Schwannoma (neurilemoma) is a benign, encapsulated tumor that arises from the Schwann cells that ensheath peripheral nerves. It can arise primarily in the orbit or extend into the orbit from adjacent peripheral nerves (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18). It accounts for about 1% of all orbital masses (1,2,3,4). In the authors’ series of 1,264 consecutive space-occupying orbital lesions, the 14 schwannomas accounted for 61% of the 23 peripheral nerve tumors and for 1% of all lesions. It was diagnosed at a median age of 37 years with a range from 10 to 84 years.

Orbital schwannoma usually produces proptosis and displacement of the globe with signs and symptoms similar to those described for orbital cavernous hemangioma. Even though it is a tumor of peripheral nerve sheath origin, it does not usually cause pain. In contrast with neurofibroma, solitary orbital schwannoma is not usually associated with neurofibromatosis.

Imaging studies disclose a solid ovoid to elongated mass usually outside the muscle cone along the course of the supraorbital or supratrochlear nerve and occasionally along the infraorbital nerve. Magnetic resonance imaging (MRI) reveals an enhancing mass with signals that vary depending on whether the tumor is solid or cystic. It shows very low signal on T1-weighted images and homogeneous postcontrast enhancement (10).

Histopathologically, schwannoma is a benign proliferation of Schwann cells that can show several variations in one tumor. Some areas are characterized by ribbons or fascicles of spindle cells (Antoni A pattern) and other areas have ovoid clear cells (Antoni B pattern). Large cystoid spaces are sometimes present and can even occupy most of the tumor, suggesting a cystic, rather than a solid lesion.

Ancient schwannoma is a variant of schwannoma that can be confused with a malignant mesenchymal tumor because of increased cellular, nuclear pleomorphism, and hyperchromatism. The variant often shows cyst formation, calcification, hemorrhage, and hyalinization (5).

Although there are no immunohistochemical stains that are specific for Schwann cells, immunohistochemistry can be used to exclude the diagnosis of other spindle cell tumors, like melanoma, leiomyoma, and rhabdomyosarcoma, thus lending support to the diagnosis of schwannoma. Electron microscopy can be used to demonstrate the cytoplasmic wide-spacing collagen that characterizes Schwann cells (1,5).

The management of orbital schwannoma is surgical excision. Axial and coronal MRI and/or computed tomography (CT) are essential in determining the best approach to surgical excision. An incisional biopsy should generally not be done for this circumscribed orbital tumor. If the tumor is not completely excised at a fairly early stage, it can show progressive growth, attain a large size, and be more difficult to excise.

Orbital schwannoma most typically occurs in the superior extraconal portion of the orbit and apparently arises from the sheath of the supraorbital nerve. When it is in that location, it is best approached by a superolateral orbitotomy. Most can be successfully removed by a soft tissue approach; osteotomy is only occasionally necessary. A clinicopathologic correlation is presented.

Orbital schwannoma is a benign, slowly growing tumor that can cause compression of the optic nerve and visual impairment. Once the tumor is removed, the optic disc swelling can resolve and the visual acuity can return to normal. However, the choroidal folds tend to remain.

Because orbital schwannoma is a well-circumscribed, encapsulated tumor, it can sometimes be removed intact by way of lateral orbitotomy despite its large size and posterior location. Illustrated is a clinicopathologic correlation of a large schwannoma in a 33-year-old man who declined a recommended neurosurgical approach and sought another opinion to see if it could be removed without a craniotomy. It was removed intact by way of a superolateral orbitotomy despite the fact that it protruded posteriorly through the superior orbital fissure.

Shields JA, Kapustiak J, Arbizo V, et al. Orbital neurilemoma with extension through the superior orbital fissure. Arch Ophthalmol 1986;104:871-873.

Neurofibroma is a benign peripheral nerve tumor that can affect the orbit (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28). In the authors’ series of 1,264 consecutive space-occupying orbital lesions, the 6 neurofibromas accounted for 26% of the 23 peripheral nerve lesions and for, 1% of all lesions. It can be divided into localized, diffuse, and plexiform types (17). Among our 6 cases, there were 4 plexiform and 2 solitary neurofibromas. The localized type is clinically and radiographically similar to schwannoma and is associated with neurofibromatosis type 1 in about 10% of cases (25). The diffuse type has a variable association with neurofibromatosis and the plexiform type is almost always seen in association with neurofibromatosis.

Localized neurofibroma produces clinical symptoms and signs similar to schwannoma and other circumscribed orbital tumors and can manifest as proptosis, globe displacement, diplopia, and optic nerve compression. It is usually diagnosed in middle-aged or adult patients and, as mentioned, does not occur in patients with neurofibromatosis type 1. Localized neurofibroma can sometimes occur as multiple orbital tumors in patients without clear evidence of neurofibromatosis. In such cases, pain may be a prominent symptom (27).

Diffuse and plexiform neurofibromas are very similar clinically and radiographically, but are classified separately because of subtle histopathologic differences (5). They generally become clinically apparent in the first decade of life and show gradual progression, often with involvement of other periocular and ocular tissues, including the uveal tract. The diffuse, poorly defined mass can cause the classic S-shaped curve to the upper eyelid owing to subcutaneous involvement by the tumor. The plexiform form can be very extensive with massive involvement of the orbit, eyelids, and intraocular structures. In addition, patients with neurofibromatosis can have congenital defects in the sphenoid bone that can produce a characteristic pulsating proptosis similar to that seen with encephalocele.

With orbital computed tomography and magnetic resonance imaging, localized neurofibroma appears as a circumscribed mass that is indistinguishable from schwannoma, described previously (6). Plexiform and diffuse neurofibromas show an irregular, ill-defined mass, often with extensive periorbital involvement, as mentioned.

Localized orbital neurofibroma is circumscribed but lacks a true capsule. The classical case shows interlacing bundles of elongated spindle cells with variable quantities of mucoid material. Diffuse and plexiform neurofibromas are composed of a complex intertwining of bundles of enlarged nerves with proliferation of Schwann cells and endoneural fibroblasts in a mucoid matrix. A distinct perineural sheath defines the individual tumor cores. The histopathologic findings of neurofibroma are discussed in more detail elsewhere (5).

A patient with suspected localized orbital neurofibroma should be evaluated and managed as described for other localized orbital tumors. Clinical findings and imaging studies should be done and complete surgical excision should be considered for symptomatic lesions.

The diffuse, unresectable plexiform type should be managed more conservatively. However, surgical intervention is often necessary because of bothersome symptoms, threatened vision, or an unacceptable cosmetic appearance. In such instances, debulking surgery is often done, because complete surgical removal may not be possible. Depending on the extent of the disease, a combined approach with neurosurgeons and otolaryngologists may be prudent (19,24).