Primary orbital melanoma associated with orbital melanocytosis.

We report a case of primary orbital melanoma in a 17-year-old girl. The patient presented with painless proptosis during the first trimester of pregnancy. Computed tomography demonstrated a well-circumscribed mass located infra-temporally in the right orbit. The tumor was bluish-black, grossly encapsulated, and associated with orbital blue nevi. Histologic examination of the mass revealed a pigmented spindle-cell neoplasm. On electron microscopy, the presence of premelanosomes and the absence of basal lamina supported the diagnosis of melanoma. Malignant transformation of a preexisting nevus is postulated since perineural foci of benign dendritic melanocytes were seen within the melanoma. There has been no recurrence or metastasis in a 2-year follow-up. Of 30 primary orbital melanomas reviewed, 12 (40%) were associated with periorbital pigmentary disorders, such as oculodermal melanocytosis, blue nevus, and ocular melanocytosis. Our case is unique since the pigmentary lesions were limited to the orbital tissues.