Angiomyolipoma with hemorrhage
Axial and coronal noncontrasted computed tomography (CT) images demonstrate a large left fat-containing mass arising from the left kidney. High-density fluid is noted along the periphery of the fat-containing mass, most prominent along the medial border. Comparison with prior examinations showed the high-density fluid was new.
Angiomyolipoma (AML) is a benign neoplasm composed of fat, smooth muscle, and vascular elements. Approximately 80% of angiomyolipomas occur sporadically, while 20% are associated with tuberous sclerosis. The majority of AMLs are detected incidentally by imaging and occur 4 times more commonly in females.
AMLs are benign, well-defined tumors, which arise from the renal parenchyma. They are unencapsulated, which permits extension into the perirenal fat. AMLs are commonly identified on CT where they are most easily identified by macroscopic fat density (approximately <20 HU) within the lesion. Small AMLs may be difficult to diagnose secondary to volume averaging which obscure macroscopic fat. In addition, a small percentage of AMLs demonstrate little to no fat, which may also make diagnosis difficult.
Ultrasound evaluation of AML should demonstrate a cortically-based hyperchoic lesion with posterior acoustic shadowing. As with CT, lipid-poor and small AMLs are more difficult to diagnose. MRI is an excellent tool for diagnosing AMLs, as fat-saturation images will demonstrate signal dropout within the lesion and out-of-phase images will demonstrate an “India ink” artifact surrounding the AML.
The majority of AMLs are asymptomatic and of no clinical significance. However, larger AMLs (>4cm) are prone to hemorrhage, which in some cases may be life threatening. The propensity for hemorrhage is secondary to poorly organized vascular tissue, which may result in aneursym formation. Treatment of excessive or recurrent hemorrhage consists of arterial embolization.
- Yamakado K, Tanaka N, Nakafawa T, et al. Renal angiomyolipoma: Relationships between tumor size, aneursym formation and rupture. Radiology. 2002;225:78-82.
- Eble JN. Angiomyolipoma of kidney. Semin Diagn Pathol. 1998;15:21-40.
- Umeoka S, Koyama T, Miki Y, et. al. Pictorial review of tuberous sclerosis in various organs. Radiographics. 2008;28:e32.