectious cellulitis, and the immunological disorders thyroid ophthalmopathy and idiopathic orbital inflammation or “pseudotumor” are encountered most often in general clinical practice. However, the soft tissues of the orbit occasionally give rise to a relatively broad spectrum of primary neoplasms, and the orbit can be involved secondarily by systemic lymphoma, metastases from distant primary cancers, or by tumors that arise in neighboring tissues such as conjunctiva, eyelid, paranasal sinuses, or even the intracranial cavity (Fig. 14-1).

The essential clinical manifestation of orbital disease is ocular proptosis or exophthalmos (Fig. 14-2A). The eye usually is pushed forward because the orbit is a semiconfined space bounded by bony walls, and most orbital diseases are space occupying. The proptotic eye may be pushed directly forward (axial proptosis) or in other directions (i.e., down and in) that are determined by and serve to indicate the location of the orbital lesion. For example, tumors of the lacrimal gland, which is located in the superotemporal orbit, typically push the eye inferomedially as well as forward, while mucoceles of the ethmoid sinus in the medial orbital wall cause lateral displacement. Retraction of the eye or enophthalmos occurs occasionally. Causes of enophthalmos include traumatic blow-out fractures of the orbital floor and sclerosing tumors such as metastatic scirrhous breast carcinoma. Other symptoms and signs of orbital disease include pain, loss of vision, and ocular motility disturbances, which may or may not be conspicuous depending on the underlying cause; some orbital tumors, that is, lymphomas, tend to be well tolerated. Others, that is, metastatic carcinoma, are more likely to be symptomatic.


ORBITAL INFLAMMATORY DISEASE

Most orbital disease encountered by the ophthalmologist in general practice is inflammatory in nature. The most common inflammatory diseases of the orbit include infectious orbital cellulitides, noninfectious idiopathic orbital inflammation (inflammatory orbital pseudotumor), and Graves disease or thyroid orbitopathy.

Orbital cellulitis usually is caused by the extension of a primary sinus infection into adjacent soft tissues of the orbit (Fig. 14-3). Abscesses can form beneath the periosteum (subperiosteal abscess) or in the orbital soft tissues. Patients with orbital cellulitis have signs of acute inflammation including erythema and pain as well as proptosis. Although most orbital cellulitis is caused by bacteria, fungi such as Aspergillus or Mucor occasionally invade the orbit from primary foci in the sinuses. Haemophilus influenzae is an important cause of orbital cellulitis in children but is becoming rarer due to immunization. Rarely, a clinical picture resembling orbital cellulitis may be caused by an extensively necrotic intraocular retinoblastoma or melanoma. Orbital involvement has been reported in allergic fungal sinusitis (Fig. 14-4).

Mucormycosis is a potentially lethal opportunistic infection by saprophytic fungi that usually occurs in acidotic persons such as those with poorly controlled diabetes. The fungus is vasotropic and invades orbital vessels causing thrombosis and necrosis (Fig. 14-5). Histopathology shows both acute and chronic granulomatous inflammation and necrotic tissue. The hyphae are large and nonseptate and are easily identified in standard hematoxylin and eosin (H&E)-stained sections. Lives occasionally can be saved if an expedient diagnosis is made and antifungal therapy is instituted.






FIG. 14-1. Orbital contents. The orbital contents include the eye, optic nerve, smooth and striated muscle, vessels, nerves, fatty and fibrous connective tissue, and the lacrimal gland. They are delimited anteriorly by a fibrous tissue septum and protected by the eyelids.

Thyroid eye disease (thyroid ophthalmopathy, Graves orbitopathy) is the most common cause of unilateral or bilateral exophthalmos (Fig. 14-2A). Affected patients have an underlying immunological disorder, which is complex and still poorly understood, that affects both the thyroid gland and orbital structures, especially the extraocular muscles. The exophthalmos is caused by enlargement of the extraocular muscles (Fig. 14-2B,C). The enlarged muscles contain foci of chronic nongranulomatous inflammation and increased quantities of glycosaminoglycans and

show endomysial fibrosis (Fig. 14-2D). The tendon of the extraocular muscle and the orbital fat characteristically are noninflamed, a feature that serves to differentiate thyroid ophthalmopathy from idiopathic orbital inflammation (pseudotumor). Visual loss due to compressive optic neuropathy occurs in some patients when the swollen muscle bellies press on the optic nerve in the crowded orbital apex. Corneal complications caused by exposure can also cause visual loss. Graves ophthalmopathy can occur in patients whose thyroid function tests are high, low, or even normal. Most cases are readily diagnosed by the demonstration of enlarged extraocular muscles on computed tomography (CT) or MRI scans. Very few cases are biopsied.






FIG. 14-2. A. Thyroid ophthalmopathy (Graves disease). The patient has bilateral exophthalmos and a characteristic stare. Vertical extraocular muscle imbalance (right hypotropia) reflects fibrosis of right inferior oblique muscle. B. CT shows massive enlargement of extraocular muscles. C. Postmortem exenteration specimen from a patient with thyroid optic neuropathy shows massive enlargement of extraocular muscles. D. Extraocular muscle from case seen grossly in (C) contains patchy foci of chronic inflammatory cells composed largely of lymphocytes. The myofibers are separated by fibrosis. The inflammation in Graves disease characteristically spares the tendons of the extraocular muscles and the orbital fat, features that serve to distinguish the disorder histopathologically from idiopathic orbital inflammatory pseudotumor. (C. Photo by the author. From Hufnagel TJ, Hickey WF, Cobbs WH, et al. Immunohistochemical and ultrastructural studies on the exenterated orbital tissues of a patient with Graves’ disease. Ophthalmology 1984;91:1411-1419. Courtesy of Ophthalmology, D. H&E ×50.)






FIG. 14-3. Orbital cellulitis. A. CT scan of patient with orbital cellulitis shows opacification of adjacent infected sinus. Orbital cellulitis often is caused by extension of a primary sinus infection into orbital soft tissues. B. Orbital abscess. An abscess is a focal collection of polymorphonuclear leukocytes. Many of the polys infiltrating the orbital fat are degenerated. Basophilia reflects necrosis. (A. Photo courtesy of Jurij Bilyk, MD, Wills Eye Institute, B. H&E ×100.)

Idiopathic orbital inflammation or pseudotumor is relatively common (Fig. 14-6A,B). Although orbital pseudotumor undoubtedly is an immunological disorder, the details of its immunopathology and the identity of the antigens responsible for inciting the inflammation are still unclear. Idiopathic orbital inflammatory pseudotumor is a diagnosis of exclusion, from both the clinical and histopathological standpoint. The presence of fungi, bacteria, and acid-fast organisms, foreign substances, and other specific inflammatory diseases such as granulomatosis with polyangiitis (GPA; Wegener) or sarcoidosis must be excluded with special stains or appropriate tests.






FIG. 14-4. Allergic fungal sinusitis. A. CT scan shows massive involvement and expansion of sinuses by allergic mucin. B. Allergic mucin contains clumps of eosinophils and Charcot-Leyden crystals (arrow). C. GMS stain discloses hyphae of noninvasive fungus within mucin. (B. H&E ×250, C. Gomori methenamine silver ×250.)






FIG. 14-5. Mucormycosis. A. Necrotic orbital fat contains large branching hyphae. The hyphae are readily seen in routine H&E sections. B. Fungus infiltrates wall and lumen of thrombosed vessel. (A. H&E ×250, B. H&E ×100.)

Idiopathic orbital inflammation can affect both adults and children who may have either unilateral or bilateral disease. Although occasional cases are relatively asymptomatic and indolent in their course, idiopathic orbital inflammation classically presents explosively with the acute onset of pain, ocular proptosis, muscle paresis, and sometimes visual loss. The inflammation may be localized to single orbital structures such as the extraocular muscles (orbital myositis), the lacrimal gland (chronic dacryoadenitis), or the sclera or episclera (scleritis or episcleritis). A diagnostic trial of systemic corticosteroids may be administered to patients suspected of having idiopathic orbital
inflammation, because the disorder is exquisitely sensitive to steroids.

Biopsy is often performed on patients with orbital inflammatory pseudotumor. Microscopy typically discloses a polymorphous infiltrate of inflammatory cells that may contain lymphocytes, plasma cells, eosinophils, macrophages, and occasionally epithelioid histiocytes (Fig. 14-6A,B). Although vessels ringed or cuffed by chronic inflammation can be seen, this reflects diapedesis of lymphocytes, not true vasculitis. Lymphoid follicles and germinal centers occur in some cases, and fibrosis is often extensive. If the lacrimal gland is involved, its acini are destroyed by the inflammatory process and fibrosis replaces the parenchyma. The fibrosis is responsible for the typically eosinophilic appearance of specimens under low magnification light microscopy (Fig. 14-6B). This eosinophilia usually distinguishes “pseudotumor” from lymphoid tumors, which are composed of sheets of basophilic cells. Follicular lymphoid hyperplasia is considered to be an orbital lymphoid tumor by ophthalmic pathologists; it should not be called an inflammatory pseudotumor.






FIG. 14-6. A. Idiopathic orbital inflammation, orbital fat (idiopathic inflammatory pseudotumor). The orbital fat contains patchy foci of chronic inflammatory cells. The polymorphous inflammatory infiltrate was composed largely of lymphocytes and plasma cells. B. Idiopathic orbital inflammation with fibrosis, lacrimal gland (sclerosing idiopathic inflammatory pseudotumor). A few residual ductules persist in the eosinophilic, chronically inflamed scar tissue that has replaced the lacrimal gland. Patchy foci of chronic inflammatory cells are present. Higher magnification disclosed a polymorphous inflammatory infiltrate composed largely of lymphocytes and plasma cells. C. Sarcoidosis. Atrophic parenchyma of lacrimal gland contains multiple discrete noncaseating granulomas consistent with sarcoidosis. D. Granulomatosis with polyangiitis (Wegener). Granulomatous vasculitis involves orbital vessel. Foci of necrosis were present. (A. H&E ×25, B. H&E ×25, C. H&E ×50, D. H&E ×50.)

The sclerosing type of orbital pseudotumor may be a subset of IgG4-related disease (Fig. 14-7). It has been estimated that 40% of patients with idiopathic orbital inflammation have IgG4-related disease. The topic of IgG4-related disease is somewhat confusing, and criteria for diagnosis are not clear-cut. Classic diagnostic criteria in tissue biopsies include an intense lymphoplasmacytic infiltrate with lymphoid follicles, obliterative phlebitis, and often eosinophilia. Storiform fibrosis and obliterative phlebitis are said to be rare in orbital disease, however. There also are conflicting statements about the number of IgG4 plasma cells that are required for diagnosis. Demonstration of IgG4-positive plasma cells requires immunohistochemical stains for IgG4 and IgG (Fig. 14-7D). It is often stated that the ratio of IgG4/IgG plasma cells should be at least 40%. The actual intensity of the IgG4-positive plasma cell infiltrate is less clear. Ten or more IgG4-positive plasma cells per high-power
field is a frequently stated criterion. However, some authors require much higher counts, that is, 100/HPF for lacrimal gland involvement. The issue is complicated further by the observation that IgG4-positive plasma cells are common in orbital tissue from patients with variety of other inflammatory disorders including sarcoidosis and GPA. Patients found to have IgG4-related disease in the orbit should be investigated for involvement of other organs, because early treatment may prevent destructive changes.

If true vasculitis, granulomatous inflammation, and focal necrosis are observed, the patient may have GPA, formerly called Wegener granulomatosis (Fig. 14-6D). About one third of patients with GPA have ophthalmic manifestations during the course of their disease, and they may present with ocular findings such as orbital infiltration or peripheral corneal ulceration. Clinical suspicion is important because the classic histopathologic features of GPA are found in few orbital biopsies. Most patients have concurrent sinus disease. The cytoplasmic antineutrophilic cytoplasmic antibody (c-ANCA) test is a helpful diagnostic adjunct but may be negative in the early stages of the disease.

Lacrimal gland biopsy typically discloses discrete noncaseating granulomas composed of epithelioid histiocytes and giant cells in sarcoidosis, which is another diagnosis of exclusion (Fig. 3-10A). Lacrimal gland biopsy occasionally is performed to confirm the diagnosis of sarcoidosis histopathologically.

Unusual inflammatory reactions related to the iatrogenic use or instillation of various materials occasionally are encountered in the eyelids, conjunctiva, or orbit. These substances include proprietary formulations of collagen or hyaluronic acid used as dermal fillers in cosmetic surgery and silicone oil used to tamponade the retina during vitreoretinal surgery. Leaking silicone oil stimulates lipogranulomatous inflammation that contains large vacuoles of oil and vacuolated histiocytes (Fig. 14-8).






FIG. 14-7. IgG4-related disease, orbit. A. Orbital biopsy comprises intense follicular lymphoid hyperplasia and area of fibrosis at right. B. Area of storiform fibrosis contains numerous plasma cells and eosinophils, shown at higher magnification in (C). D. Many of the plasma cells (>100/HPF) are immunoreactive for IgG4. (A. H&E ×10, B. H&E ×50, C. H&E ×400, D. IHC for IgG4 ×250.)



ORBITAL TUMORS

A wide variety of benign and malignant primary neoplasms are spawned by the tissues of the orbit. Most of these tumors are relatively rare. Secondary involvement of the orbit by blood-borne metastases, systemic lymphoproliferative disorders, or direct invasion from contiguous structures also occurs. Children and adults are affected by different spectra of orbital tumors.


Orbital Tumors in Adults

Primary orbital tumors that are encountered fairly often in adults include cavernous hemangioma or malformation; schwannoma; solitary fibrous tumor (SFT), which includes tumors previously diagnosed as fibrous histiocytoma (FH) or hemangiopericytoma; epithelial tumors of the lacrimal gland; and lymphoid tumors. Cavernous hemangioma and lymphoid tumors are encountered most often.


LYMPHOID TUMORS

Orbital lymphoid tumors constitute a spectrum that includes polyclonal reactive lymphoid hyperplasias and malignant lymphomas composed of clonal proliferations of lymphoid cells (Figs. 14-9 and 14-10). Immunophenotypic analysis has shown that most lesions previously classified light microscopically as atypical lymphoid hyperplasias are low-grade lymphomas. Lymphoma is also discussed in Chapter 5.






FIG. 14-8. Orbital silicone oil granuloma after vitreoretinal surgery. A. Excised orbital tissue contains large vacuoles of silicone oil. B. Single encapsulated vacuole. C. Orbital tissue contains large empty vacuoles with intervening infiltrate of macrophages that have ingested oil, seen at higher magnification in (D). (C. H&E ×250, D. H&E ×250.)

Orbital lymphoma usually is a disorder of older patients that is diagnosed on average at age 60 years. The onset of orbital lymphoma is usually insidious. Orbital lymphoid tumors typically present with painless, well-tolerated proptosis, because the tumor has no fibrous stroma, is soft and pliable, and molds to the globe and other orbital structures. Some patients may present with a conjunctival mass or patch of salmon-colored tissue on the epibulbar surface or fornix (Figs. 5-32A,B and 14-9A). The tumor’s characteristic
salmon hue reflects the presence of many fine capillaries. The lymphoid infiltrate is often delimited sharply by tissue planes. The latter are evident on imaging studies as linear margins. Lymphomas diffusely infiltrate and thicken the lacrimal gland, which drapes around the globe assuming an appearance that Jakobiec has facetiously termed a “pregnant pancake.” The latter contrasts with epithelial neoplasms of the lacrimal gland, which typically are rounded. Ninety percent of orbital lymphomas involve the superior part of the orbit behind the orbital septum. More than 40% involve the lacrimal gland and often affect its palpebral lobe. Bone destruction is very rare except in multiple myeloma. When extraocular muscles are involved, usually a single muscle is affected. Motility remains normal because the lymphoma does not stimulate fibrosis.






FIG. 14-9. Lymphoid tumors. A. Cut surface of soft orbital lymphoma has uniform salmon-yellow color. B. Follicular lymphoid hyperplasia. Small well-differentiated lymphocytes surround a germinal center. The lighter cells in the germinal center are tingible body macrophages, which are antigen-presenting cells. Mitoses normally are found in germinal centers. The germinal center and adjacent mantle zone are composed largely of B lymphocytes. C. Diffuse non-Hodgkin lymphoma, well-differentiated lymphocytic type. Infiltrate is composed of monotonous monomorphic sheet of small well-differentiated lymphocytes. Immunophenotypic studies disclosed a monoclonal population of B lymphocytes. D. Diffuse large cell lymphoma. This obviously malignant tumor is composed of large, atypical immunoblastic B cells that have prominent nucleoli. Apoptotic cells and mitoses are present. (B. H&E ×100, C. H&E ×250, D. H&E ×250.)

Ocular lymphomas are extranodal by definition because the orbit lacks lymphatics and lymph nodes, and most are diffuse, as well. About two thirds of ocular adnexal lymphoid tumors are malignant non-Hodgkin lymphomas (NHL) composed of a monoclonal proliferation of B lymphocytes, and most of these are low-grade lesions composed of well-differentiated lymphocytes. In recent years, pathologists have used the WHO classification to classify lymphomas. Types of NHL in the WHO classification that typically affect the ocular adnexa include extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (often called MALT lymphoma), follicular lymphoma, mantle cell lymphoma, diffuse large cell lymphoma, and small lymphocytic lymphoma (SLL) (Fig. 14-9C,D).

More than half of ocular adnexal lymphomas are MALT lymphomas. About 23% are follicular lymphomas, 5% mantle cell, and 4% small lymphocytic lymphoma (SLL/CLL). These four entities are very difficult to differentiate using routine light microscopy alone, but distinguishing them is important clinically because they differ greatly in prognosis and the proper choice of therapy requires accurate classification. The cells of extranodal marginal zone or MALT lymphoma are CD20 positive but are negative for
CD3, CD5, and CD10 (Fig. 14-10A). Mantle cell lymphoma is usually widely disseminated on presentation and has a poor prognosis. Its CD20-positive B cells coexpress T-cell marker CD5 and BCL-1 (also called cyclin D1) (Fig. 14-10B). The cells constituting the neoplastic follicles of follicular lymphoma stain with CD20, CD10, and BCL-2 (Fig. 5-34). About one third of patients who have orbital lymphomas have a past history of, or will develop, systemic lymphoma. All patients with ocular adnexal lymphoid tumors need to be evaluated by a hematologist-oncologist. Some patients with polyclonal lymphoid proliferations are a risk for systemic lymphoma.

Lymphoid tumors of the orbit and ocular adnexa are treated with external beam radiotherapy, chemotherapy, and immunotherapy with agents such as rituximab, a monoclonal antibody directed against B lymphocytes. External beam radiotherapy with appropriate eye shielding can be used if there is no evidence of systemic disease. Chemotherapy or immunotherapy should be used if extraocular systemic lymphoma is present. This may be supplemented with adjuvant radiotherapy if ocular regression is subtotal.






FIG. 14-10. A. Extranodal marginal zone lymphoma of MALT lymphoma. Lymphoma is composed of diffuse infiltrate of small, well-differentiated B lymphocytes. Immunohistochemical panel at the right shows that neoplastic B cells express B cell marker CD20 but are negative for CD3, CD5, and CD10. More than half of ocular adnexal lymphomas are MALT lymphomas. B. Mantle cell lymphoma. The neoplastic B cells constituting mantle cell lymphoma usually have irregular cleaved nuclei. The CD20-positive B cells coexpress T-cell marker CD5 but are negative for CD3. Positive immunoreactivity for BCL-1 (cyclin D1) confirms the diagnosis. Mantle cell lymphoma has a poor prognosis. (A. Main figure: H&E ×250, insets: IHC for CD20, CD3, CD5, and CD10, all ×100; B. Main figure: H&E ×250, insets: IHC for CD20, CD3, CD5, and BCL-1, all ×100.)


VASCULAR LESIONS

Cavernous hemangioma or malformation is probably the most common primary orbital tumor (Fig. 14-11). These lesions recently have been categorized as nondistensible venous malformations. Cavernous hemangiomas typically occur in middle-aged women. They cause low-grade proptosis and usually are well tolerated, sparing vision and ocular motility. Some cases are discovered incidentally when imaging is performed for headache or other indications. These benign vascular tumors are well-circumscribed, encapsulated lesions with a pebbly surface that appear dusky red or purplish-blue grossly (Fig. 14-11B). They are composed of large round or oval vascular spaces lined by endothelium, which are separated by thick
septa of fibrous tissue that may contain smooth muscle (Fig. 14-11C,D). Cavernous hemangiomas show little contrast enhancement on imaging studies because their circulation is relatively stagnant. Other vascular lesions that affect the orbit include varices and arteriovenous malformations. Patients with orbital varices often show variable proptosis that depends on head position and is increased by a Valsalva maneuver. Histopathology shows a markedly dilated vein that may contain a thrombus (Fig. 14-12D). Intravascular papillary endothelial hyperplasia may develop in the thrombosed varix. Tumors previously diagnosed as hemangiopericytomas are now considered to be SFTs. Lymphangioma and capillary hemangioma are discussed in the “Pediatric Orbital Tumors” section below (Fig. 14-12).


Neurogenic Tumors

Neurogenic tumors of the orbit include schwannomas, neurofibromas, amputation neuromas, and malignant peripheral nerve sheath tumors.

Schwannoma or neurilemmoma (Fig. 14-13) is a well-circumscribed, encapsulated orbital tumor of adults composed of a neoplastic proliferation of Schwann cells, the perineural cells that form the myelin sheaths around axons in peripheral nerves. Many orbital schwannomas arise from sensory branches of the ophthalmic division of the trigeminal nerve and may be painful. Histopathology shows an encapsulated spindle cell neoplasm composed of cells with eosinophilic cytoplasm that have indistinct cellular borders and bland elongated oval nuclei. Two growth patterns are recognized. Tumors with the solid Antoni A pattern show bands of nuclear palisading and structures called Verocay bodies (Fig. 14-13C). The Antoni B pattern is marked by a loose myxomatous background. Schwannomas are immunoreactive with neural markers such as S100 protein and CD57 (Fig. 14-13D).






FIG. 14-11. Cavernous hemangioma (malformation), orbit. A. CT scan shows characteristically well-circumscribed oval mass within muscle cone. The differential diagnosis of a well-circumscribed orbital tumor also includes schwannoma, hemangiopericytoma, and SFT. B. After fixation, the well-circumscribed, encapsulated tumor appears bluish-purple in color and has a pebbly surface. C. The benign encapsulated tumor is composed of large blood-filled vascular channels separated by fibrous septa that are evident grossly. D. The large vascular channels constituting the benign vascular tumor are lined by a single layer of endothelial cells. The fibrous septa separating the vessels often contain smooth muscle. (D. H&E ×25.)

Isolated neurofibromas cause diffuse enlargement of the affected nerve and contain axons. They are pseudoencapsulated. Schwannomas and neurofibromas are often grouped together under the designation peripheral nerve sheath tumor. Schwannomas and isolated neurofibromas
are more prevalent in patients who have neurofibromatosis. Plexiform neurofibromas and diffuse neurofibromas are characteristic manifestations of neurofibromatosis type 1 (NF1). Malignant peripheral nerve sheath tumors are encountered rarely.






FIG. 14-12. Vascular lesions. A. Lymphangioma with secondary hemorrhage. Blood-filled chocolate cysts caused by secondary hemorrhage into lymphangioma are evident in this gross specimen. Many lymphangiomas contain blood. Lymphangiomas typically are unencapsulated and show an infiltrative growth pattern. B. Lymphangioma, orbit. Lymphoid channels constituting lymphangioma vary markedly in size and shape. They appear empty or contain serous fluid if intralesional hemorrhage has not occurred. Lymphoid foci in intervascular septa help to differentiate a lymphangioma with secondary hemorrhage from a cavernous hemangioma. Lymphangiomas typically are unencapsulated and have an infiltrative growth pattern. C. Capillary hemangioma. Mature capillary hemangioma is composed of a plexus of capillary caliber vessels. Early lesions often are composed predominantly of a solid sheet of endothelial cells. Vascular lumina develop and become progressively ectatic at the lesion matures. D. Thrombosed varix, orbit. A varix is a dilated or ectatic vein. An organized thrombus adheres to the wall of this orbital varix. (B. H&E ×10, C. H&E ×100, D. H&E ×5.)


Solitary Fibrous Tumor (SFT), Fibrous Histiocytoma, and Hemangiopericytoma

SFTs are fairly common spindle cell neoplasms that can affect the orbit (Fig. 14-14). Many orbital lesions that previously were diagnosed as FH and hemangiopericytoma prior to the ready availability of immunohistochemical diagnosis now are diagnosed as SFT. Essentially, there has been a change in terminology; prior clinical observations about FH and hemangiopericytoma of the orbit remain valid. All three of these lesions tend to be well-circumscribed orbital tumors.

SFT was initially diagnosed in the pleura. It often is composed of spindle cells that are arranged in a patternless pattern and are separated by thick bands of collagen. Diagnosis is confirmed by positive immunoreactivity for CD34 and STAT6 (Fig. 14-14E,F). Many tumors also stain for CD99 and BCL-2. SFTs have a characteristic gene fusion of the NAB2 and STAT6 genes.

Relatively rare orbital lesions, hemangiopericytomas originally were classified as vasculogenic soft tissue tumors that were thought to arise from pericytes in the walls of capillaries. Large sinusoidal vessels with a branching “staghorn” configuration are a classic histopathologic feature, and the reticulin stain shows that its constituent cells are totally enveloped by basement membrane. About 15% of patients with orbital lesions classified as hemangiopericytoma reported in 1982 by Croxatto and Font at the Armed Forces Institute of Pathology developed distant metastases. The histologic appearance of the tumor did not always predict
metastatic potential, as metastatic disease occasionally developed in patients with benign-appearing tumors. In recent years, authorities have stressed that SFT may show a branching staghorn hemangiopericytomatous vascular pattern (Fig. 14-14B,E). Some authorities have questioned whether hemangiopericytoma actually exists. The diagnosis is no longer included in the WHO classification of soft tissue tumors.






FIG. 14-13. Schwannoma (neurilemoma). A. Benign peripheral nerve sheath tumor appears grossly as piriform encapsulated mass. B. Cut surface has yellow-white translucent appearance with vascular foci. C. Antoni A portion (above) is composed of fascicles of bland spindle cells that show nuclear palisading and enclose tangles of fibrillary processes called Verocay bodies. A small focus of looser myxoid tumor (Antoni B pattern) is seen below. D. The tumor shows positive immunoreactivity for S100 protein. Schwannomas are well-circumscribed, encapsulated tumors that are associated with a peripheral nerve. (C. H&E ×100, D. IHC for S100 protein.)

Decades ago, FH was said to be the most common mesenchymal tumor of the orbit in adults. Currently, most of these tumors would be classified as SFT based on their immunoreactivity. Such lesions typically are well circumscribed but nonencapsulated, and their constituent spindle cells are said to be arranged in a characteristic whirling, pinwheel, or storiform pattern. Benign, locally aggressive, and rare malignant variants of FH were recognized, as is also the case with SFT. Although tumors classified as benign and locally aggressive cannot metastasize, total excision is recommended to prevent recurrence.

A variety of rare mesenchymal tumors of fibrous, fibroosseous, smooth muscle, adipose tissue or cartilaginous derivation occur in the orbit. Other extremely rare primary orbital tumors include endodermal sinus tumor, alveolar soft part sarcoma, granular cell tumor, paraganglioma, primary orbital carcinoid, primary orbital melanoma, retinal anlage tumor, neuroepithelioma, ectomesenchymal tumor, malignant rhabdoid tumor, and primitive neuroectodermal tumor.

Common fibro-osseous lesions of the orbital bones include fibrous dysplasia, juvenile psammomatoid ossifying fibroma, and ivory osteoma. Ivory osteoma is the most common bony lesion in adults. Fibrous dysplasia generally occurs in the first two decades and may spread across suture lines to involve multiple orbital bones. The affected bones have a “ground-glass” appearance in CT bone windows (Fig. 14-15A). Fibrous dysplasia is composed of irregular trabeculae of immature woven bone surrounded by

fibrous stroma (Fig. 14-15B-D). The bony trabeculae are not rimmed by osteoblasts and are often shaped like Chinese characters.






FIG. 14-14. Solitary fibrous tumor, orbit. A. SFT is encapsulated. B. Cellular tumor exhibits hemangiopericytomatous vascular pattern with vascular sinusoids. C. Spindle cells in this tumor are arranged in a “patternless pattern” and are separated by thick bands of collagen. D. Arrangement of tumor cells in this field resembles FH. E. Tumor cells are immunoreactive for CD34. A vascular sinusoid is present. F. Tumor cell nuclei stain for STAT6. (B. H&E ×50, C. H&E ×250, D. H&E ×250, E. IHC for CD34 ×100, F. IHC for STAT6 ×250.)






FIG. 14-15. Fibro-osseous lesions. A. Fibrous dysplasia. Lesion of nasal bones has “ground-glass” appearance on CT scan. Fibrous dysplasia may spread across suture lines to involve multiple orbital bones. B. Fibrous dysplasia. Fibrous stroma contains irregular trabeculae of immature woven bone, which are not rimmed by osteoclasts. Fibrous dysplasia represents an arrest in the maturation of bone. C. Polarization microscopy of fibrous dysplasia discloses an irregular interweaving pattern of collagenous matrix that resembles the fibers in woven cloth. D. In contrast, collagen fibers disclosed by polarization in mature lamellar bone form highly regular, parallel lamellae. E. Psammomatoid ossifying fibroma. The cellular stroma contains spindle cells and small spicules of bone called ossicles that can be confused with the psammoma bodies of meningioma. This benign lesion found in young individuals has an expansile growth pattern and behaves more aggressively than fibrous dysplasia. It usually does not cross suture lines and is restricted to a single orbital bone. (B. H&E ×25, C. H&E with crossed polarizers ×50, D. H&E with crossed polarizers ×50, E. H&E ×100.)

Juvenile ossifying fibroma is a more aggressive expansile lesion that usually is restricted to a single bone. Radiographically, it has a sclerotic margin and a less radiodense center. The cellular fibrous stroma of the psammomatoid variant of juvenile ossifying fibroma contains bony spicules that can be confused with psammoma bodies and lead to the misdiagnosis of meningioma (Fig. 14-15E).

The orbital bones occasionally are affected by a perplexing group of rare osseous lesions that contain giant cells including aneurysmal bone cyst, giant cell reparative granuloma, giant cell tumor, the brown tumor of hyperparathyroidism, and eosinophilic granuloma (see below). Osteogenic sarcoma and other soft tissue sarcomas can arise after radiotherapy for retinoblastoma.


THE LACRIMAL GLAND

The lacrimal gland is a minor salivary gland that is located in a bony fossa behind the superotemporal orbital rim (Fig. 14-16). Lacrimal gland tumors constitute only 10% to 15% of orbital lesions. Most lacrimal gland lesions encountered in nonreferral clinical practice are inflammatory or lymphoid tumors, which are at least five times more prevalent than primary epithelial tumors. Epithelial neoplasms of the lacrimal gland are quite rare, but they are important because about half are highly malignant tumors that are potentially lethal.

Granulomatous dacryoadenitis can cause bilateral lacrimal gland enlargement and a characteristic “s”-shaped lid fissure in patients with sarcoidosis (Fig. 14-6C). Keratoconjunctivitis sicca develops in patients with Sjögren syndrome when intense lymphocytic infiltration replaces
the parenchyma of the lacrimal gland. Damaged ducts and epimyoepithelial islands persist in the resultant benign lymphoepithelial lesion, and patients are at risk for lymphoma. Cystic dilation of lacrimal gland ducts (dacryops) may simulate a primary lacrimal gland tumor. Concretions or stones (dacryolithiasis) occasionally form in the ducts of the lacrimal gland.


Epithelial Tumors of the Lacrimal Gland

Compared to other salivary glands, the lacrimal gland gives rise to a relatively limited spectrum of primary epithelial neoplasms (Figs. 14-17, 14-18, 14-19). About one half of epithelial tumors of the lacrimal gland are pleomorphic adenomas or benign mixed tumors, and half are malignant. Lacrimal gland malignancies include adenoid cystic carcinomas (ACC), malignant mixed tumors derived from pleomorphic adenomas, and adenocarcinomas that have arisen de novo. Mucoepidermoid carcinoma is quite rare in the lacrimal gland and acinic cell (Fig. 14-19C), and Warthin tumors are almost nonexistent. The lacrimal gland gives rise to a greater proportion of malignant tumors than the parotid gland.

Epithelial tumors of the lacrimal gland typically arise in relatively young individuals whose average age at diagnosis is about forty. Several signs and symptoms are very important in the clinical evaluation of patients with lacrimal gland tumors. These include the duration of symptoms, the presence of pain, and the status of the orbital bones on imaging studies. A tumor is probably malignant if it is has been present for <6 months, the patient complains of pain, and there is radiographic evidence of bony erosion. Benign pleomorphic adenomas produce a regular, well-corticated fossa in the bone, not bone erosion.

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