Small choroidal melanoma with massive extraocular extension: invasion through posterior scleral emissary channels.

Massive orbital extension arising from a small posterior pole uveal melanoma is rare. A 75-year-old male followed for an asymptomatic choroidal nevus developed a two and a half month history of mild decrease in visual acuity. Upon clinical examination minimal enlargement of the tumor with surrounding serous retinal detachment was observed. Pre-operative magnetic resonance imaging disclosed massive extrascleral extension. Histopathology revealed that the tumor was composed of spindle B malignant melanoma cells. Multiple serial sections of the entire tumor area failed to demonstrate permeation through scleral lamellae. Instead, peripapillary perivascular short posterior ciliary vessel invasion was observed. This route of dissemination may explain the rapid growth and clinically undocumented behavior of small malignant melanomas at this location.