Renal angiomyolipomas (AML) are a type of benign renal neoplasm encountered both sporadically and as part of a phakomatosis, most commonly tuberous sclerosis. They are considered one of a number of tumours with perivascular epitheloid cellular differentiation (PEComas) and are composed of vascular, smooth muscle and fat elements. They can spontaneously haemorrhage, which can be fatal. AMLs usually have characteristic radiographic appearances2.
The cornerstone of diagnosis on all modalities is the demonstration of macroscopic fat, however in the setting of haemorrhage, or when lesions happen to contain little fat, it may be difficult to distinguish an AML from a renal cell carcinoma3.
The sonographic features are:
- Tend to appear as hyperechoic lesions on ultrasound, located in the cortex and with posterior acoustic shadowing4.
- In the setting of tuberous sclerosis, they may be so numerous that the entire kidney is affected, appearing echogenic with the loss of normal corticomedullary differentiation4.
- Contrast-enhanced ultrasound5:
* tend to enhance peripherally.
* decreased central enhancement, compared with normal cortex.
Angiomyolipomas found incidentally usually require no therapy (when small), although follow-up is recommended to assess for growth. Small solitary AMLs (< 20 mm) probably do not require follow-up due to their slow growth6.
Larger AMLs, or those that have been symptomatic, can be electively embolised and/or resected with a partial nephrectomy. Lesions that present with retroperitoneal haemorrhage often requires emergency embolisation as a life-saving measure. mTOR inhibitors (e.g. everolimus) have been shown to significantly decrease AML size and may help to preserve renal function in tuberose sclerosis patients3.