Perilimbal Conjunctival Schwannoma

Schwannomas are primary neurilemmal tumors composed of proliferatingSchwann cells. Schwannomas of ophthalmic interest more frequently involvethe orbit than the globe, but uveal schwannomas have been reported.¹ Rare among ocular schwannomas is the conjunctivalschwannoma. Seven have been described in the English-language literature,only 3 of which were located on the bulbar conjunctiva (Table 1).^2- 6

A 68-year-old white man was referred for excision of a pingueculum atthe 3-o'clock position of the left eye. The lesion of interest was 2.2 ×2 mm, well circumscribed, mobile, yellow, and perilimbal (Figure 1). A small pingueculum was also noted at the 9-o'clock position.The remainder of the examination results were unremarkable.

Surgical excision of the lesion at the 3-o'clock position was performedlargely to rule out squamous neoplasia. The lesion was easily excised withoutevidence of scleral extension.

Histologic sections and staining showed a well-circumscribed tumor composedof bland spindle cells with foci suggestive of nuclear palisading. There wereregions suggestive of Antoni A and B patterns. There was no connection withthe overlying mucosa. There was no atypia, necrosis, or mitotic activity (Figure 2A). Immunohistochemical studies demonstratedimmunoreactivity of the tumor cells for S100 protein (Figure 2B) and no reactivity for HMB-45. Reticulin stain showeddelicate fibers within the tumor.

Schwannomas are slow-growing, encapsulated, peripheral nerve sheathtumors that may be found in isolation or in association with von Recklinghausenneurofibromatosis.¹ Overall, schwannomastypically appear in the third to fifth decade of life and demonstrate no sexpredilection. Of the 7 previously reported conjunctival schwannomas, however,6 arose in women with ages ranging from 12 to 72 years^2- 6 (Table 1).

Schwannoma is not frequently included in the differential diagnosisof nonpigmented conjunctival masses, which consists of pingueculum, nevus,foreign body, neurofibroma, leiomyoma, fibrous histiocytoma, dermoid, squamousand sebaceous cell carcinomas, and amelanotic malignant melanoma. Schwannomasare composed of a pure proliferation of Schwann cells. Two distinct, interminglinghistologic patterns are seen: an Antoni A pattern of sheets of palisadingspindle cells with spindle-shaped nuclei forming Verocay bodies, and an AntoniB pattern of haphazardly arranged elongated cells in a myxoid stroma.¹ Light-microscopic features of schwannoma are usuallycharacteristic, but immunohistochemistry may be required in some cases.

The tumor presented herein was a bland, well-circumscribed spindle celltumor with immunohistochemical profile favoring the diagnosis of schwannoma.Antibodies directed against the S100 protein identify melanocytes and neuralcrest–derived cells, thereby excluding fibrohistiocytic and smooth-muscletumors. HMB-45 antibodies identify cells of melanocytic origin and are a sensitivemarker for melanoma and nevi. In addition, the reticulin stain showed abundantfibers that are prominent in most schwannomas.¹

Fibrous histiocytoma and leiomyoma are often confused with schwannomasbecause of their spindle cell morphologic characteristics, but can be distinguishedby their lack of S100 expression.¹ Neurofibromasare S100-positive Schwann cell tumors, but include fibroblasts and perineuralcells, and nuclear palisading is less common. The circumscription, bland cytologicfeatures, and absence of atypia, necrosis, or mitotic activity essentiallyrule out a malignant tumor.

In summary, we report a rare case of perilimbal conjunctival schwannoma.We suggest this diagnosis be included in the differential diagnosis of amelanoticconjunctival lesions.

Corresponding author: Aaron M. Fay, MD, Massachusetts Eye and EarInfirmary, 243 Charles St, Boston, MA 02114 (e-mail: Aaron_Fay@meei.harvard.edu)