Idiopathic retinal gliosis mimicking a choroidal melanoma.

A 37-year-old woman has followed for more than 10 years with an amelanotic peripheral intraocular tumor. This solitary lesion grew slowly and, because of the possibility of an amelanotic melanoma, the eye was enucleated. Histopathology revealed a localized "massive" retinal gliosis (MRG). Immunohistochemical staining for S-100 protein and glial fibrillary acidic protein (GFAP) were positive. Electron microscopy showed a highly fibrillar component and basement membrane formation in the extracellular space. Proliferating cells contained abundant fine filaments. These findings confirmed the glial origin of the proliferating cells. The previously undefined relationship of these localized forms of MRG with solitary astrocytomas is discussed.