A rare complication of the duodenal diverticulum.

UNLABELLED: Introduction: An 80-year-old woman presented to the emergency department with severe right-sided abdominal pain that had started after her last meal. Physical examination revealed fever (38.6°C) and rebound tenderness in the right upper quadrant of the abdomen. The laboratory studies showed a leucocyte count of 11.3×109/L (normal, 3.7-8.0×109/L) and a C-reactive protein level of 2.34 mg/dL (normal, <0.03 mg/dL). There were no other significant findings. A CT scan of the abdomen with contrast revealed retroperitoneal air around a duodenal diverticulum (figures 1 and 2).Figure 1Computed tomography scan of the abdomen with contrast (coronal section). A diverticulum in the second portion of the duodenum (arrow) and retroperitoneal air (asterisk) are shown.Figure 2Computed tomography scan of the abdomen with contrast (axial section). The area with retroperitoneal air (asterisk) is marked.

QUESTION: What is the most likely diagnosis and the cause underlying the condition?