Schwannomas are benign, encapsulated, primary neurilemmal tumors composed of proliferating Schwann cells. The most common location for schwannomas is the head and neck region followed by the flexor surfaces of the limbs and the trunk. Schwannomas can occur in isolation or in association with neurofibromatosis type I or type II. In the ophthalmic region, schwannomas are most commonly seen in the orbit. Other reported locations include choroid, caruncle, sclera, and conjunctiva. Epibulbar schwannomas are very rare with less than ten cases being described in the literature. We report a case of a 12-year-old boy who presented to us with a slow-growing painless subconjunctival mass in the left eye. There was no intraocular extension of the mass. Intra-operatively, the mass could be clearly delineated and was excised off the underlying sclera. Histopathological examination of the mass showed typical features of schwannoma. There were no systemic features suggestive of neurofibromatosis and no subsequent recurrence of the lesion was noted. In this communication, we report this uncommon entity and review the typical clinical features of an epibulbar schwannoma. Although rare, an epibulbar schwannoma should be considered in the differential diagnosis of an amelanotic, painless subconjunctival nodular mass. Excision of the lesion is curative, and recurrence is uncommon.
A healthy 12-year-old boy presented with complaints of a slow growing painless conjunctival mass of 3 years’ duration in the left eye. On examination, his uncorrected visual acuity in both eyes was 20/20 N6. There was a subconjunctival, nontender, well-defined, multi-lobed, immobile, firm mass with scleral fixity at 5’O-clock position of the left eye. The mass was prominent on dextroelevation [Fig. 1a and b]. There was no restriction of motility and the anterior and posterior segments in both eyes were within normal limits. Ultrasound biomicroscopy of the lesion showed uniform internal low reflectivity. Computed tomography of the orbits confirmed a well-defined mass in close relation to the globe with homogenous consistency and the extraocular muscles were seen distinctly separate from the mass. Differential diagnosis based on clinical examination included atypical nodular scleritis, scleral nodule, hemangioma, parasitic cyst, or a myxoma. The patient subsequently underwent excision of the mass. Intraoperatively, the mass was found to be entirely subconjunctival and adherent to the sclera [Fig. 1c]. However, it could be separated from the underlying sclera and excised in-toto [Fig. 1d]. Double freeze-thaw cryotherapy was done at its location over the sclera, and the conjunctiva was closed with 8-0 vicryl suture. The histopathological examination of the hematoxylin-eosin stained slides showed tumor consisting of spindle cells arranged in whorls and twisted conFigureuration, which were the Antoni-A areas as well as the irregularly arranged, paucicellular Antoni-B areas [Fig. 2a]. The cells were elongated with thin cytoplasmic processes, and the nuclei were arranged in parallel lines which assumed a typical “picket fence” pattern; features that were typical of a benign schwannoma. The tumor cells also stained strongly positive for S100, a highly sensitive marker for melanocytes and neural crest-derived cells; thus confirming the diagnosis of epibulbar schwannoma [Fig. 2b]. The patient did not have features of neurofibromatosis. At a follow-up of 26 months, there was no recurrence of the lesion. He has been advised annual follow-up and is being monitored for clinical signs suggestive of neurofibromatosis.
Conjunctival/epibulbar schwannoma is an uncommon tumor. In a retrospective, non-interventional case series of 1643 consecutive patients with conjunctival tumors by Shields et al., there were no cases of conjunctival/epibulbar schwannoma. In a large review of 2455 conjunctival tumors by Grossniklaus et al., a single case of conjunctival schwannoma was reported in a 61-year-old male.
Le Marc’hadour et al. described the electron microscopic features of conjunctival schwannoma in a 37-year-old male patient. The tumor almost entirely consisted of Schwann cells that also enclosed myelinated fibers and were coated by a basal lamina. In between cell bodies, there were numerous Schwann cell processes that were seen admixed with non-myelinated fibers. Also, neuritic processes were seen and were encircled by Schwann cell plasma membrane, leading to the formation of mesaxons.
Conjunctival/epibulbar schwannomas have an indolent clinical course. They usually present as a slow growing painless nodule on the conjunctiva/epibulbar surface. Based on published literature, the age at presentation varies from 10 to 72 years ,26, [Table 1]. There is no obvious sex predilection with 6 of the 10 cases (60%) reported being female. As elucidated by Demirci et al., since the bulbar conjunctiva is the most common site of this tumor, “epibulbar schwannoma” is probably the most apt description. Nils Antoni, a Swedish neurologist, described two distinct patterns of cellular architecture in the peripheral nerve sheath tumors. The first was what appeared to be a “fibrillary, intensely polar, elongated appearing tissue type” which was called “tissue type A.” These highly cellular regions were eventually referred to as Antoni-A regions. He also described seemingly distinct, loose microcystic tissue adjacent to the Antoni-A regions, and these came to be known as Antoni-B regions. These tumors eventually were referred as schwannomas. The conjunctiva receives its sensory nerve supply from the nasociliary nerve; in addition there are autonomic nerves that are subconjunctival in location. It has been hypothesized that such epibulbar schwannomas possibly arise from any of these nerves.
The treatment of epibulbar schwannomas is complete excision. While excising, one must be careful to excise it in-toto and prevent damage to the underlying sclera. Scleral involvement from the overlying lesion has been noted in two cases. Additional double freeze cryotherapy to the base, namely the underlying sclera, in addition to our case; was done in only one of the reported cases. However, it is unlikely that cryotherapy has any role in preventing recurrence, given the benign pathology of the tumor. Furthermore, no malignant transformation was noted in any of the other cases. Epibulbar or conjunctival schwannoma can be best described as a common tumor at an uncommon site. It has a benign course with excision being curative in most cases.
A systematic Medline search was performed on PubMed using the key words: Schwannoma, neurilemmoma, conjunctiva, conjunctival, and epibulbar. There was no restriction on the date of publication. While this review relied on English articles, non-English language articles that had abstracts translated into English were also reviewed.
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