Duodenal Obstruction Due to a Retroperitoneal Abscess Secondary to Pyelonephritis: A Rare but Significant Complication

A 74-year-old woman presented with a fever and profuse vomiting. Contrast-enhanced computed tomography (CT) showed a marked dilation of the stomach and proximal duodenum and a retroperitoneal abscess extending from the right ureter due to inflammatory spread. She was treated conservatively with nasogastric decompression and intravenous antibiotics, thus leading to a gradual resolution of both the obstruction and the abscess. This case highlights a rare but important complication of a urinary tract infection, emphasizing that extrinsic inflammatory etiologies should be considered in the differential diagnosis of duodenal obstruction, and that timely recognition may allow for successful conservative management without the need to perform any invasive procedures.