Lateral Duodenal Diverticulitis Mimicking a Right Retroperitoneal Collection: A Case Report.

Giant duodenal diverticula are rare and often asymptomatic but may present with atypical clinical and imaging findings that resemble intra-abdominal or retroperitoneal collections, abscesses, or cystic neoplasms. We report the case of a 67-year-old male who presented with recurrent right-sided abdominal symptoms initially treated as pyelonephritis and subsequently diagnosed as a right retroperitoneal abscess. Further evaluation with multimodal imaging, including contrast-enhanced computed tomography (CECT) with oral contrast and retrospective ultrasound review, revealed a giant duodenal diverticulum communicating with the second part of the duodenum. Accurate interpretation of these findings allowed revision of the diagnosis and prevented unnecessary percutaneous drainage, thereby avoiding potential iatrogenic complications. The patient was managed conservatively with intravenous antibiotics and demonstrated clinical improvement, with endoscopic evaluation planned for further assessment. This case highlights the value of careful multimodal imaging correlation in avoiding inappropriate invasive procedures and informing optimal patient management.