The retrorenal colon in the supine and prone patient.

Ninety patients underwent computed tomographic scanning in both the supine and prone positions to show the orientation of the retroperitoneal colon about the kidneys and allow evaluation of changes in colonic position and contents. The data were compared with data on 500 patients scanned only when supine. Particular attention was given to bowel found posterior to the kidneys (retrorenal colon): its frequency of occurrence on 500 scans of supine patients was 1.9%, but 10.0% in the 90 prone patients. Because most invasive renal procedures would not intersect with retrorenal colon located behind the lateral one-third of the kidney, the data were reevaluated after deletion of these patients, giving a frequency in prone patients of 4.7%. This was found exclusively at the level of the lower renal poles, and the involved colon was extensively distended with gas. Attention should be given at fluoroscopy to detect this unusual, posteriorly positioned, air-filled colon before any invasive renal procedure.