Introduction

Hepatobiliary disease is a common cause of abdominal pain in patients evaluated in the emergency department. Cholelithiasis is present in 20 to 25 million of Americans, which represents 10% to 15% of the adult population.¹ Cholecystectomy has become the most common elective abdominal surgery performed in the United States.² Significant clinical symptoms, however, do not develop in the majority of patients (up to 80%) with gallstones.³ Both the prevalence and the complication rate of cholelithiasis increase with age. Biliary infection is a common cause of abdominal sepsis in the elderly.

Ultrasound is the initial imaging modality most commonly used for hepatobiliary evaluation in cases of suspected cholecystitis and biliary obstruction. Timely comprehensive sonographic evaluation is not always available in the emergency setting, and an increasing number of emergency providers use point-of-care biliary sonography to rapidly evaluate symptomatic patients for the presence of cholelithiasis and its complications.

Evaluation of elderly patients with suspected biliary sepsis is frequently complicated by altered mental status. In contrast to younger patients, sepsis from ascending cholangitis may be accompanied by atypical or vague clinical findings. Focused ultrasound is a valuable tool that can quickly evaluate the hepatobiliary tract and expedite appropriate treatment and disposition when signs of biliary infection are found.

Bedside ultrasound is also a useful adjunct to the emergency physician for certain patients with chronic hepatic disease. Ultrasound can quickly evaluate for the presence of ascites and provide procedural guidance for paracentesis.

Review of Literature on Evaluation for Cholecystitis

Clinical findings and laboratory data lack acceptable sensitivity to rule out cholecystitis,⁴ which has led to the need for abdominal imaging to aid in determining the patient’s disposition. Commonly used imaging modalities to evaluate for cholecystitis and its complications are ultrasound, computed tomography (CT), and cholescintigraphy or hepatobiliary iminodiacetic acid (HIDA) scanning. The sensitivity and specificity of ultrasound for the detection of cholelithiasis can approach 100% for providers with significant ultrasound experience.⁵ CT is much less sensitive than ultrasound for detecting cholelithiasis and misses up to 25% of gallstones.⁶ HIDA scanning has been reported to have high sensitivity for acute cholecystitis, but it does not provide an adequate structural evaluation of the hepatobiliary system. HIDA scanning also has limited availability in many locations and is not a practical screening modality in the emergency department setting. These distinctions make ultrasound the imaging modality of choice for the initial evaluation of patients with right upper quadrant pain and suspected cholecystitis.⁷

Emergency physicians have demonstrated the ability to effectively learn to perform point-of-care bedside hepatobiliary ultrasonography.⁸ Studies on emergency physician–performed biliary sonography have demonstrated sensitivities and specificities of up to 92% and 87% for the detection of cholelithiasis.^9,10

Biliary Duct Evaluation

Transabdominal ultrasound is the initial imaging modality used to evaluate for suspected choledocholithiasis and obstruction of the biliary ducts. In the western world, gallstones are the most common cause of both biliary obstruction and cholangitis.^11,12 Even with the most advanced equipment, the sensitivity of ultrasound in detecting choledocholithiasis is still essentially dependent on the examiner’s proficiency and can range between 22% and 100%.^5,11,13–15 Specific data on the accuracy of emergency medicine physicians’ performance in detecting choledocholithiasis are not yet available and need further investigation. The overall specificity of transabdominal sonography for detection of common bile duct (CBD) stones is usually very high and ranges between 95% and 100%.¹¹

Biliary Sepsis

In patients older than 65 years, cholecystitis and cholangitis each account for 12% of the causes of intraabdominal sepsis, or 24% of the total causes of intraabdominal sepsis combined.¹⁶ Bedside ultrasound can be used to detect this common entity and expedite the initiation of appropriate antibiotics and consultation if signs of biliary infection or obstruction are identified.

How to Scan, Probe Selection, and Machine Settings

Bedside hepatobiliary imaging is most often performed with a lower-frequency (2- to 5-MHz) curvilinear probe (Fig. 45.1). The lower frequencies typically provide the most appropriate penetration relative to the depth of the structures of interest. In young or very thin patients with superficially located structures of interest, use of a higher-frequency probe may provide better image resolution. A phased-array probe can limit the amount of rib shadowing when intercostal imaging is required.

Fig. 45.1 Position for initial placement of the transducer.

The probe is placed below the subcostal margin (blue line) at the intersection with a line running from the right shoulder to the umbilicus (black arrows) and angled at about 45 degrees. The probe marker points to the right of the patient (white arrow).

After selecting the abdominal preset, the gain should be adjusted accordingly. The depth needs to be optimized to see the structures of interest and the area posterior to them without creating needless dead space beyond them. Tissue harmonic imaging has been demonstrated to enhance the visibility of lesions and diagnostic confidence in abdominal imaging, particularly in areas containing echogenic tissue such as fat, calcium, or air.¹⁷ The tissue harmonics feature should be used when assessing the gallbladder because it typically reduces artifact interference and facilitates imaging. The sonographer should also be comfortable with the color and power Doppler functions, which can be used to distinguish the biliary ducts and gallbladder from adjacent vascular structures.

Patient Positioning

Imaging begins with the patient in a supine position, but it should be acknowledged that repositioning the patient is required in many cases to obtain the views needed. Rolling the patient to the left lateral decubitus position can help displace the bowel and reduce interference from bowel gas. In some cases, rolling a patient to a semiprone position or having the patient stand up may further facilitate image acquisition. If possible, the patient should elevate the right arm above the head to improve the sonographic accessibility of the inferior liver and for transthoracic scanning.

Inspiratory Techniques

Having patients hold their breath after a full inspiration is also a useful technique. This pushes the liver inferiorly and may aid in displacing the overlying bowel. The liver also provides a friendly imaging window. However, breath-holding can increase air in the antrum, pylorus, and duodenum, which can interfere with the ability to visualize the gallbladder. In general, in the beginning of the examination it is often better to place the probe over the anatomic area of interest and review structures of interest as they are pushed in and out of the sonographic field via the normal respiratory cycle. Once the patient initiates breath-holding, air swallowed into the antrum will quickly move with peristalsis and may obscure areas of interest.

Systematic Scanning Approach

Significant anatomic variability, interference from adjacent bowel, and variations in the amount or overlying tissue can make localization of the gallbladder a difficult task. Gallbladder imaging is best approached as a dynamic process, and the sonographer should be prepared to try different imaging windows and repositioning of the patient as needed to obtain the appropriate images.

The authors suggest the following systematic approach:

Fig. 45.2 The probe is placed in the next intercostal margin (blue lines) at the intersection with the right shoulder–umbilicus axis (black arrows) and angled perpendicularly or slightly caudally. The probe marker points to the right of the patient (white arrow).

Gallbladder Evaluation

After locating the gallbladder, the probe is rotated clockwise and counterclockwise as needed to obtain a longitudinal (long-axis) view (Fig. 45.3). Next, the probe is moved medially and laterally to evaluate the entire gallbladder in long axis. A normal gallbladder has echogenic walls with an anechoic internal cavity. The gallbladder should be thoroughly evaluated for the presence or absence of cholelithiasis. Special attention should be paid to the gallbladder neck for impacted stones.

Fig. 45.3 Image of the gallbladder in transverse (A) and longitudinal (B) views.

Following long-axis evaluation, the probe is rotated 90 degrees to the patient’s right (the indicator is rotated 90 degrees counterclockwise), which will give a transverse or short-axis view of the gallbladder (see Fig. 45.3). The probe should be angled or moved cephalad and caudad to evaluate the entire gallbladder. The gallbladder is scanned from the fundus to the neck. Again, particular attention should be directed to the gallbladder neck. Air artifact can obscure small stones in this area.

The next step should be to measure the thickness of the gallbladder wall (Fig. 45.4). Transmission of ultrasound waves through the fluid-filled gallbladder leads to enhancement of the posterior gallbladder wall, and posterior enhancement can result in overestimation of wall thickness. Hence, measurements are obtained at the anterior wall. Thickness of the anterior wall greater than 3 mm is considered abnormal.¹⁸ One should be aware that isolated increased gallbladder wall thickness is not a sensitive finding for detecting acute inflammation because it can be caused by multiple disease processes (e.g., chronic cholecystitis, ascites, hepatitis).¹⁹ Next, the area encompassing the gallbladder should be evaluated for the presence of pericholecystic fluid. This finding will appear as anechoic areas adjacent to the gallbladder. Pericholecystic fluid with septations, internal echoes, or thick walls may suggest perforation of the gallbladder with abscess formation.¹⁸

Fig. 45.4 Measuring gallbladder wall thickness.

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