Abstract
Metastatic melanoma to a pituitary oncocytoma is a very rare condition. A 76-year-old man was presented with progressive visual disturbance and falling down with initial loss of consciousness 2 days before admission. He had a subungual acral lentiginous melanoma (T3N1M0) with gangrenous change of left big toe, treated by amputation 15 months ago. Computed tomography and MR imaging demonstrated masses involving inguina, mediastinum and left renal hilum and dumb-bell shaped hyperdense mass, approximately 6.2 x 3.7 mm, that involved pituitary fossa and suprasellar region with adjacent bony destruction. He underwent surgical resection of the tumor. Microscopically, the tumor revealed an admixture of pituitary adenoma and invasive metastatic melanoma with fragments containing both populations in juxtaposition. The adenoma was negative for melanoma markers and pituitary hormone markers. The melanoma was positive for S-100 protein and BMB-45. Ultrastructure of the adenoma revealed abundant mitochondria and sparse secretory granules. The diagnosis was metastatic melanoma to a pituitary oncocytoma. The current literature on metastatic tumors to pituitary adenoma is reviewed.