Acute Biliary Disease
Abstract & Commentary
Synopsis: In comparison to CT, initial US is superior in patients suspected of acute biliary disease.
Source: Harvey RT, Miller WT Jr. Acute biliary disease: Initial CT and follow-up US versus initial US and follow-up CT. Radiology 1999;213:831-836.
In patients with acute right upper quadrant pain and suspected acute biliary disease, cross-sectional imaging is often done in an effort to determine the precise etiology for the patient’s symptoms. Given a choice of computed tomography (CT), ultrasonography (US), or magnetic resonance (MR) imaging, is there a preferred initial examination? To address this question, Harvey and Miller did a retrospective analysis of 123 patients with clinically suspected acute biliary disease who underwent both CT of the abdomen and US of the right upper quadrant within 48 hours of one another. MR was excluded as it was considered an evolving technology, and one that is not currently cost effective for initial evaluation.
Following administration of oral and intravenous contrast, helical CT was done with 5 mm collimation and a pitch of 1.5:1.0 through the pancreas and liver. Gray-scale US was done by either a sonologist or a technologist (with immediate directed re-examination by a sonologist) using state-of-the-art 2.0 to 4.0 MHz curved array transducers. Consideration was given to the presence of gallbladder distention, biliary sludge, cholelithiasis, gallbladder wall thickening, pericholecystic fluid, choledocholithiasis, and intra- and extrahepatic biliary dilatation.
CT was done initially in 57 patients and this approach resulted in either under- or misdiagnosis in eight of 11 patients who were subsequently shown to have acute biliary disease. Follow-up US of this group suggested the appropriate diagnosis and altered clinical management in seven of these eight patients. US was done initially in 66 patients and this approach suggested either possible or acute disease in each of seven patients subsequently proven to have acute biliary disease. There were no under- or misdiagnoses, and in no case did follow-up CT alter management of this group of patients.
Considering all patients with clinically suspected acute biliary disease, comparative statistical results reported in this study revealed the following: CT sensitivity of 39% vs. US sensitivity of 83%; CT specificity of 93% vs. US specificity of 95%; CT positive predictive value of 50% vs. US positive predictive value of 75%; CT negative predictive value of 89% vs. US negative predictive value of 97%.
Comment by Faye C. Laing, MD
The major strength of this study is that it confirms US’s role as the preferred screening modality for evaluating patients with suspected acute biliary disease. When compared to CT, the primary advantage of US is its ability to detect cholelithiasis. Since CT detection of gallstones is highly dependent upon both their size and chemical composition, many stones are overlooked because their CT attenuation numbers are similar to bile. In contrast, US’s ability to detect cholelithiasis is reported as close to 100%. Other comparative advantages of US include its portability, lack of radiation, and the fact that it does not require administration of contrast material.
Somewhat surprising is that the sonographic Murphy’s sign was not used in this study for diagnosing acute cholecystitis, because in my experience when this sign is positive, it helps to distinguish patients with incidental gallstones from those with acute cholecystitis. Harvey and Miller explain that due to the retrospective nature of their study, and the fact that the Murphy’s sign result is not routinely recorded on the radiologic report, this important but subjective observation had to be omitted.
Choledocholithiasis was not visible by either modality in three patients in whom the correct diagnosis was established subsequently by endoscopic retrograde cholangiopancreatography (ERCP). In an acutely symptomatic patient, Harvey and Miller used bile duct dilatation instead (appreciated by both modalities) as a secondary finding to suggest choledocholithiasis. Despite the limited number of cases, the fact remains that once a stone leaves the gallbladder, invasive imaging is often required for its detection.
As emphasized by Harvey and Miller, important "take-away" messages are: 1) the sensitivity of US far exceeds that of CT for identifying acute biliary disease; 2) once US establishes that acute biliary disease is present, follow-up CT is unnecessary; 3) initial CT should be reserved for patients with wider diagnostic considerations or unusual symptoms; 4) when choledocholithiasis is suspected on US examination, patients should be referred for follow-up ERCP, as opposed to CT.
With respect to detecting acute biliary disease, the results of this study suggest:
a. ultrasonography is about as sensitive as computed tomography.
b. ultrasonography is much less sensitive than computed tomography.
c. ultrasound is much more sensitive than computed tomography.
d. neither computed tomography nor ultrasonography is sensitive.
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