Renal Angiomyolipoma
A renal angiomyolipoma (AML) is a benign kidney tumor made up of blood vessels, smooth muscle, and fat. Most AMLs are discovered incidentally on imaging and cause no symptoms. Although benign, larger angiomyolipomas can bleed or cause pain, especially if they contain aneurysms or grow rapidly. Some individuals have a single AML, while others may develop multiple AMLs, particularly in association with tuberous sclerosis complex (TSC).
What is it?
A renal angiomyolipoma is a benign kidney tumor composed of fat, muscle, and blood vessels. Most AMLs are sporadic, meaning they occur without an underlying disorder, and tend to remain stable. AMLs associated with tuberous sclerosis are often multiple and may grow larger. While benign, AMLs can sometimes bleed internally, especially if the tumor is larger than 4 cm or contains weak blood vessel walls.
CT and MRI are highly effective in identifying AMLs because they can detect the fat within the tumor, a key diagnostic feature. When the lesion has little or no visible fat (a “fat-poor AML”), further imaging or biopsy may be needed to distinguish it from other kidney tumors.
Important to Know
Most angiomyolipomas do not require treatment unless they are large, growing, or causing symptoms. Tumors larger than about 4 cm have a higher risk of bleeding and may be monitored more closely or treated preventively. AMLs related to tuberous sclerosis may behave differently and often require long-term monitoring.
Red flag symptoms include sudden severe flank pain, dizziness or fainting (possible bleeding), blood in the urine, or rapidly increasing abdominal size. These require prompt evaluation. Follow-up imaging is often recommended to monitor size and detect any changes early.