Abdominal CT Angiography (Answer: D)
The most appropriate investigation is abdominal CT angiography (CTA) with triple-phase imaging, as this patient's presentation is classic for acute mesenteric ischemia—a surgical emergency requiring immediate diagnosis. 1, 2
Clinical Reasoning
This patient has the pathognomonic triad for acute mesenteric ischemia (AMI):
- Atrial fibrillation - present in nearly 50% of embolic AMI cases and represents the most critical risk factor for mesenteric arterial embolism 1
- Pain out of proportion to examination - the hallmark clinical feature of AMI 1, 2
- Soft abdomen with decreased bowel sounds - indicates absence of peritoneal signs, suggesting potentially viable bowel with a window for revascularization 1
The unintentional weight loss may suggest chronic mesenteric ischemia progressing to acute thrombotic occlusion 1
Why CT Angiography is the Answer
- Triple-phase CTA (non-contrast, arterial, and portal venous phases) is the diagnostic test of choice recommended by the American College of Radiology for comprehensive evaluation of AMI 1, 2, 3
- CTA identifies arterial occlusion with 94% sensitivity and 95% specificity 1
- CTA evaluates bowel wall changes and viability, detects complications such as pneumatosis, portal venous gas, or perforation, and excludes alternative diagnoses 1
- In patients with atrial fibrillation presenting with acute abdominal pain, there is a 37% likelihood of CT findings related to atrial fibrillation, including end-organ ischemia or infarction (27%) 4
Why the Other Options Are Inadequate
- Lactate levels (Option A) - While lactate may be elevated in AMI, it is a late finding indicating bowel necrosis and is neither sensitive nor specific enough to guide initial diagnosis 1
- Plain X-ray (Option B) - The American College of Radiology gives plain X-ray a rating of "usually not appropriate" for evaluating intestinal ischemia due to limited diagnostic value and potential for false negatives 1
- Abdominal ultrasound (Option C) - Not adequate for evaluating mesenteric arterial occlusion or bowel viability in AMI 1, 2
Critical Time-Sensitive Considerations
- Time to diagnosis is the most important predictor of outcome, with mortality approaching 50% overall but improving dramatically with intervention within 5-10 hours of symptom onset 1
- Do not delay CTA for elevated creatinine, as the risk of missing mesenteric ischemia far outweighs contrast nephropathy concerns 1
- Immediate surgical consultation is required after CTA confirmation of AMI, regardless of imaging findings 1, 2
Management After Diagnosis
- Endovascular intervention (angiography with aspiration embolectomy or transcatheter thrombolysis) is preferred as first-line treatment for AMI without peritoneal signs 1, 2, 5
- Systemic anticoagulation should be initiated as adjunct therapy 1
- Long-term anticoagulation is necessary to prevent recurrent embolic events in patients with atrial fibrillation 2