Gallbladder Volvulus Mimicking Immune Checkpoint Inhibitor-Related Acalculous Cholecystitis: A Case Report.

Gallbladder volvulus (GV) is a rare surgical emergency whose clinical and radiological presentation closely mimics acute cholecystitis. This diagnostic difficulty is amplified in patients receiving immune checkpoint inhibitors (ICIs), as gallbladder inflammation may initially be misattributed to an immune-related adverse event (irAE). We report the case of an 82-year-old woman with microsatellite instability-high (MSI-H) duodenal adenocarcinoma treated with pembrolizumab. Following a temporary discontinuation of immunotherapy and initiation of corticosteroids for a suspected gastrointestinal irAE, she presented with acute right upper quadrant pain. Computed tomography (CT) showed a markedly distended, displaced gallbladder with absent mural enhancement. Initially suspected to be ICI-related cholecystitis, emergency laparoscopy instead revealed a >180° GV with transmural ischemic necrosis. A retrospective CT review identified a subtle cystic-pedicle "whirl sign." Following laparoscopic cholecystectomy, the patient recovered uneventfully, and pembrolizumab was later resumed. GV should remain in the differential diagnosis of acute acalculous cholecystitis in elderly patients, even those on immunotherapy. A plausible immune-mediated explanation should not lead to diagnostic anchoring when clinical and radiological signs - such as ischemia or a whirl sign - indicate an acute mechanical surgical emergency.