Discussion

Angiomyolipoma is a benign renal neoplasm composed of fat, vascular and smooth muscle elements. It has a prevalence of about 0.3–3%. Two types are described: isolated angiomyolipoma and angiomyolipoma associated with tuberous sclerosis. Isolated angiomyolipoma occurs sporadically, is often solitary and accounts for 80% of all angiomyolipomas.1 Shadowing on sonography is seen in 33% of acute myeloid leukaemias.2 3 In the general population in both sexes angiomyolipoma are most common in the age group 40–45 years. The mean age at presentation in patients with isolated angiomyolipoma is 43 years. This neoplasm is about four times more common in women than in men and interestingly 80% of cases involve the right kidney. Angiomyolipomas have thicker arteries than normal but abnormally weak vessel walls which predispose to aneurysm formation.4 Angiomyolipoma that is associated with tuberous sclerosis accounts for 20% of angiomyolipomas. The lesions are typically larger than isolated angiomyolipomas, and they are often bilateral and multiple. Angiomyolipomas occur in 80% of patients with tuberous sclerosis.1 The male-to-female distribution of angiomyolipoma in patients with tuberous sclerosis is almost equal. Angiomyolipomas occur in young women with lymphangiomyomatosis without other stigmata of tuberous sclerosis. Although angiomyolipomas are considered benign, rare cases that are possibly related to multicentric disease have been reported regarding extension into the renal vein, the inferior vena cava, or both; deposits in the regional lymph nodes have also been reported. The risk is probably very low in tumours that are <3 cm in diameter. Apart from this group with tuberous sclerosis, follow-up may be reasonably restricted to patients with sporadic tumours >4 cm in diameter, in whom the prevalence rate of haemorrhagic complications is higher. Thin section multidetector CT is the preferred method to demonstrate fat in problem cases (table 1).5