Angiomyolipoma (AML): Benign Kidney Tumor – Symptoms, Diagnosis, Treatment

Angiomyolipoma (AML) is a benign mesenchymal tumor composed of blood vessels, smooth muscle, and adipose tissue.

Epidemiology

• Most common in kidney (renal AML); also liver, spleen, colon, lung.
• Strong association with tuberous sclerosis complex (TSC) (bilateral, multiple, younger onset).
• Sporadic: usually solitary, women > men, 40s–60s.

Clinical Presentation

• Asymptomatic (majority): Incidental on imaging for other reasons.
• Symptomatic (large >4 cm): Flank/abdominal pain, palpable mass, hematuria.
• Life-threatening: Spontaneous retroperitoneal hemorrhage (Wunderlich syndrome) – risk ↑ with size >4 cm, pregnancy, TSC.

Diagnosis

• Ultrasound: Hyperechoic (fat), may shadow.
• CT (gold standard): Fat density (<-20 HU) diagnostic. Enhancing soft tissue components = vessels/muscle.
• MRI: Fat signal on T1; chemical shift artifact.
• Biopsy: Rarely needed if imaging classic; risk of bleeding.

Management

• Surveillance: <4 cm, asymptomatic – periodic imaging.
• Embolization (first-line for >4 cm / symptomatic): Selective angiographic embolization – preserves renal parenchyma.
• Surgery: Partial nephrectomy (preferred), radical if necessary. For failed embolization, suspicion of malignancy, non-embolizable anatomy.
• mTOR inhibitors (sirolimus): For TSC-associated AMLs (shrinks tumors).

Prognosis

Excellent for sporadic AML. TSC patients require lifelong multidisciplinary care. Malignant transformation (epithelioid AML) is rare.