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Difficulty: MediumOrdering Imaging Studies

A 42-year-old woman comes to the emergency department complaining of severe, constant right upper quadrant abdominal pain that began 18 hours ago after eating a large, high-fat meal. The pain radiates to her right scapula and is associated with nausea and two episodes of vomiting. She has no significant past medical history and takes no medications. Her temperature is 38.3∘C38.3^\circ\text{C} (100.9°F), heart rate is 102/min, blood pressure is 130/80 mmHg, and respiratory rate is 18/min. Physical examination reveals focal tenderness in the right upper quadrant with voluntary guarding, and inspiratory arrest occurs upon deep palpation of the right upper quadrant. Laboratory studies reveal a leukocyte count of 14,500/mm314,500/\text{mm}^3. Aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total bilirubin, and lipase levels are all within normal limits. A comprehensive right upper quadrant abdominal ultrasound is performed. It demonstrates the presence of multiple gallstones within the gallbladder, but there is no gallbladder wall thickening, no pericholecystic fluid, and the common bile duct measures 4 mm in diameter. The sonographer notes that the sonographic Murphy sign is equivocal. Which of the following is the most appropriate next step in imaging for this patient?

  1. CholescintigraphyAnswer
  2. B
    Computed tomography of the abdomen with intravenous contrast
  3. C
    Endoscopic ultrasonography
  4. D
    Magnetic resonance cholangiopancreatography
  5. E
    Plain radiography of the abdomen

Answer

Cholescintigraphy is the most appropriate next step in imaging.
The correct answer is cholescintigraphy (hepatobiliary iminodiacetic acid or HIDA scan). This patient's clinical presentation (fever, right upper quadrant pain radiating to the scapula, focal tenderness, leukocytosis) is highly suggestive of acute cholecystitis. The initial imaging test of choice for suspected acute cholecystitis is a right upper quadrant abdominal ultrasound, which typically shows gallstones, gallbladder wall thickening (greater than 4 mm), pericholecystic fluid, and a positive sonographic Murphy sign. However, in this patient, the ultrasound is equivocal (gallstones are present, but there is no wall thickening or pericholecystic fluid, and an equivocal sonographic Murphy sign). When the clinical suspicion for acute cholecystitis remains high despite a non-diagnostic or equivocal initial ultrasound, the most appropriate next step in imaging is cholescintigraphy. During this scan, a radiotracer is injected intravenously, taken up by the liver, and excreted into the biliary tree. In acute cholecystitis, the cystic duct is obstructed by a gallstone, which prevents the radiotracer from entering the gallbladder. Therefore, non-visualization of the gallbladder on a HIDA scan is diagnostic for acute cholecystitis.

Step-by-Step Solution

1
Evaluate the clinical presentation.
The patient has symptoms and signs highly suspicious for acute cholecystitis (fever, right upper quadrant pain, leukocytosis, positive physical exam findings).
Establishing the pre-test probability guides the diagnostic imaging algorithm.
2
Analyze the results of the initial imaging study.
The initial right upper quadrant ultrasound shows gallstones but lacks definitive inflammatory signs (no wall thickening or pericholecystic fluid) and has an equivocal sonographic Murphy sign.
Ultrasound is the best initial test, but its results determine if further imaging is needed.
3
Determine the next best imaging step based on the equivocal initial results.
Select cholescintigraphy (HIDA scan) to definitively confirm or rule out cystic duct obstruction.
Cholescintigraphy has high sensitivity and specificity for acute cholecystitis and is the standard of care when ultrasound is non-diagnostic but clinical suspicion remains high.

Key Concept

When clinical suspicion for acute cholecystitis is high but initial abdominal ultrasound is equivocal, cholescintigraphy (HIDA scan) is the most appropriate next diagnostic imaging step.
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Topics

Ordering Imaging Studies

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