Angiomyolipomas

Angiomyolipomas are benign neoplasms composed of blood vessels, smooth muscle cells, and adipose tissue, arising most commonly in the kidney. They belong to the PEComa family (perivascular epithelioid cell tumors). They can occur sporadically or in association with tuberous sclerosis complex (TSC) and lymphangioleiomyomatosis (LAM); extrarenal angiomyolipomas may be seen in the liver or other sites.

Most renal angiomyolipomas are incidental findings in adults and are more common in women. They may be asymptomatic, but larger lesions can cause flank pain, hematuria, or a palpable mass. Spontaneous retroperitoneal hemorrhage is a serious complication, particularly with larger tumors or aneurysm formation; pregnancy may increase bleeding risk.

On imaging, AMLs characteristically show fat within the lesion on CT or MRI; however some lesions are fat-poor and can mimic other renal tumors such as renal cell carcinoma or liposarcoma. Angiomyolipomas are typically HMB-45 positive on immunohistochemistry and express melanocytic and smooth muscle markers. Pathology shows a triphasic composition of thick-walled blood vessels, smooth muscle, and adipose tissue.

Management ranges from observation to intervention. Small, asymptomatic AMLs usually are monitored with interval imaging. Prophylactic treatment is considered for tumors about 3–4 cm or those with aneurysmal dilation, symptomatic lesions, or in patients with TSC/LAM. Options include selective arterial embolization, nephron-sparing surgery, or ablation. mTOR inhibitors such as everolimus or sirolimus are used for TSC- or LAM-associated AMLs to shrink lesions.

Prognosis is generally favorable; AMLs are benign with low malignant potential. Hemorrhage risk guides management, and with appropriate treatment most patients have good outcomes. Regular follow-up imaging is tailored to size, symptoms, and associated conditions.