Figure 5.

An axial section of unenhanced CT in a 25-year-old man with right renal colic. Initial ultrasonography showed left renal hydronephrosis. The CT (a) shows enlarged left psoas muscles (star) compared to the right psoas muscle. Subsequently contrast-enhanced CT (b) was used, which confirmed a psoas abscess (arrow) with enhancing margins (arrowhead) and inflammatory changes causing enlargement of the left psoas muscle. This was the cause of obstruction of the left ureter, resulting in left renal hydronephrosis, detected on ultrasonography (c).