Gallstone disease ultrasound
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hadeel Maksoud M.D.[2]
Overview
Generally transabdominal ultrasound (TAUS) is considered to be the most useful test to detect gallstones. TAUS is noninvasive, readily available, relatively inexpensive and doesn't expose patients to ionizing radiation. The patient should fast for at least eight hours before the examination this is to ensure that the gallbladder is distended with bile, which is best for visualizing stones.
Transabdominal ultrasound
Ultrasound may be helpful in the diagnosis of gallstones. Findings on an ultrasound suggestive of gallstones include:
- Gallstones - echogenic foci that cast an acoustic shadow
- Gravel - multiple, small echogenic foci and cast shadows
- Sludge - microlithiasis that is echogenic but doesn't cast a shadow[1]
False-negative or misleading results may be obtained if the gallbladder is completely filled with stones or if it is contracted around many stones.[2]
Test characteristics — Multiple studies have evaluated the ability of transabdominal ultrasound to detect gallstones, though it is important to recognize that precise estimates of sensitivity and specificity are difficult to determine since surgical confirmation of a negative sonogram is unlikely.
A systematic review estimated that the sensitivity was 84 percent (95% confidence interval [CI] 76 to 99%) and specificity was 99 percent (95% CI 97 to 100%) [33]. Rarely, advanced scarring and contraction of the gallbladder around gallstones leads to nonvisualization of the gallbladder lumen, which has a specificity of 96 percent, but it should also raise the possibility of gallbladder cancer.
When compared with other cross-sectional imaging modalities and cholecystography, ultrasound has the highest sensitivity [34,35]. Modern sonographic equipment is able to detect stones as small as 1.5 to 2 mm in diameter [34]. Smaller stones may be missed, and the sensitivity falls to 50 to 60 percent for stones less than 3 mm in diameter [36-38].
The accuracy of transabdominal ultrasonography is operator-dependent. The entire gallbladder must be examined axially and sagittally. Every effort should be made to examine the outlet of the gallbladder (Hartmann's pouch), where gallstones may be difficult to detect. The gallbladder neck must be traced all the way into the porta hepatis to exclude stones in this region. If an out-pouching from the gallbladder (Phrygian cap) is present, the redundant portion of the fundus must not be overlooked.
Even with an experienced operator, it is difficult to determine the number or size of stones in the gallbladder with transabdominal ultrasound. This is especially true for very small stones (1 or 2 mm in diameter) that frequently, when present in large numbers, can appear on transabdominal ultrasound as one large stone.
In patients with typical biliary colic but no gallstones on ultrasonography, we usually repeat the transabdominal ultrasound in a few weeks. If the repeat transabdominal ultrasound is negative, the patient may have microlithiasis or may be a category 4 patient (typical biliary symptoms without gallstones on ultrasound). In such patients the next step is debatable. The approach depends on the patient's preferences, age, and risk factors for adverse outcomes with invasive procedures.
Imaging studies — Most patients with uncomplicated gallstone disease will have gallstones demonstrated on transabdominal ultrasound.
Endoscopic ultrasound — Imaging of the gallbladder can be obtained by EUS. During EUS, an ultrasound transducer on the tip of an endoscope is placed into contact with the gastric antrum, which is in close proximity to the gallbladder. This permits gallbladder visualization without interference from bowel gas, subcutaneous tissue, or the liver. As a result, EUS is more sensitive than transabdominal ultrasound for the detection of gallstones, particularly in patients who are obese or have other anatomic considerations that limit gallbladder visualization with transabdominal ultrasound [40,41].
Several studies have demonstrated that EUS is useful for the detection of small stones and microlithiasis [40-43]. In one study of 45 patients in whom there was a clinical suspicion of cholelithiasis but with at least two normal transabdominal ultrasound examinations, EUS detected evidence of cholelithiasis in 26 patients (58 percent). The sensitivity and specificity of EUS for detecting cholelithiasis were 96 and 86 percent, respectively [40].
In a second study of 89 patients with acute pancreatitis, EUS revealed small gallbladder stones (1 to 9 mm) in 14 of 18 patients who had otherwise negative standard imaging studies, including transabdominal ultrasound [41]. Subsequent endoscopic retrograde cholangiopancreatography (ERCP) and cholecystectomy confirmed the presence of stones in all 14 patients. None of the remaining four patients developed evidence of cholelithiasis during a median follow-up of 22 months.
The initial imaging study of choice in patients with suspected common bile duct stones is a transabdominal ultrasound of the right upper quadrant. Transabdominal ultrasound can evaluate for cholelithiasis, choledocholithiasis, and common bile duct dilation. It is readily available, noninvasive, permits bedside evaluation, and provides a low-cost means of evaluating the common bile duct for stones. (See "Ultrasonography of the hepatobiliary tract".)
The sensitivity of transabdominal ultrasound for choledocholithiasis ranges from 20 to 90 percent [14]. In a meta-analysis of five studies, the pooled sensitivity of ultrasound for detecting a common bile duct stone was 73 percent, with a specificity of 91 percent [20]. Transabdominal ultrasound has poor sensitivity for stones in the distal common bile duct because the distal common bile duct is often obscured by bowel gas in the imaging field [21-25]. Occasionally, a definite common bile duct stone (one that casts a shadow) can be imaged by transabdominal ultrasound (image 1).
A dilated common bile duct on transabdominal ultrasound is suggestive of, but not specific for, choledocholithiasis [6,8,10]. A cutoff of 6 mm is often used to classify a duct as being dilated [14]. However, using a cutoff of 6 mm may miss stones [26]. One study of 870 patients undergoing cholecystectomy found that stones were often detected in patients whose ducts would have been classified as "nondilated" using the 6 mm cutoff [27]. In addition, the probability of a stone in the common bile duct increased with increasing common bile duct diameter:
●0 to 4 mm: 3.9 percent ●4.1 to 6 mm: 9.4 percent ●6.1 to 8 mm: 28 percent ●8.1 to 10 mm: 32 percent ●>10 mm: 50 percent Conversely, because the diameter of the common bile duct increases with age, older adults may have a nolder adults may have a normal duct with a diameter that is >6 mm. (See "Ultrasonography of the hepatobiliary tract", section on 'Normal measurements on ultrasound'.)
References
- ↑ Conrad MR, Janes JO, Dietchy J (1979). "Significance of low level echoes within the gallbladder". AJR Am J Roentgenol. 132 (6): 967–72. doi:10.2214/ajr.132.6.967. PMID 108978.
- ↑ Leopold GR, Amberg J, Gosink BB, Mittelstaedt C (1976). "Gray scale ultrasonic cholecystography: a comparison with conventional radiographic techniques". Radiology. 121 (2): 445–8. doi:10.1148/121.2.445. PMID 981625.
- ↑ "Gallstones | Radiology Reference Article | Radiopaedia.org".