Angiomyolipoma (AML) are the most common benign tumour of the kidney and are composed of blood vessels, smooth muscle cells and fat cells. Angiomyolipoma are strongly associated with the genetic disease tuberous sclerosis, in which most individuals will have several angiomyolipoma affecting both kidneys. They are also commonly found in women with the rare lung disease lymphangioleiomyomatosis. Angiomyolipoma are less commonly found in the liver and rarely in other organs. Whether associated with these diseases or sporadic, angiomyolipoma are caused by mutations in either the TSC1 or TSC2 genes, which govern cell growth and proliferation.
Although regarded as benign, angiomyolipoma may grow such that kidney function is impaired or the blood vessels may dilate and burst leading to haemorrhage. Large angiomyolipoma can be treated with embolisation. Drug therapy for angiomyolipoma is at the research stage.Angiomyolipoma in both kidneys (arrows) in computer tomography. The tumours are hypodense (dark) due to fat content
There are three methods of scanning that detect angiomyolipoma: ultrasound, CT and MRI. Ultrasound is standard and is particularly sensitive to the fat in angiomyolipoma but less so to the solid components. However it is hard to make accurate measurements with ultrasound. Computed tomography (CT) is very detailed and fast and allows accurate measurement. However, it exposes the patient to radiation and the dangers that a contrast dye used to aid the scanning may itself harm the kidneys. Magnetic resonance imaging (MRI) is safer than CT but many patients (particularly those with the learning difficulties or behavioural problems found in tuberous sclerosis) require sedation or general anaesthesia and the scan cannot be performed quickly. Some other kidney tumours contain fat, so the presence of fat isn’t diagnostic. It can be difficult to distinguish a fat-poor angiomyolipoma from a renal cell carcinoma and a lesion growing at greater than 5 mm per year may warrant a biopsy in order to distinguish it from a from this form of cancer.