Angiomyolipomas are the most common benign tumour of the kidney. Although regarded as benign, angiomyolipomas may grow such that kidney function is impaired or the blood vessels may dilate and burst, leading to bleeding. Angiomyolipomas are strongly associated with the genetic disease Tuberous Sclerosis, in which most individuals have several Angiomyolipomas affecting both kidneys. They are also commonly found in women with the rare lung disease lymphangioleiomyomatosis. Angiomyolipomas are less commonly found in the liver and rarely in other organs. Whether associated with these diseases or sporadic, Angiomyolipomas are caused by mutations in either the TSC1 or TSC2 genes, which govern cell growth and proliferation. They are composed of blood vessels, smooth muscle cells, and fat cells. Large Angiomyolipomas can be treated with embolisation. Drug therapy for Angiomyolipomas is at the research stage. The Tuberous Sclerosis Alliance has published guidelines on diagnosis, surveillance, and management. Signs and symptoms Most people with benign Angiomyolipomas do not show signs or have symptoms. However, some people can have symptoms If the dilated blood vessels in an Angiomyolipoma rupture, this is called a retroperitoneal hemorrhage. This can cause pain in the back, nausea and vomiting. Some long-term effects are anemia, hypertension, and chronic kidney disease. Up to 20% of patients who present symptoms, and are brought into the emergency department, are in shock. Pathophysiology Angiomyolipomas are tumours consisting of perivascular epithelioid cells (cells which are found surrounding blood vessels and which resemble epithelial cells). A tumour of this kind is known as a PEComa, from the initials of perivascular epithelioid cell. Older literature may classify them as hamartomas (benign tumours consisting of cells in their correct location, but forming a disorganised mass) or choristoma (benign tumours consisting of normal cells in the wrong location). PEComas are themselves a kind of mesenchymal tumour which involves cells that form the connective tissue, cardiovascular, and lymphatic systems. An Angiomyolipoma is composed of varying proportions of vascular cells, immature smooth muscle cells, and fat cells. These three components respectively give rise to the components of the name: angio-, myo-, and lip-. The -oma suffix indicates a tumour. Angiomyolipomas are typically found in the kidney, but have also been commonly found in the liver and less commonly the ovary, fallopian tube, spermatic cord, palate, and colon. The Maclean imaging classification system for renal Angiomyolipomas is based on the location of the Angiomyolipoma within the kidney. Since all three components