A 70-year-old male with a history of atrial fibrillation presents with sudden onset severe abdominal pain out of proportion to physical examination findings. An abdominal X-ray shows 'thumbprinting' of the colon and intramural gas (pneumatosis intestinalis). These findings are highly suggestive of:

Explanation

The clinical scenario (elderly patient, history of atrial fibrillation, sudden onset severe abdominal pain out of proportion to physical findings) is highly classic for mesenteric ischemia. The abdominal X-ray findings further support this diagnosis: 'Thumbprinting' refers to nodular indentations on the bowel wall caused by submucosal edema and hemorrhage, a characteristic sign of ischemia. Pneumatosis intestinalis (gas within the bowel wall) is a critical finding indicating transmural ischemia and impending or actual bowel infarction, often due to gas-producing bacteria in the compromised bowel wall. While toxic megacolon can show severe colonic dilation and loss of haustra, and can sometimes be a complication of severe ischemia, the combination of 'thumbprinting' and pneumatosis intestinalis in this clinical context points most directly to ischemic colitis. Ulcerative colitis flare and diverticulitis typically have different clinical and radiological presentations, although severe ulcerative colitis can lead to toxic megacolon.