Spectrum of Renal Angiomyolipoma with Radiologic-Pathologic Correlation.

Angiomyolipoma (AML) is a benign tumor comprised of a mixture of vessels ("angio"), smooth muscle ("myo"), and adipose tissue ("lipo"). It belongs to a group of unusual mesenchymal tumors with myogenic and melanocytic differentiation known as perivascular epithelioid cell tumors. AMLs are commonly sporadic tumors but may be associated with tuberous sclerosis complex (TSC) and/or lymphangioleiomyomatosis (LAM). The imaging appearance of AMLs strongly correlates with the pathologic findings. Fat is detectable in the vast majority of AMLs, and these tumors are referred to as classic AMLs. Fat-poor AMLs are smooth muscle-predominant tumors. The smooth muscle content drives the imaging findings, which include increased attenuation on non-contrast-enhanced CT images, low T2 signal intensity, and avid enhancement. Rare histologic variants of AMLs include epithelioid AML (EAML) and AML with epithelial cysts. Most AMLs exhibit benign clinical behavior. The most important clinical complication of AML is tumor hemorrhage, which may lead to retroperitoneal hemorrhage and shock. Hemorrhage most commonly occurs in large tumors or tumors with aneurysms equal to or larger than 5 mm. Benign AMLs may also invade the renal vein and inferior vena cava. EAMLs may behave aggressively with local recurrence and metastatic spread. Treatment options for AML vary and may include observation for small classic AMLs; embolization, ablation, and/or surgical resection of large or potentially aggressive lesions; or systemic therapy in cases associated with TSC or LAM. RSNA, 2025 Supplemental material is available for this article.