Variations of the position of the colon as applied to percutaneous nephrostomy

The widespread and increasing usage of percutaneous nephrostomy procedures makes an awareness of the anatomical variations of the colon in relation to the kidney essential. Injury to the colon during this procedure is associated with significant morbidity. The aim of this study was to determine the relation of the colon to the insertion line used during a percutaneous nephrostomy and therefore determine whether the colon is at risk of injury. 333 CT-scans taken in a supine position were studied in order to determine the position of both the ascending and descending colon to the percutaneous nephrostomy insertion line on the level of the superior pole, hilum and inferior pole of the kidneys. In the majority of cases, the ascending and descending colon lie anterior to the line of insertion, and were therefore not at risk. However the descending colon was found to be at risk in 16.1% of cases and the ascending colon in 9.0% of cases on the level of the inferior pole of the kidney. The risk was significantly lower on the level of the hilum and superior pole of the kidneys on both sides. Age distribution analysis showed that the colon is rarely at risk under twenty years of age and the highest risk being in the age range above 40 years. Adequate radiographic evaluation is essential before performance of percutaneous nephrostomy procedures, especially to evaluate the position of the colon as related to the inferior poles of the kidneys.