An angiomyolipoma is a benign fatty tumor that can form in kidneys. They are made up of muscle and vessels as well as fatty tissue. The incidence rate in the general population is about 0.3%, although that figure is much higher when associated with a condition called tuberous sclerosis. Most of these tumors are harmless and are isolated cases that do not recur although, very rarely, one can become cancerous or cause hemorrhaging.
About 80% of angiomyolipomas develop spontaneously in the absence of any other disease. More than half of tumors do not cause any symptoms, with symptoms more likely to occur if the tumor approaches or exceeds 1.6 inches (4 cm) in size. They usually are non-threatening, but larger tumors can cause potentially serious symptoms. For an unknown reason, about 80% form in the right kidney.
Most tumors grow without any underlying cause, but people with a genetic condition called tuberous sclerosis are at increased risk of developing an angiomyolipoma. This rare disease causes tumors to grow in many organs, including the brain, heart, lungs and skin, in addition to the kidneys. Up to 80% of people with tuberous sclerosis develop one or more on the kidneys, which are also called renal angiomyolipomas.
As the fatty tumor grows larger, it can cause abdominal pain, fever, nausea and weight loss. These symptoms are much more likely to occur in people who have tuberous sclerosis, as they generally occur when tumors are very large or when multiple tumors are present. Large tumors are at risk of hemorrhaging, which is potentially life-threatening.
Small, isolated tumors are unlikely to cause symptoms and might remain undiagnosed altogether. They often are diagnosed only when a patient undergoes a medical imaging scan for an unrelated condition. Those that are associated with tuberous sclerosis are more likely to be diagnosed, because people with this condition undergo regular medical imaging tests for screening purposes.
Asymptomatic tumors need not be treated as long as they remain small, but a larger tumor might need to be removed to prevent hemorrhaging. Angiomyolipomas are prone to spontaneous hemorrhage once they reach a certain size because the walls of blood vessels in these tumors are structurally weak. Rarely, a kidney might need to be removed altogether; this usually is carried out only in someone with tuberous sclerosis and when a kidney contains multiple tumors.
An alternative treatment, called transcatheter arterial embolization, might sometimes be carried out in preference to kidney removal. In this procedure, an artery that feeds the kidney is catheterized, and a substance that causes blood vessels to coagulate is fed into the tumor to prevent hemorrhaging. This option is used only when someone with tuberous sclerosis has multiple renal tumors and is not carried out in cases of spontaneous isolated ones.