A 76-year-old woman is brought to the emergency department by her family due to the sudden… — USMLE Step 3

A 76-year-old woman is brought to the emergency department by her family due to the sudden onset of severe abdominal pain that began 4 hours ago. The patient has a history of paroxysmal atrial fibrillation, for which she was prescribed apixaban but admits to missing multiple doses over the past week. She also has stage 3b chronic kidney disease and hypertension.

On arrival, her temperature is $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ ), blood pressure is $92/58 \text{ mmHg}$ , pulse is $128/\text{min}$ and irregularly irregular, and respiratory rate is $22/\text{min}$ . Physical examination reveals a soft, non-distended abdomen with only mild, diffuse tenderness to deep palpation. There is no guarding, rigidity, or rebound tenderness. Bowel sounds are absent.

Laboratory studies show:
Leukocyte count: $18,500/\text{mm}^3$
Hemoglobin: $12.2 \text{ g/dL}$
Serum creatinine: $2.1 \text{ mg/dL}$ (baseline $1.8 \text{ mg/dL}$ )
Serum lactate: $6.8 \text{ mmol/L}$ (Normal: $0.5 - 1.0 \text{ mmol/L}$ )

Due to concerns regarding her acute-on-chronic kidney injury, a non-contrast computed tomography (CT) scan of the abdomen and pelvis is performed. The radiologist reports diffuse bowel wall thickening involving the jejunum and proximal ileum. Additionally, there are linear gas collections within the wall of the affected small bowel segments, and branching, tubular areas of gas extending to the periphery of the right hepatic lobe.

Based on the imaging findings, which of the following is the most appropriate next step in management?

Emergent exploratory laparotomyAnswer
B
Computed tomography angiography of the abdomen and pelvis
C
Initiation of therapeutic intravenous heparin and admission to the intensive care unit
D
Endoscopic retrograde cholangiopancreatography
E
Endoscopic evaluation of the upper and lower gastrointestinal tracts

Answer

Emergent exploratory laparotomy

The patient's clinical presentation is highly suspicious for acute mesenteric ischemia (AMI) secondary to an arterial embolus from atrial fibrillation. The non-contrast CT scan demonstrates linear gas collections within the bowel wall (pneumatosis intestinalis) and branching gas in the periphery of the liver (portal venous gas). These imaging findings are pathognomonic for transmural bowel infarction. When transmural necrosis is present, the patient requires an emergent exploratory laparotomy for resection of the nonviable bowel. Attempting to obtain further confirmatory imaging at this stage is a common pitfall that critically delays definitive surgical care.

Step-by-Step Solution

Analyze the clinical presentation.

The patient has sudden, severe abdominal pain out of proportion to physical exam findings, with a history of medication-noncompliant atrial fibrillation, highly suggesting acute mesenteric ischemia.

Atrial fibrillation predisposes to mural thrombus formation, which can embolize to the superior mesenteric artery (SMA).

Interpret the specific radiologic findings.

Linear gas in the bowel wall (pneumatosis intestinalis) and branching gas in the liver periphery (portal venous gas) are identified.

When ischemia progresses to transmural necrosis, the mucosal barrier breaks down, allowing intraluminal gas-forming bacteria to enter the bowel wall and subsequently track through the mesenteric veins into the portal venous system.

Determine the appropriate management based on the imaging.

Emergent exploratory laparotomy is required.

The presence of pneumatosis intestinalis and portal venous gas indicates that the bowel is already dead. Definitive treatment is immediate surgical resection of the necrotic segments; further diagnostic imaging or medical management is contraindicated as it delays life-saving surgery.

Key Concept

In the setting of acute mesenteric ischemia, imaging findings of pneumatosis intestinalis and portal venous gas indicate transmural bowel necrosis and mandate immediate exploratory laparotomy, bypassing further diagnostic studies.

Estimated Time:1m 30s

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