An Extreme Case of Retrorenal Colon

Abstract

An Extreme Case of Retrorenal Colon An 84-year-old woman with a remote history of cholecystectomy was referred for investigation of intermittent right lower quadrant fullness and discomfort. Abdominal CT performed with the patient supine with positive oral and IV contrast material revealed extreme posterior and retrorenal positioning of the ascending and descending colon, wrapping around the lower pole of the kidneys and extending almost to the posterolateral border of the psoas muscles (Fig. 1). Retrorenal positioning of the colon, as determined by a line drawn coronally through the posterior margin of the kidney, has been reported variably in 1–14% of the population [1, 2]. Normally, the ascending and descending colon lie anterior to the kidneys in the anterior pararenal space, which is bordered anteriorly by the posterior parietal peritoneum, posteriorly by the anterior renal (Gerota’s) fascia, and posterolaterally by the lateroconal fascia (formed by the fusion of the anterior and posterior renal fascia at their lateral borders). Two theories have been proposed for the normal variant of the retrorenal colon. The first theory is that the more lateral and posterior colonic positioning is a result of a smaller amount of perinephric fat [3]. The second is that the absence of the lateroconal fascia, or its formation more posteromedially, may allow the colon to extend around the posterior margin of the perirenal space [1]. The retrorenal position of the colon places the colon at risk for iatrogenic trauma during percutaneous procedures directed at the kidneys such as biopsy, percutaneous nephrostomy, and nephrolithotomy. The frequency of retrorenal colon was found to be five times higher when patients were positioned prone (the favored position for percutaneous procedures) rather than supine [4]. It has been suggested that the prone positioning results in a more gas-distended colon, which might more easily displace the renal fascia and possibly even dissect between the laminae of the posterior renal fascia. Chan R, Li DKB Ryan Chan University of Ottawa Ottawa, ON, Canada