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Arch Ophthalmol. 2004;122:388-389.

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

View this table: [in this window] [in a new window] Reported Cases of Conjunctival Schwannoma

Report of a Case
A 68-year-old white man was referred for excision of a pingueculum at the 3-o'clock position of the left eye. The lesion of interest was 2.2 x 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.

View larger version (68K): [in this window] [in a new window] Figure 1. Left eye showing a 2.2 x 2-mm elevated, well-circumscribed, mobile, yellow, perilimbal conjunctival lesion at the 3-o'clock position.

Surgical excision of the lesion at the 3-o'clock position was performed largely to rule out squamous neoplasia. The lesion was easily excised without evidence of scleral extension.

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

View larger version (98K): [in this window] [in a new window] Figure 2. Histologic features of the excised tumor. A, Periodic acid–Schiff preparation at approximately x40 magnification showing spindle cell morphologic characteristics with areas suggestive of Antoni A and B patterns. B, Immunohistochemical staining showing tumor cells positive for S100 protein at approximately x400 magnification. The positive reaction is seen as a rust color.

Comment
Schwannomas are slow-growing, encapsulated, peripheral nerve sheath tumors that may be found in isolation or in association with von Recklinghausen neurofibromatosis.¹ Overall, schwannomas typically appear in the third to fifth decade of life and demonstrate no sex predilection. 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 diagnosis of nonpigmented conjunctival masses, which consists of pingueculum, nevus, foreign body, neurofibroma, leiomyoma, fibrous histiocytoma, dermoid, squamous and sebaceous cell carcinomas, and amelanotic malignant melanoma. Schwannomas are composed of a pure proliferation of Schwann cells. Two distinct, intermingling histologic patterns are seen: an Antoni A pattern of sheets of palisading spindle cells with spindle-shaped nuclei forming Verocay bodies, and an Antoni B pattern of haphazardly arranged elongated cells in a myxoid stroma.¹ Light-microscopic features of schwannoma are usually characteristic, but immunohistochemistry may be required in some cases.

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

Fibrous histiocytoma and leiomyoma are often confused with schwannomas because of their spindle cell morphologic characteristics, but can be distinguished by their lack of S100 expression.¹ Neurofibromas are S100-positive Schwann cell tumors, but include fibroblasts and perineural cells, and nuclear palisading is less common. The circumscription, bland cytologic features, and absence of atypia, necrosis, or mitotic activity essentially rule 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 amelanotic conjunctival lesions.

AUTHOR INFORMATION

Christopher M. Andreoli, MD; Mark Hatton, MD
Boston, Mass

Joseph P. Semple, MD
Middletown, Conn

Sarkis H. Soukiasian, MD
Burlington, Mass

Aaron M. Fay, MD
Boston

Corresponding author: Aaron M. Fay, MD, Massachusetts Eye and Ear Infirmary, 243 Charles St, Boston, MA 02114 (e-mail: Aaron_Fay{at}meei.harvard.edu).

REFERENCES
1. Spencer WH. Ophthalmic Pathology: An Atlas and Textbook. 4th ed. Philadelphia, Pa: WB Saunders Co; 1995;1653-1689, 2645-2650. 2. Dabezies OH Jr, Penner R. Neurofibroma or neurilemmomoma of the bulbar conjunctiva. Arch Ophthalmol. 1961;66:73-75. 3. Vincent NJ, Cleasby GW. Schwannoma of the bulbar conjunctiva. Arch Ophthalmol. 1968;80:641-642. PUBMED 4. Grossniklaus HE, Green WR, Lukenbach M, Chen CC. Conjunctival lesions in the adults: a clinical and histopathologic review. Cornea. 1987;6:78-116. PUBMED 5. Le Marc'hadour F, Romanet JP, Fdili A, Peoc'h M, Pinel N. Schwannoma of the bulbar conjunctiva. Arch Ophthalmol. 1996;114:1258-1260. ABSTRACT 6. Charles NC, Fox DM, Avendano JA, Marroquin LS, Appleman W. Conjunctival neurilemoma: report of 3 cases. Arch Ophthalmol. 1997;115:547-549. ABSTRACT

SECTION EDITOR: W. RICHARD GREEN, MD