A 72-year-old male with long-standing atrial fibrillation and generalized atherosclerosis presents with severe, sudden-onset periumbilical abdominal pain for 4 hours. On physical examination, the abdomen is soft and non-tender with normal active bowel sounds. Serum lactate is 3.8 mmol/L, and WBC is 18,000/uL. What is the most likely diagnosis?

Answer and explanation

Correct answer: C. Acute Mesenteric Ischemia

  1. Step 1: The hallmark classic clinical presentation of Acute Mesenteric Ischemia is 'severe, agonizing abdominal pain out of proportion to physical examination findings' (pain is intense, but the abdomen remains soft without peritoneal signs in early stages).
  2. Step 2: Atrial fibrillation is the prime source of thromboemboli lodging in the superior mesenteric artery (SMA).
  3. Step 3: Elevated serum lactate reflects gut anaerobic metabolism and impending bowel infarction.
  4. Step 4: Urgent multiphasic mesenteric CT angiography (CTA) is the diagnostic test of choice.
Answer
Acute Mesenteric Ischemia.
Why not the others: 'Perforated diverticulitis' produces focal left lower quadrant peritonitis and guarding; 'Small bowel obstruction' features distension and high-pitched tinkling sounds; 'Renal colic' radiates to the groin with hematuria.

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