The posterolateral and the retrorenal colon: implication in percutaneous stone extraction.

Increasing experience with percutaneous nephrolithotomy has fostered an aggressive approach to most renal calculi. We report a case of a stone in a horseshoe kidney. Computerized tomography before anticipated percutaneous stone extraction revealed the colon to be positioned posterior to the left portion of the horseshoe kidney. The posterior position of the colon prevented percutaneous access to the kidney. Computerized tomography should be performed in patients with stones in horseshoe kidneys and other fusion anomalies before elective percutaneous stone extraction is done.