An 76-year-old woman arrives at the emergency department accompanied by her daughter. The … — USMLE Step 3

An 76-year-old woman arrives at the emergency department accompanied by her daughter. The patient reports the abrupt onset of excruciating, generalized abdominal pain that started approximately $2$ hours ago. The pain is severe, constant, and associated with one episode of non-bilious emesis and an urgent need to defecate. Her medical history includes long-standing hypertension, type 2 diabetes mellitus, chronic kidney disease stage 4, and paroxysmal atrial fibrillation. She states she has not taken her prescribed apixaban for the past three weeks due to an insurance coverage issue.

Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure of $158/92 \text{ mmHg}$ , a heart rate of $115/\text{min}$ with an irregularly irregular rhythm, and a respiratory rate of $22/\text{min}$ . On physical examination, the patient appears in significant distress, writhing on the stretcher. Her abdomen is soft and non-distended. There is mild, diffuse tenderness to palpation, but no guarding, rigidity, or rebound tenderness is elicited. Bowel sounds are diminished.

Initial laboratory evaluation reveals:

Test	Result
Leukocyte count	$16,500/\text{mm}^3$
Hemoglobin	$11.4 \text{ g/dL}$
Platelet count	$215,000/\text{mm}^3$
Blood urea nitrogen	$52 \text{ mg/dL}$
Serum creatinine	$3.4 \text{ mg/dL}$ (baseline $2.5 \text{ mg/dL}$ )
Lactate	$4.9 \text{ mmol/L}$

Which of the following is the most appropriate next step in diagnostic imaging for this patient?

Computed tomography angiography of the abdomen and pelvisAnswer
B
Non-contrast computed tomography of the abdomen and pelvis
C
Magnetic resonance angiography of the abdomen
D
Mesenteric duplex ultrasonography
E
Upright and supine abdominal radiography

Answer

Computed tomography angiography of the abdomen and pelvis

The correct answer is computed tomography angiography (CTA) of the abdomen and pelvis. This patient's presentation of abrupt, severe abdominal pain that is out of proportion to physical examination findings, combined with atrial fibrillation off anticoagulation and an elevated lactate level, is highly suspicious for acute mesenteric ischemia (likely embolic). CTA is the rapid, non-invasive imaging modality of choice to establish this diagnosis, allowing for direct visualization of the mesenteric vasculature. A critical teaching point in this scenario is managing the patient's acute kidney injury on chronic kidney disease. While intravenous iodinated contrast carries a risk of contrast-associated acute kidney injury, acute mesenteric ischemia is a life-threatening, time-sensitive emergency with a very high mortality rate. The American College of Radiology guidelines dictate that intravenous contrast must never be withheld in life-threatening situations where the diagnosis depends on it.

Step-by-Step Solution

Identify the primary clinical syndrome based on history and physical exam.

The patient has severe abdominal pain out of proportion to physical exam findings, an irregular rhythm (atrial fibrillation) while off anticoagulation, and an elevated lactate level.

These findings are classic for acute mesenteric ischemia, likely due to an arterial embolus from the heart.

Determine the optimal diagnostic imaging for the suspected condition.

Computed tomography angiography (CTA) is the gold standard for diagnosing acute mesenteric ischemia.

CTA provides rapid, high-resolution imaging of the mesenteric vasculature to identify occlusions.

Evaluate potential contraindications to the preferred imaging study.

The patient has an acute kidney injury superimposed on chronic kidney disease stage 4, which normally warrants caution with intravenous contrast.

Intravenous contrast can cause contrast-associated acute kidney injury.

Weigh the risks and benefits of contrast administration in this specific clinical context.

The risk of contrast-associated acute kidney injury is superseded by the high mortality rate of untreated acute mesenteric ischemia.

In life-threatening emergencies where a definitive diagnosis dictates immediate surgical or endovascular intervention, life-saving imaging with contrast must not be delayed or withheld.

Key Concept

In patients with suspected acute mesenteric ischemia, computed tomography angiography (CTA) is the initial imaging modality of choice. Intravenous contrast should not be withheld due to renal impairment in life-threatening emergencies.

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