angiomyolipoma

Angiomyolipoma is a benign renal tumor composed of blood vessels, smooth muscle, and adipose tissue. It is part of the family of perivascular epithelioid cell tumors (PEComas). Most AMLs occur sporadically in adults, but a subset is associated with tuberous sclerosis complex (TSC), in which lesions are more often multiple and bilateral.

Clinically, many AMLs are discovered incidentally during imaging for unrelated reasons. Larger lesions or those that rupture can cause flank pain or macroscopic hematuria. The risk of hemorrhage increases with tumor size and with pregnancy.

Radiologic diagnosis relies on imaging studies such as computed tomography or magnetic resonance imaging. The presence of macroscopic fat within a renal mass is highly suggestive of angiomyolipoma. In lesions with little or no fat (fat-poor AML), distinguishing from renal cell carcinoma can be challenging; histology confirms diagnosis. Pathology shows a triphasic admixture of thick-walled blood vessels, smooth muscle cells, and fat. Immunohistochemistry often shows positivity for melanocytic markers such as HMB-45 and Melan-A, along with smooth muscle actin.

Management depends on size, symptoms, and associations. Small, asymptomatic AMLs (<4 cm) are commonly observed with periodic imaging. Lesions at risk of bleeding or causing symptoms may be treated with selective arterial embolization or nephron-sparing surgery. In TSC-related AML, mammalian target of rapamycin (mTOR) inhibitors such as sirolimus or everolimus can shrink lesions. Pregnancy planning and monitoring are advised due to bleeding risk.

Prognosis is excellent, as AMLs are benign, but hemorrhage can be life-threatening if rupture occurs. Extrarenal angiomyolipomas are rare.