Ring melanoma of the anterior chamber angle: a report of fourteen cases

Abstract

Purpose: Ring melanoma of the anterior chamber angle is a rare variant of uveal melanoma that manifests as circumferential, flat tumor growth predominantly confined to the trabecular meshwork and other anterior chamber angle structures. We report the clinical and histopathological features, management, and prognosis of ring melanoma of anterior chamber angle.

Methods: A retrospective review of clinical features, management, histopathologic features, and prognosis was performed. Of 8800 patients with uveal melanoma examined on the Oncology Service at Wills Eye Hospital over a 25-year period, only 14 patients (0.2%; 14 eyes) were classified clinically as ring melanoma of the anterior chamber angle. In no case was there appreciable involvement of the iris or ciliary body on clinical examination.

Results: The patients were followed elsewhere for a mean of 8 months before intraocular malignancy was suspected. Upon referral to the Oncology Service, the intraocular pressure was greater than 22 mm Hg in the affected eye in all patients (mean, 36 mm Hg; median, 35 mm Hg; range, 24 to 48 mm Hg), and all patients were using at least two glaucoma medications. The melanoma infiltrated the anterior chamber angle for a mean of 10 clock hours (range, 8 to 12 clock hours). Tumor management consisted of enucleation in 13 cases and plaque radiotherapy in one case. Histopathologic examination revealed epithelioid cell type melanoma in one case, mixed cell type in nine, and spindle cell type in four. Of the 13 patients who underwent enucleation, tumor cells were found within the Schlemm canal in all cases. Five cases displayed invasion of the intrascleral canals, and three showed episcleral invasion. With the exception of two recent cases, 12 patients were followed for a mean of 64 months (median, 47 months; range, 23 to 225 months). Distant metastasis to the liver was detected in three of 12 patients (25%) after a mean follow-up of 78 months (median, 70; range, 37 to 128 months).

Conclusions: Ring melanoma of the trabecular meshwork and angle structures is a rare variant of diffuse uveal melanoma. It often masquerades as unilateral glaucoma and can be difficult to recognize clinically unless careful comparative gonioscopy is performed. Despite the relatively small tumor volume, life prognosis is guarded with distant metastasis in 25% at mean 6 years follow-up.