CT scanning in the diagnosis and management of radiolucent urinary calculi.

The diagnosis of non-opaque calculi can be difficult. In 4 patients with protracted symptoms, 2 had renal pelvic filling defects, 1 a possible filling defect and 1 complete obstruction of the ureter at L4. Non-opaque calculi were readily diagnosed by CT scanning. Three patients have successfully undergone surgery (2 open, 1 percutaneous) and 1 awaits percutaneous nephrolithotomy. Of two stones available for analysis, one was composed of uric acid and the other calcium and phosphate. We recommend CT scanning as the investigation of choice for unexplained filling defects in the renal pelvis and ureter or when a non-opaque calculus is suspected.