Uncommon Cause of Bile Duct Dilation: A Case of Duodenal Diverticulum Compressing the Lower Common Bile Duct (Lemmel's Syndrome)

Lemmel's syndrome is a rare and often underdiagnosed condition characterized by the compression of the common bile duct by a duodenal diverticulum, leading to the dilation of both intra- and extra-hepatic bile ducts. We present the case of a 55-year-old woman with unexplained bile duct dilation, where imaging studies, including biliary MRI (bili-IRM), revealed a duodenal diverticulum compressing the lower common bile duct. The patient was initially suspected to have obstructive cholangiopathy, but further evaluation through bili-IRM confirmed the diagnosis of Lemmel's syndrome. This case highlights the importance of considering Lemmel's syndrome in patients with unexplained biliary dilation, especially in the absence of identifiable stones or tumors. Timely recognition and differentiation of this rare condition from more common bile duct pathologies are crucial to avoid unnecessary interventions. The case is discussed in the context of its clinical presentation, diagnostic challenges, and management strategies.