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Editor,—Melanocytic lesions of the episclera include Axenfeld nerve loop, episcleral melanocytosis, ochronosis, conjunctival naevus, cellular blue naevus, melanocytoma, conjunctival melanoma with deep extension, extraocular extension of uveal melanoma, or metastatic melanoma.1-5 The occurrence of an episcleral melanoma without conjunctival, uveal, or skin involvement is extremely rare. We report an unusual case of malignant melanoma occurring as an isolated tumour on the episcleral surface.
A 36 year old healthy man developed a pigmented epibulbar lesion in the left eye over a 1 year period. There was no history of ocular trauma, cutaneous melanoma, or dysplastic naevus syndrome. Ocular examination revealed visual acuities of 6/6 in both eyes. In the left eye, there was an episcleral pigmented mass located 2 mm from the limbus at the 10 o’clock position, measuring 4.0 × 3.5 mm in base (Fig 1). The conjunctiva was freely mobile over the lesion. Anterior segment examination was otherwise normal with no sign of conjunctival naevus, primary acquired melanosis, or malignant melanoma. There was no evidence of an intraocular melanoma by funduscopy. On transillumination, blockage of light transmission by the epibulbar lesion was noted. The differential diagnosis included an episcleral cellular blue naevus, melanocytoma, melanoma, or foreign body.
The epibulbar lesion was removed via “no touch” partial lamellar scleroconjunctivectomy approach with wide margins and supplemental cryotherapy to the surrounding conjunctiva. After surgery, there was no transillumination light blockage. Pathological examination disclosed a deep subconjunctival lesion comprised of epithelioid melanocytes with prominent nucleoli, consistent with malignant melanoma (Fig 2). Mitoses were not observed. There was no evidence of primary acquired melanosis. Similarly, an emissarial scleral canal at the base of the mass was tumour free. Subsequent systemic evaluation revealed no sign of primary melanoma elsewhere. The patient has been followed for 1 year with no evidence of recurrence or metastasis.
Episcleral melanoma may be impossible to clinically differentiate from cellular blue naevus or melanocytoma. A careful conjunctival and funduscopic examination is necessary to rule out extraocular extension from an uveal melanoma or contiguous spread from a conjunctival melanoma. In order to thoroughly rule out metastatic melanoma, a systemic evaluation should be performed. Melanoma originates mostly in the skin (86%), followed by the eye (11%), vulva (1%), soft tissues (<1%), rectum (<1%), and vagina (<1%).6 In our patient, there was no evidence of primary melanoma elsewhere, although we realise that metastatic melanoma can occur in the body without detection of a primary site. In a series of 10 metastatic tumours to the conjunctiva, there were two cases of cutaneous metastatic melanoma both of which also had uveal metastasis.5 However, our patient had no evidence of an intraocular tumour.
The origin of the episcleral melanoma remains obscure, although most probably it arises from melanocytes deep in the subconjunctival tissues. Malignant melanoma should be considered in the differential diagnosis of an episcleral pigmented lesion.
Supported by the Paul Kayser International Award of Merit in Retina Research, Houston, TX (J Shields) and Eye Tumor Research Foundation, Philadelphia, PA, USA.