Does Computed Tomography (CT) Overestimate Common-Bile-Duct Diameter in the Evaluation of Gallstone Pancreatitis?

Background Acute pancreatitis is a common reason for inpatient admissions in the United States with around 300,000 admissions annually. Gallstones are the most common etiology for acute pancreatitis, and may be associated with a dilated common bile duct. The diameter of the common bile duct is commonly assessed with ultrasound, computed tomography and magnetic resonance imaging. Methods A retrospective analysis of a database of patients who underwent cholecystectomy at our institution from 2000 to 2013 was performed. Patients with a diagnosis of gallstone pancreatitis were identified. A paired-samples T-test was used to compare measurements of commonbile-duct diameter by ultrasound, computed tomography, and magnetic resonance imaging. A P-value <0.05 was regarded as significant. Results Among 6,876 patients undergoing cholecystectomy, 738 (11%) were diagnosed with acute gallstone pancreatitis. Of those with acute gallstone pancreatitis, most (600; 81%) had an ultrasound documented in the medical record, while just less than half (344; 47%) had a computed tomography, and a third (217; 29%) a magnetic resonance imaging. Of the 600 who underwent a preoperative ultrasound, 281 (47%) also underwent computed tomography and 183 (30%) also underwent magnetic resonance imaging. The diameter of common bile duct was significantly larger by computed tomography compared to ultrasound (11.2 vs. 8.7, P=0.022) in patients imaged with both modalities. Common-bile-duct diameter was similar by magnetic resonance imaging and ultrasound (7.0 vs. 7.1, respectively, P=0.859), and by magnetic resonance imaging and computed tomography (10.5 vs. 13.9, respectively, P=0.059). Conclusion Computed tomography scan may overestimate the diameter of the common bile duct compared to magnetic resonance imaging and ultrasound in the setting of acute gallstone pancreatitis, and should therefore be interpreted with caution. Received October 1st, 2015 Accepted November 19th, 2015