Echo-free and relatively echo-free "renal sinus lipomatosis".

Eleven echo-free and 37 relatively echo-free peripelvic lesions, primarily interpreted as sinus lipomatosis by experienced sonologists, were examined using CT. Eight echo-free lesions proved to be cysts and only three "fibrous fat". Hypodense peripelvic fat accumulations were not totally echo-free in any of the cases, but tended to show up weak echos.