Emphysematous pyelonephritis with perinephric extension and fistulous communication to the descending colon: a rare CT imaging diagnosis.

Emphysematous pyelonephritis (EPN) is a severe necrotizing infection characterized by gas formation within the renal parenchyma and surrounding tissues. Although perinephric extension is well recognized, fistulous communication with the adjacent bowel is exceedingly rare. We report a case of a 58-year-old woman presenting with fever, left flank pain, uncontrolled diabetes mellitus, and acute kidney injury. Initial non-contrast CT KUB showed left EPN with a large perinephric air-containing collection and loss of fat planes with the adjacent descending colon, raising suspicion of a reno-colic fistula. Following DJ stenting, a repeat CT scan with administration of rectal contrast demonstrated direct contrast leakage into the perinephric collection, confirming fistulous communication. Subsequent colonoscopy corroborated the imaging findings. This case highlights the importance of sequential CT imaging and the role of rectal contrast in confirming rare fistulous complications of EPN.