What proportion are sporadic? What condition are the rest associated with?
80%. Tuberous sclerosis.
What is the most common and serious complication?
Spontaneous retroperitoneal haemorrhage.
What is the differential diagnosis?
Depends on amount of fat. When fat is abundant consider retroperitoneal liposarcoma invading the kidney and adrenal myelolipoma. As AMLs can be fat-poor, and many renal masses have been reported as containing fat the differential is sometimes broad and includes renal cell carcinoma (RCC), oncocytoma and even Wilms tumour which rarely can contain fat.
Pre and post contrast CT through the kidneys demonstrates a large fatty mass arising from the lateral aspect of the right kidney. There is a very prominent vessel centrally associated with central areas of soft tissue attenuation, some of which enhance, but other areas do not. These presumably represent areas of haemorrhage.