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Angiomyolipomas (AML) are hamartomatous lesions comprised of fat cells, smooth muscle cells, and blood vessels in various proportions. AMLs, while neoplastic lesions, are benign and do not metastasize. They appear in 2 distinct forms: as part of the tuberous sclerosis complex or sporadically. About 80% of AMLs occur sporadically in patients without tuberous sclerosis, and these are more common in middle-aged females. AMLs in patients with tuberous sclerosis complex more commonly present at an earlier age, larger size, greater number, and with hemorrhage more often than sporadic cases.

With modern imaging techniques, the majority of AMLs are incidentally discovered. However, common presenting symptoms include flank pain, hemorrhage, and hematuria. Retroperitoneal hemorrhage associated with spontaneous rupture is a life-threatening presentation occurring in up to 15% of patients.

AMLs can usually be diagnosed based upon characteristic imaging findings. On ultrasound, AMLs are markedly hyperechoic lesions. On CT, macroscopic fat is suggestive of an AML; however, some lesions contain minimal fat and may therefore be difficult to differentiate from renal malignancies and some renal cell carcinomas (RCC) have been reported to contain macroscopic fat. MRI is superior to CT in differentiating AMLs from RCCs as an AML will demonstrate high T1, low T2 signal while the opposite is true of RCCs.

Indications for intervention include suspicion of malignancy, spontaneous hemorrhage, pain, hematuria, and risk of rupture and other complications. Acute hemorrhage due to spontaneous rupture is the most common indication for embolization. Indications for intervention with asymptomatic tumors are less clear, although the risk of hemorrhage increases as the tumor enlarges. Some authors endorse intervention in tumors larger than 4 cm with radiologic evidence of large vascular aneurysms, women planning pregnancy, patients requiring prolonged anticoagulation, and patients with no rapid access to an appropriate medical care center.

Embolization has many advantages in the management of AMLs as it allows for preservation of functional renal parenchyma and obviates the need of surgery. Complications of embolization include abscess formation, pleural effusions, and nontarget embolization.