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Figure 24b.   Avulsion of the ureteropelvic junction (category IV) in a 49-year-old man who had sustained blunt trauma. (a, b) Contrast-enhanced nephrographic-phase helical CT scans (a obtained at a higher level than b) through the lower pole of the right kidney demonstrate a perinephric fluid collection with no renal laceration. (c, d) Contrast-enhanced excretory-phase CT scans (c obtained at a higher level than d) demonstrate medial contrast material extravasation (arrow). No ureteral contrast material filling is noted. The patient underwent exploratory laparotomy for a mesenteric laceration. A diagnosis of ureteropelvic junction avulsion was made, and primary surgical repair of the ureter was performed.