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Difficulty: Very hardOrdering Imaging Studies

A 72-year-old female resident of a skilled nursing facility is brought to the emergency department due to sudden, severe, diffuse abdominal pain that began three hours ago. Her medical history is significant for hypertension, type 2 diabetes mellitus, chronic kidney disease stage 4 (baseline serum creatinine 2.8 mg/dL, eGFR 18 mL/min/1.73m²), and paroxysmal atrial fibrillation. She is not currently taking anticoagulants due to a history of recurrent falls. On arrival, her temperature is 37.6°C (99.7°F), blood pressure is 105/65 mm Hg, pulse is 118/min and irregularly irregular, and respiratory rate is 22/min. Physical examination reveals a soft, non-distended abdomen with minimal tenderness to deep palpation; there is no guarding or rebound tenderness. Bowel sounds are hypoactive. Initial laboratory studies show a white blood cell count of 16,500/mm³ and a serum lactate level of 4.8 mmol/L. Which of the following is the most appropriate next step in diagnostic imaging?

  1. Computed tomography angiography of the abdomen and pelvisAnswer
  2. B
    Non-contrast computed tomography of the abdomen and pelvis
  3. C
    Mesenteric duplex ultrasonography
  4. D
    Magnetic resonance angiography of the abdomen
  5. E
    Postponement of cross-sectional imaging until after aggressive intravenous fluid resuscitation and repeat renal function testing

Answer

Computed tomography angiography of the abdomen and pelvis
The patient's presentation of severe abdominal pain out of proportion to physical exam findings, coupled with a history of atrial fibrillation (off anticoagulation) and elevated lactate, strongly suggests acute mesenteric ischemia (AMI). The definitive initial imaging modality for suspected AMI is a computed tomography angiography (CTA) of the abdomen and pelvis. Although the patient has severe chronic kidney disease (stage 4), the risk of fatal bowel necrosis far outweighs the risk of contrast-induced nephropathy. In life-threatening emergencies where timely diagnosis is critical for surgical intervention, contrast studies must not be withheld or delayed due to renal impairment.

Step-by-Step Solution

1
Analyze the clinical presentation and identify the most likely diagnosis.
The patient has severe abdominal pain out of proportion to physical exam findings, an irregular pulse (atrial fibrillation off anticoagulation), and elevated lactate, highly suspicious for acute mesenteric ischemia (AMI).
Recognizing the classic triad of AMI is essential to guide the urgency and type of subsequent diagnostic workup.
2
Determine the gold standard imaging modality for the suspected diagnosis.
Computed tomography angiography (CTA) of the abdomen and pelvis is the imaging test of choice for AMI.
CTA provides rapid, highly sensitive, and specific evaluation of the mesenteric vasculature to identify thromboembolic occlusion.
3
Evaluate potential contraindications to the preferred imaging modality.
The patient has stage 4 chronic kidney disease (eGFR 18 mL/min/1.73m²), which normally warrants caution with iodinated contrast due to the risk of contrast-induced nephropathy.
Assessing risks versus benefits is a core component of medical decision-making in complex patients.
4
Apply the 'life-over-limb/organ' principle to the clinical scenario.
The risk of bowel infarction and death from delayed diagnosis of AMI far outweighs the risk of contrast-induced acute kidney injury.
In true life-threatening emergencies where prompt surgical intervention may be required, relative contraindications to contrast media must be bypassed.

Key Concept

In life-threatening emergencies such as acute mesenteric ischemia, the diagnostic requirement for contrast-enhanced imaging (CTA) supersedes relative contraindications such as severe chronic kidney disease.
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Ordering Imaging Studies

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