Angiomyolipoma of kidney.

Angiomyolipoma of the kidney is a clonal neoplasm, apparently part of a family of neoplasms derived from perivascular epithelioid cells. Early angiomyolipomas are small nodules composed of HMB-45-reactive spindle cells in the renal capsule, cortex, or medulla. Most angiomyolipomas are asymptomatic, and they are more common than previously appreciated, approaching 13 per 10,000 adults. They are much more prevalent in patients with tuberous sclerosis, where they often are accompanied by cysts and occasionally by renal cell carcinoma. That they are rarely diagnosed before puberty in patients without tuberous sclerosis, that large ones are more common in women than men, and that they occasionally grow rapidly during pregnancy suggest that hormones may play a role in stimulating the growth of angiomyolipoma. Pathologists should recognize that the presence of multiple angiomyolipomas is, at the least, presumptive evidence for the diagnosis of tuberous sclerosis and include this in their reports. Typical angiomyolipomas are benign but may have alarming properties: nuclear pleomorphism and mitotic activity, extension into the vena cava (21 cases), and spread to regional lymph nodes (39 cases), without malignant progression. The most common serious complication of renal angiomyolipoma is hemorrhage. Epithelioid angiomyolipoma is a recently recognized variant with malignant potential. Angiomyolipoma and lymphangiomyoma are closely related, and tumors with features of both have occurred. Angiomyolipomas have occurred in other organs in association with renal angiomyolipoma.