Retropenal abcess secondary to a ruptured retrocecal appendix diagnosed by ultrasound B scan and 67 Ga radionulide scan.

Standard roentgenographic criteria for anterior-posterior (AP) displacement of the kidney may not reveal small, uniformly distributed, perirenal masses. Ultrasound, on the other hand, is an axial display and thus is quite sensitive to such changes. A case of ruptured retrocecal appendix is presented in which the intravenous pyelogram was negative. In the sonogram, however, a slight separation was seen between the renal parenchyma and the posterior abdominal muscle wall. This led to further investigation and the diagnosis of an unsuspected retrorenal abscess.