Genitourinary Radiology > Kidneys > Masses > Solid > Angiomyolipoma


Angiomyolipomas are hamartomas containing fat, smooth muscle, and blood vessels. Most are asymptomatic, but may hemorrhage if large. Larger symptomatic lesions (> 4 cm) can be resected or embolized. Eighty percent of patients with tuberous sclerosis have AML, usually multiple lesions bilaterally.

The most distinctive feature of angiomyolipomas is fat, appearing as a hypodense (CT), hyperechoic (US), and hyperintense (T1 weighted MRI) mass. The presence of fat is almost pathognomic for AML -- the other unlikely possibilities are RCC engulfing adjacent renal sinus fat and oncocytoma. Prominent blood vessels lead to strong enhancement (CT or MRI) and high signal intensity on T2 weighted images. If muscle is the predominate component of the mass, it will appear with similar density or intensity as renal cell carcinoma. Calcifications are not a common finding of angiomyolipomas and would lead towards a diagnosis of renal cell carcinoma.

Contrast enhanced CT scan through the kidneys shows a large fatty mass (similar attenuation to the surrounding retroperitoneal fat (R) emanating from the anterior aspect of the right mid kidney (arrows). Fatty mass arising from the kidney is pathognomic of angiomyolipoma (AML).

Non enhanced and contrast enhanced CT scan through the kidneys shows bilateral small low density lesions (arrows). Most of the lesions are too small to accurate measure their density. However, larger lesions did demonstrate fat consistent with bilateral angiomyolipomas in a patient with tuberous sclerosis.

Gray scale ultrasound in patient with multiple small bilateral echogenic foci (arrows). Several things are echogenic on ultrasound, besides calcifications, fat is also echogenic. Calcifications often shadow (no information deep to the calfication because all sound is reflected at the calcifcations interface). These lesions, however, did not call dense acoustic shadowing and they represented small angiomyolipomas in a patient with tuberous sclerosis.

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