Pigmented Epithelioid Angiomyolipoma of the Kidney

Extensive melanin pigment in an epithelioid angiomyolipoma, a potentially malignant and locally aggressive renal tumor, has been rarely reported. A 53-year-old, asymptomatic man with no significant past medical history underwent partial nephrectomy for a right kidney mass discovered on CT scan. Grossly, the mass was 4 cm, well-circumscribed, dark, brown-black. Microscopically, nests of large, clear-to-eosinophilic cells with mildly atypical, vesicular nuclei and prominent nucleoli were separated by striking vascular network. Abundant, brown-black, coarsely granular pigment was noted. The tumor stained with HMB-45 and MART-1 and was negative for broad spectrum cytokeratin, CK-7, CD-10, RCC antigen, EMA, vimentin, SMA, desmin, synaptophysin, chromogranin, and S 100. Fontana-Masson stain confirmed presence of melanin. Thick-walled vessels, spindle cells, and fat were absent. The patient had no family history of tuberous sclerosis. Close follow-up was recommended. It is important to differentiate this entity from melanoma, pigmented renal cell carcinoma, and pigmented paraganglioma.