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Difficulty: MediumOrdering Imaging Studies

A 48-year-old woman comes to the emergency department complaining of severe, constant epigastric pain that began 8 hours ago. The pain radiates directly to her mid-back and is accompanied by persistent nausea and multiple episodes of non-bilious vomiting. She has no significant past medical history and takes no medications. She consumes a glass of wine occasionally but denies heavy alcohol use. Her temperature is 37.9°C (100.2°F), blood pressure is 135/85 mmHg, pulse is 108/min, and respiratory rate is 18/min. Physical examination reveals a non-distended abdomen with marked tenderness to palpation in the epigastrium; there is no rebound tenderness or guarding. Bowel sounds are hypoactive.

Laboratory evaluation shows:
Leukocyte count: 12,500/mm³
Serum alanine aminotransferase (ALT): 185 U/L
Serum aspartate aminotransferase (AST): 140 U/L
Serum alkaline phosphatase: 160 U/L
Serum lipase: 3,200 U/L (Reference range: 10-140 U/L)

Which of the following is the most appropriate initial imaging study for this patient?

  1. A
    Computed tomography of the abdomen with intravenous contrast
  2. B
    Endoscopic retrograde cholangiopancreatography
  3. C
    Magnetic resonance cholangiopancreatography
  4. D
    Plain radiography of the abdomen
  5. Right upper quadrant ultrasonographyAnswer

Answer

Right upper quadrant ultrasonography is the most appropriate initial imaging study to evaluate for a biliary etiology.
Right upper quadrant ultrasonography is the most appropriate initial imaging study. This patient meets the diagnostic criteria for acute pancreatitis (typical epigastric pain radiating to the back and a serum lipase >3 times the upper limit of normal). Therefore, diagnostic imaging to confirm pancreatic inflammation is not required. However, because gallstones are a leading cause of acute pancreatitis and her elevated ALT strongly suggests a biliary etiology, an ultrasound must be performed to evaluate for cholelithiasis and potential biliary ductal dilation.

Step-by-Step Solution

1
Evaluate the clinical presentation and laboratory results.
The patient has severe epigastric pain radiating to the back and a markedly elevated lipase level (3,200 U/L), which meets 2 of the 3 criteria for acute pancreatitis.
To establish the primary clinical diagnosis before determining the need for and type of imaging.
2
Determine the role of imaging in this specific scenario.
Imaging is not needed to confirm the diagnosis of pancreatitis, but rather to determine its underlying etiology.
Guidelines advise against early advanced imaging (like CT) in uncomplicated acute pancreatitis when the diagnosis is already biochemically apparent.
3
Identify the most likely etiology based on the available data.
The elevated ALT level (>150 U/L) in a patient without heavy alcohol use is highly specific for a biliary etiology (gallstone pancreatitis).
Liver function tests provide critical clues to the underlying cause of pancreatic inflammation.
4
Select the appropriate imaging modality to evaluate the suspected etiology.
Right upper quadrant ultrasonography is selected as the best initial test.
Ultrasound is the most sensitive, non-invasive, and cost-effective initial modality for identifying cholelithiasis and choledocholithiasis.

Key Concept

In patients with typical clinical and laboratory findings of acute pancreatitis, early CT imaging is unnecessary. Initial imaging should consist of a right upper quadrant ultrasound to assess for a biliary etiology.
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Ordering Imaging Studies

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