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Difficulty: MediumOrdering Imaging Studies

A 74-year-old man is brought to the emergency department due to the abrupt onset of severe abdominal pain that began 3 hours ago. He describes the pain as generalized and constant, with an intensity of 10/10. His medical history is significant for atrial fibrillation, hypertension, hyperlipidemia, and chronic kidney disease stage 3. He was prescribed apixaban but admits to missing multiple doses over the past week. His temperature is 37.3°C (99.1°F), blood pressure is 145/85 mm Hg, heart rate is 118/min and irregularly irregular, and respiratory rate is 22/min. On physical examination, the abdomen is soft and non-distended. There is mild, diffuse tenderness to deep palpation, but no guarding, rigidity, or rebound tenderness. Bowel sounds are decreased. Laboratory results are as follows:

Hemoglobin: 13.8 g/dL
Leukocyte count: 16,500/mm³
Platelet count: 240,000/mm³
Blood urea nitrogen: 42 mg/dL
Serum creatinine: 2.6 mg/dL (Baseline: 1.6 mg/dL)
Lactate: 4.5 mmol/L (Normal: 0.5–1.0 mmol/L)

Which of the following is the most appropriate next imaging study to establish the diagnosis?

  1. Computed tomography angiography of the abdomen and pelvisAnswer
  2. B
    Computed tomography of the abdomen and pelvis without intravenous contrast
  3. C
    Mesenteric duplex ultrasonography
  4. D
    Magnetic resonance angiography of the abdomen and pelvis
  5. E
    Catheter-directed mesenteric angiography

Answer

Computed tomography angiography of the abdomen and pelvis is the correct imaging study, as the life-threatening nature of suspected acute mesenteric ischemia outweighs the risks of contrast-associated acute kidney injury.
The correct answer is computed tomography angiography (CTA) of the abdomen and pelvis. This patient's presentation of abrupt-onset severe abdominal pain out of proportion to physical exam findings, especially in the setting of atrial fibrillation without adequate anticoagulation and an elevated lactate, is highly suspicious for acute mesenteric ischemia. CTA is the optimal initial diagnostic study because it is rapid, non-invasive, and highly sensitive for detecting mesenteric vessel occlusion and early signs of bowel ischemia. Crucially, while this patient has an acute kidney injury, the risk of contrast-associated acute kidney injury is heavily outweighed by the immediate threat to life. Withholding intravenous contrast in this scenario is a dangerous medical error that can delay life-saving surgical or endovascular intervention.

Step-by-Step Solution

1
Identify the primary clinical syndrome.
The patient presents with abrupt, severe abdominal pain that is out of proportion to the benign physical exam findings, accompanied by a history of atrial fibrillation off anticoagulation and an elevated lactate level.
To formulate the most likely working diagnosis, which in this case is acute mesenteric ischemia (AMI) likely due to a superior mesenteric artery embolus.
2
Determine the optimal initial diagnostic test for the suspected condition.
Computed tomography angiography (CTA) is the gold standard initial non-invasive test for AMI.
CTA provides rapid, highly sensitive evaluation of the mesenteric vessels, bowel wall enhancement, and can identify alternative causes of acute abdominal pain.
3
Evaluate for potential contraindications to the preferred test.
The patient has an acute kidney injury (creatinine 2.6 mg/dL, elevated from baseline), which is a relative contraindication to intravenous iodinated contrast.
To determine if the standard diagnostic protocol must be altered for patient safety.
4
Weigh the risks versus benefits of contrast administration.
The immediate need to confirm a highly lethal, time-sensitive diagnosis far outweighs the risk of contrast-associated acute kidney injury.
In true life-threatening emergencies (e.g., AMI, aortic dissection, ruptured AAA), contrast must not be withheld due to impaired renal function.

Key Concept

In life-threatening emergencies such as suspected acute mesenteric ischemia, the necessity of a definitive and rapid diagnosis via computed tomography angiography outweighs the relative contraindication of acute kidney injury for intravenous contrast administration.
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Ordering Imaging Studies

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