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Difficulty: HardInterpreting Imaging Results

A 78-year-old woman is brought to the emergency department from an assisted living facility due to a 3-day history of progressively worsening nausea, intractable vomiting, and abdominal distension. Her medical history includes coronary artery disease, hypertension, and symptomatic cholelithiasis for which she declined surgery two years ago. Temperature is 37.7°C (99.9°F), blood pressure is 108/68 mm Hg, pulse is 104/min, and respirations are 18/min. Physical examination reveals a distended and tympanic abdomen with high-pitched, hyperactive bowel sounds. There is diffuse mild tenderness but no guarding or rebound. A non-contrast computed tomography (CT) scan of the abdomen and pelvis reveals markedly dilated loops of small bowel measuring up to 4.5 cm in diameter. A distinct transition point is visualized in the terminal ileum, immediately proximal to a 3.5-cm, round, hyperdense laminated structure. Additionally, branching tubular lucencies are noted within the liver parenchyma; these lucencies are predominantly centrally located near the hepatic hilum. Based on these imaging findings, which of the following is the most appropriate next step in management?

  1. Exploratory laparotomy and enterolithotomyAnswer
  2. B
    Computed tomography angiography of the mesenteric vessels
  3. C
    Nasogastric tube decompression and conservative observation
  4. D
    Percutaneous cholecystostomy
  5. E
    Endoscopic retrograde cholangiopancreatography

Answer

Exploratory laparotomy and enterolithotomy
The correct answer accurately addresses the diagnosis of gallstone ileus. The patient's CT scan demonstrates Rigler triad: small bowel obstruction, an ectopic radiopaque gallstone in the terminal ileum, and pneumobilia (air in the biliary tree). Pneumobilia is characterized by central branching lucencies in the liver, as opposed to portal venous gas, which is typically found in the hepatic periphery. Gallstone ileus is a mechanical bowel obstruction caused when a large gallstone (typically >2.5 cm) erodes through the gallbladder wall into the adjacent gastrointestinal tract (cholecystoenteric fistula) and impacts in the narrowest part of the small bowel, the terminal ileum. The definitive treatment for gallstone ileus is an exploratory laparotomy with enterolithotomy to extract the stone and relieve the obstruction.

Step-by-Step Solution

1
Interpret the abdominal CT findings.
Identified dilated small bowel with a transition point at the terminal ileum (mechanical small bowel obstruction), a 3.5-cm hyperdense laminated structure (gallstone), and central hepatic branching lucencies (pneumobilia).
Accurate interpretation of imaging is required to formulate the correct diagnosis and exclude mimics like mesenteric ischemia.
2
Differentiate pneumobilia from portal venous gas.
Recognized that the lucencies are central (near the hilum), characteristic of pneumobilia, whereas portal venous gas is typically peripheral.
This distinction confirms a biliary-enteric fistula rather than necrotic/ischemic bowel.
3
Synthesize the findings to establish a diagnosis.
Diagnosed gallstone ileus based on the presence of Rigler triad (pneumobilia, small bowel obstruction, and ectopic gallstone).
Gallstone ileus occurs when a large stone erodes through the gallbladder wall into the duodenum and impacts at the narrowest portion of the bowel (terminal ileum).
4
Determine the definitive management.
Selected exploratory laparotomy and enterolithotomy.
A 3.5-cm stone will not pass spontaneously; surgical extraction is required to relieve the mechanical obstruction.

Key Concept

Rigler triad on CT imaging (pneumobilia, small bowel obstruction, and ectopic gallstone) indicates gallstone ileus, which requires prompt surgical intervention (enterolithotomy) to relieve the obstruction.
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Interpreting Imaging Results

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