Angiomyolipomas (AMLs) are hamartomatous lesions containing smooth muscle, blood vessels and mature adipose tissue.

AML occurs most frequently in the kidneys.

 This tumour has been reported in several other organs, including the liver, reproductive organs, skin, and retroperitoneum.

Gastrointestinal involvement is rare.

Cases have been reported in the colon, duodenum, stomach, and appendix.

These mesenchymal tumours  arise from the perivascular epithelioid cell (PEC), which may give rise to a variety of tumours and proliferations such as angiomyolipoma, lymphangiomyoma, lymphangiomyomatosis, clear cell myomelanocytic tumour of the falciform ligament/ligamentum teres, and pulmonary clear cell "sugar" tumour. 

Grossly, the tumour is yellow to gray depending on the relative proportion of the various tissue elements.

Histologically, the tumour consist of three components: mature fat cells, blood vessels, and smooth muscle cells.  Immunohistochemically, the proliferating smooth muscle cells are positive for vimentin, alpha-smooth muscle actin, and desmin.  

Angiomyolipomas also express the melanocytic markers HMB-45, MART-1 (Melan A), microphthalmia transcription factor, and tyrosinase. 

AML may be associated with Tuberous Sclerosis .

Although classic renal angiomyolipomas were regarded as universally benign lesions it is becoming increasingly clear that PEComas should be regarded as tumours of uncertain malignant potential.

 Tumours with a poor outcome are usually monotypic myomatous variants, especially those with dominant pleomorphic epithelioid components.

Factors likely to indicate poor outcome include presence of haemorrhage and necrosis, local invasiveness, and high mitotic activity.