A problem in diagnostic imaging.

Many pathological processes can present as a swelling in the groin. We present a case of complex, ruptured pyonephrosis causing a psoas collection, which in turn presented clinically as an apparent right "incarcerated inguinal hernia." The patient was successfully treated with antibiotics and ultrasound-guided drainage of the abscess. The anatomical basis of the inguinal presentation of this complex pyonephrosis can be understood in the arrangement of the renal (Gerota's) fascia.