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Difficulty: HardOrdering Imaging Studies

A 74-year-old man is brought to the emergency department by his family due to the sudden onset of severe, unrelenting abdominal pain that began 22 hours ago. He reports the pain is diffuse, 10/1010/10 in intensity, and associated with one episode of non-bilious emesis. He has a history of hypertension, type 2 diabetes mellitus, and permanent atrial fibrillation. He was previously prescribed apixaban but stopped taking it three weeks ago because he could not afford the refill.

Vital signs are: temperature 37.2∘C37.2^\circ\text{C} (99.0∘F99.0^\circ\text{F}), blood pressure 105/65105/65 mmHg, pulse 118118/min and irregularly irregular, and respirations 2222/min.

Physical examination reveals a patient in obvious distress, writhing on the stretcher. Cardiopulmonary examination is unremarkable except for an irregularly irregular rhythm. Abdominal examination reveals a soft, non-distended abdomen with normal bowel sounds. There is diffuse mild tenderness to deep palpation, but no rebound, guarding, or rigidity is present.

Laboratory studies show:
Leukocyte count: 18,500/mm318,500/\text{mm}^3
Serum creatinine: 2.32.3 mg/dL (baseline 1.01.0 mg/dL)
Serum lactate: 4.84.8 mmol/L

Which of the following is the most appropriate next step in imaging?

  1. Computed tomography angiography of the abdomen and pelvisAnswer
  2. B
    Non-contrast computed tomography of the abdomen and pelvis
  3. C
    Catheter-directed digital subtraction angiography
  4. D
    Magnetic resonance angiography of the abdomen
  5. E
    Transthoracic echocardiography

Answer

Computed tomography angiography (CTA) of the abdomen and pelvis is the correct imaging choice.
The correct response identifies that computed tomography angiography (CTA) is the gold standard for the initial diagnosis of acute mesenteric ischemia. This patient's presentation—severe pain out of proportion to exam findings, an irregularly irregular pulse indicating atrial fibrillation off anticoagulation, and elevated lactate—makes SMA embolism highly likely. Rapid diagnosis is essential because bowel viability strictly depends on time to reperfusion. Even in the presence of acute kidney injury (creatinine 2.32.3 mg/dL), intravenous contrast must be administered because a non-contrast scan cannot reliably evaluate the mesenteric vessels. The threat to the patient's life from necrotic bowel supersedes the risk of contrast-induced kidney injury.

Step-by-Step Solution

1
Analyze the clinical presentation and risk factors.
The patient has sudden, severe abdominal pain that is out of proportion to the benign physical examination findings, alongside a history of atrial fibrillation and recent cessation of anticoagulation.
These findings are the classic triad for acute mesenteric ischemia, likely due to a superior mesenteric artery (SMA) embolus.
2
Interpret the laboratory findings in the context of the acute presentation.
Marked leukocytosis and elevated lactate strongly support bowel ischemia. The elevated creatinine indicates acute kidney injury (AKI).
Lactate is a marker of tissue hypoperfusion and anaerobic metabolism. The AKI is likely secondary to third-spacing, hypovolemia, or early sepsis.
3
Select the optimal diagnostic imaging study while weighing contraindications.
CTA of the abdomen and pelvis is selected. Intravenous contrast is administered despite the elevated creatinine.
In true life-threatening emergencies where withholding contrast would significantly delay or obscure a fatal diagnosis (like dead bowel), the risk of contrast-induced nephropathy is considered secondary. CTA is highly sensitive and specific for diagnosing mesenteric vascular occlusion.

Key Concept

Computed tomography angiography (CTA) is the initial imaging modality of choice for suspected acute mesenteric ischemia. In life-threatening emergencies, suspected contrast-induced nephropathy or acute kidney injury is not an absolute contraindication to the administration of intravenous contrast.

Alternative Method

If the patient presented with frank peritonitis (rigid abdomen, severe rebound tenderness) indicating that bowel infarction and perforation had already occurred, the correct next step would bypass imaging entirely in favor of an immediate exploratory laparotomy.
Estimated Time:1m 30s
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Ordering Imaging Studies

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