Bedside Ultrasonography for Gallbladder Disease

Hepatobiliary disease is a common problem in patients presenting to emergency departments or primary care settings. Because clinical examinations and laboratory evaluations do not have by themselves adequate sensitivity and specificity to accurately diagnose many of these entities, the evaluation for gallstone or gallbladder-related disease includes ultrasonography. Point-of-care bedside ultrasound has been shown to be a viable imaging modality for the diagnosis of gallstones and gallbladder-related diseases. ^[1]  Focused bedside ultrasonography (BUS) is an increasingly available and helpful diagnostic tool that can further evaluate patients with suspected biliary disease. ^[2] In one study, test characteristics of emergency physician bedside ultrasonography were similar to those of radiology-performed ultrasonography for detection of cholecystitis. ^{[3, 4]} Bedside ultrasonography for gallbladder disease is also a skill that can be learned by physicians at all levels of training. ^{[5, 6, 7]}

The benefits of focused bedside biliary sonography include the following:

• Decreases the time to diagnosis for cholelithiasis and cholecystitis. ^[8]

• Helps accurately diagnose biliary pathology, ^{[8, 9]}  with a sensitivity of 90-96%, specificty of 88-96%, positive predictive value of 88-99%, and negative predictive value of 73-96%. ^[10]

• Helps assess the degree of obstruction in choledocholithiasis.

• Can help diagnose gallstones definitively, which makes alternative diagnoses less likely. ^[11]

• Can be performed rapidly at the bedside.

• Can provide bedside radiographic corroboration of physical examination findings for the treating physician.

• Does not involve ionizing radiation and, as such, is safe in pregnant patients and children. ^[12]

Necessary equipment includes the following:

• Ultrasound machine with color flow Doppler.

• Low-frequency (2-5 MHz) curvilinear or phased array transducer.

• Acoustic coupling gel.

• Appropriate materials to drape the patient.

Patients should be evaluated in the supine position but can be positioned in the upright, standing, or left lateral decubitus position for improved visualization. Male patients should have their entire right hemithorax exposed for examination. Take care particularly with female patients to drape appropriately and to minimize exposure of sensitive areas.

Contrast-enhanced ultrasound is a minimally invasive diagnostic technique that is useful in visualizing not only the shape of cancer lesions and some areas of direct invasion to the liver, but also metastasis. ^{[13, 14]}

Anesthesia generally is not necessary for abdominal sonography; however, pain management should not be delayed, and patients may experience some discomfort due to probe pressure. For improved patient comfort, consider using warmed ultrasound conducting gel, if available.

When emergent treatments such as intravenous fluids, antibiotics, or pressors are indicated, performance of abdominal sonography should not delay initiation of these treatments. Ongoing resuscitation and extremis, however, are not contraindications. Although challenging to perform in such situations, bedside biliary sonography can be easily incorporated into the flow of patient care.

Bedside ultrasound is accurate for the detection of gallstones, but the imaging diagnosis of acute cholecystitis is more challenging. This suggests that BUS has the potential to improve efficiency of surgical assessment in suspected acute gallstone disease and supports the ongoing provision of BUS in surgical services. ^[15]

Hemorrhagic cholecystitis, a rare complication of acute cholecystitis, is a potentially fatal diagnosis. This disorder may be difficult to detect because symptoms are similar to more common diagnoses. BUS is a useful imaging technique in the emergency setting, where it is readily available to enable immediate interpretation and application of results to guide medical decision making. BUS used by emergency medicine providers can facilitate the rapid recognition and treatment of specific, life-threatening hepatobiliary pathology while excluding alternative diagnoses. ^[16]

Positive findings of gallstones and increased gallbladder wall thickness are highly predictive of the need for surgical intervention, and BUS is associated with shorter emergency department stays. ^[17]

Patients who present with a history and physical exam consistent with biliary disease should undergo a focused bedside biliary sonography. Such signs and symptoms include the following:

• Abdominal pain associated with ingestion of food

• Colicky right upper quadrant or epigastric abdominal pain

• Jaundice

• Atypical right-sided chest or shoulder pain

• Abnormal liver function laboratory studies

The American College of Emergency Physicians (ACEP) Policy Statement indicates that focused bedside biliary sonography should include the following ^[18] :

• Primary: identification of cholelithiasis
• Extended: cholecystitis; common bile duct abnormalities, including dilation and choledocholithiaisis; liver abnormalities, including tumors, abscesses, intrahepatic cholestasis, pneumobilia, hepatomegaly; portal vein abnormalities; other gallbladder abnormalities, including tumors, unexplained jaundice, Ascites

When findings leading to concern for hepatic malignancy are found incidentally on BUS, care must be taken to instruct the patient regarding further follow-up. Patients will need further imaging (ie, computed tomography scan) and work-up.

Relevant anatomy

The gallbladder is superior and anterior to the right kidney. It typically lies between right and quadrate lobes of the liver in a slightly oblique position. Landmarks for the gallbladder are the undivided right portal vein and the main lobar fissure. The main lobar fissure is a bright, hyperechoic line that extends from the right portal vein to the gallbladder fossa. The main lobar fissure is the functional division of the liver (divides right and left lobes) and is seen in most patients; however, it may be short or absent in some patients. The gallbladder neck tapers into the cystic duct. The common bile duct (CBD) travels anterior to the portal vein and right of the hepatic artery. (See the moving image below.)

Components of examination

Key components of the biliary ultrasound include the following ^[18] :

• Transverse and longitudinal views of the gallbladder with clear anatomic relationship to the liver, kidney, and portal vein for unambiguous identification

• Gallbladder wall thickness

• Presence or absence of gallstones

• Presence or absence of biliary sludge

• Presence or absence of pericholecystic fluid

• Diameter of the common bile duct

• Presence or absence of the sonographic Murphy sign

The examination can be technically limited by obese habitus, bowel gas, and/or abdominal tenderness. ^[18]

Technique

With the patient in the supine position, place the probe in the right upper quadrant.

Once the gallbladder is clearly identified, obtain longitudinal and transverse views of the gallbladder. (See the images below.)

If stones are seen, obtain a dependent view (upright, standing, or left lateral decubitus) to assess the mobility of the stones. (See the images below.)

Use the liver as an acoustic window. If the gallbladder cannot be visualized (because of bowel gas or a more lateral or cephalad location of the gallbladder), try moving laterally or superiorly. Moving the probe cephalad may necessitate scanning through or between the right lower ribs; in such cases, consider switching to a phased array probe, which has a smaller footprint and is easier to position between the ribs. (See the image below.)

The video below depicts a demonstration of biliary evaluation.

Ultrasonographic criteria

Most gallstones produce acoustic shadows. (See the image below.)

Gallstones typically demonstrate gravitational dependency and mobility. (See the image below.)

Cholesterol stones and stones smaller than 1 mm may not produce prominent shadows; they may instead result in a hazy appearance posteriorly. Nonshadowing, nonmobile, round-appearing masses can be polyps.

Sludge is less echogenic than stones, does not shadow, forms a fluid level, and moves slowly as compared to stones.

Findings that suggest acute cholecystitis include gallbladder wall thickening (>4 mm), double wall sign, pericholecystic fluid, or a sonographic Murphy sign (pain elicited by pressing the ultrasound probe over the fundus of the gallbladder). ^[19]  (See the image below.)

Gallbladder wall thickening may be seen in nonbiliary pathologic states such as the postprandial state, hypoproteinemia, chronic liver disease (hepatitis, cirrhosis), pancreatitis, HIV infection, and congestive heart failure. ^{[18, 20]}  (See the image below.)

Common bile duct diameters range from 4 to 10 mm, depending on the patient’s age (normal is 3-4 mm; add 1 mm for every 10 years after age 40 years). Patients who are status post cholecystectomy can have common bile ducts up to 10 mm in size. A dilated common bile duct can suggest choledocholithiasis, cholecystitis, or biliary obstruction. ^[21]  In a study of ultrasound measurements of the bile ducts and gallbladder, the gallbladder wall was found to be thicker in patients with gallstones (+0.4 ± 1.4 mm; P=0.0049), sludge (+0.5 ± 1.4 mm; P=0.0019), and acute cholecystitis (+3.1 ± 1.6 mm; P< 0.0001). With biliary obstruction, the extrahepatic bile duct, right duct, left duct, and gallbladder volume measurements were 6.0 ± 2.1 mm, 4.2 ± 1.4 mm, 4.1 ± 1.4 mm, and 171 ± 207 mL, respectively (P< 0.0001 for all values). ^[21]  (See the image below.)

(The moving image below depicts cholecystitis.)

Causes of false-positive and false-negative studies are as follows ^{[18, 22]} :

• Small gallstones: overlooked or mistaken for gas in the adjacent loop of bowel

• Gas in the loops of bowel adjacent to the posterior wall of the gallbladder

• Small stones in the gallbladder neck

• Polyps mistaken for gallstones

• Mistaking the gallbladder for other fluid-filled structures, including portal vein, inferior vena cava, and hepatic or renal cysts

• Failure to identify the gallbladder may occur with chronic cholecystitis, particularly when filled with stones

If the gallbladder is difficult to visualize, consider repositioning the patient into an upright, standing, or left lateral decubitus position. Asking the patient to take and hold a deep breath results in downward excursion of the diaphragm and may bring the gallbladder down and out from beneath the costal margin.

If the patient is very thin or has an anterior gallbladder, consider increasing the frequency to 5 MHz.

Although rare, in chronic congenital conditions such as Caroli syndrome, biliary duct dilatation can observed.

Emphysematous cholecystitis (EC) is a form of cholecystitis with high mortality rates more commonly seen in patients with medical histories such as diabetes, hypertension, and peripheral vascular disease. Common features of these medical diseases include impaired pain perception, particularly abdominal pain, due to advanced age and peripheral neuropathies. Accurate evaluation of characteristics observed on ultrasonography is therefore highly important for these patients. The champagne detected while the hepatobiliary system is evaluated on BUS is a valuable finding in the diagnosis of EC with high mortality. ^[23]

A clinical prediction score for cholecystitis shows accuracy equivalent to Tokyo Guidelines (TG)13. Use of this score may streamline work-up by decreasing the need for comprehensive ultrasound evaluation and C-reactive protein measurement and may shorten patient stay in the emergency department. ^[24]

Nonshadowing, nonmobile, round-appearing masses can be polyps. Patients with indeterminate or suspicious masses should receive further imaging and work-up. Consider obtaining a comprehensive ultrasonographic examination and having the patient follow up with his or her primary care provider.

Many patients with biliary cancer also have gallstones and can develop a calcified gallbladder wall with focal thickening. ^[25] Calcified gallbladders, also known as porcelain gallbladders, have a high frequency (up to 22%) of association with adenocarcinoma. In patients with calcified gallbladders or with suspected biliary cancer, further imaging and work-up are indicated.

If gallbladder cysts or masses are identified, patients should undergo further imaging and work-up. Consider obtaining a comprehensive ultrasonographic examination and having the patient follow up with his or her primary care provider.

Mucosal folds (ie, junctional fold or Phrygian cap) within the gallbladder are common. Caution must be applied to not misinterpret them as septae, polyps, or stones.

Ultrasonography can reduce the use of computed tomography for diagnosis of appendicitis; however, negative scan results do not rule out disease. BUS can accurately diagnose and rule out gallbladder pathology and is effective for diagnosing urolithiasis. ^[26]

Acute gallstone disease—primarily biliary colic and acute cholecystitis—represents a significant burden on surgical services. Prolonged waiting times for ultrasonography to confirm the diagnosis contributes to inefficiency and delays surgery. BUS offers clinicians the opportunity to make the diagnosis more promptly and streamline acute surgery. ^[15]

Choledocholithiasis complicates approximately 10% of gallstone disease and often requires admission and invasive testing. Using BUS in conjunction with liver function tests and patient assessments may obviate the need for endoscopic retrograde cholangiopancreatography. ^[27]

Common pitfalls include the following:

• Failing to visualize the entire gallbladder, resulting in missed gallstones—in particular, stones in the neck of the gallbladder

• Misinterpreting artifacts (side lobe artifact, edge artifact) as pathology

• Misinterpreting scattering from adjacent small bowel as acoustic shadowing

• Attempting to interpret inadequate or technically limited studies