J. Christian Fox, M.D., RDMS, William P. Scruggs, M.D., RDMS
I. Introduction and Indications
Gallbladder disease affects 8 % of men and 17 % of women in the United
States resulting in over 600,000 surgeries each year.(1,2) Cholecystitis,
the most common emergent surgical condition of the gallbladder, is diagnosed
in up to 10 % of total patients and 21 % of elderly patients presenting
to the emergency department with acute abdominal pain.(3-5) Overall,
biliary tract disease is the 3rd most common cause of acute abdominal pain
presenting to the emergency department. The associated annual costs
total $5.8 billion and result in more than 5000 deaths a year.(6,7)
In the acute presentation of biliary tract disease, the priority is to
discriminate between biliary pain (also called biliary colic) and more
serious diseases such as acute cholecystitis that require hospital admission,
intravenous antibiotic therapy, and possibly emergent surgery. Unfortunately,
no combination of clinical symptoms, signs, and laboratory values can reliably
make that differentiation. Classically, patients with symptomatic biliary
disease present with severe, steady pain in the epigastrium or right upper
quadrant and may radiate to the right scapular region.(8,9) Dyspeptic
symptoms such as nausea, vomiting, bloating, belching, acid regurgitation,
and heartburn are not uncommon but do not add to the diagnostic certainty.(10,11) Self-resolving
biliary pain generally lasts 15-minutes to 5-hours, but may persist up
to 24 hours. Right upper quadrant tenderness is typically present
on physical examination in both biliary pain and cholecystitis. Murphy’s
sign, the arrest of inspiration on deep palpation of the right upper quadrant,
is present in 90% of patients with acute cholecystitis. Fever and
leukocytosis are common, but the combination of both does not occur in
one-third of patients with cholecystitis.(12)
Due to the difficulty in confirming the appropriate diagnosis on clinical
grounds, imaging is used in most cases. Ultrasound is the initial
imaging study for the diagnosis of acute cholecystitis because it is performed
relatively quickly and does not expose the patient to radiation.(13) Adjusting
for verification bias, sensitivity is 88 % and specificity is 80 %.(14) Ultrasound
does not expose the patient to radiation and is much more accurate than
plain film radiographs or computed tomography. Furthermore, the modality
is faster and more generally more readily available than cholescintigraphy
or MRI.
It is important to note, however, that ultrasound is not the most accurate
imaging modality for the diagnosis of acute cholecystitis. Cholescintigraphy,
usually in the form of the HIDA scan, is 97 % sensitive and 90 % specific
(after adjusting for verification bias).(14) Radionucleotide
material is injected intravenously and is excreted through the bile. A
nuclear study is then performed to evaluate the filling of the gallbladder. If
the cystic duct is obstructed, as in the case of acute cholecystitis, the
gallbladder will not fill and the test is considered positive. Cholescintigraphy
should be considered in patients with a high clinical suspicion and a negative
ultrasound.
II. Anatomy
The gallbladder is an elongated, pear shaped organ that functions to concentrate
and store bile. Along with the liver, it is an embryologic derivative
of the foregut. It normally lies on the visceral surface of the liver
between the quadrate and right hepatic lobes covered by a continuation
of the hepatic peritoneum.
The gallbladder consists of the fundus, body, and neck. The fundus
is the most caudal portion of the gallbladder and often will protrude from
under the inferior margin of the liver and contact the anterior wall of
the abdomen. The
body of the gallbladder tapers cranially, eventually becoming the neck
of the gallbladder, which continues to narrow to the junction with the
cystic duct. At
its neck, the gallbladder makes a sharp turn away from the parenchyma of
the liver into the peritoneal cavity where it becomes the cystic duct.
The cystic duct carries bile to and from the gallbladder and common bile
duct into the duodenum. It is up to 5 cm long, and it joins the common
hepatic duct to create the common bile duct (CBD). The CBD courses
along the free border of the lesser omentum along with the hepatic artery
and the portal vein. It passes behind the duodenum and into the head
of the pancreas where it meets the ampulla of Vater at the duodenal papilla. The
sphincter of Oddi functions at the ampulla to inhibit the flow of biliary
and pancreatic secretions into the duodenum, until it is relaxed by cholecystokinin
in response to the ingestion of food.
.jpg)
Illustration
1a: Anatomical overview of upper abdomen.
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Illustration 1b: Overview of porta hepatis.
Bile is produced by hepatocytes and passes down through the biliary ducts
of the liver. When the ampulla of Vater is open, bile flows freely
into the duodenum. When closed, bile backs up into the cystic duct
and into the gallbladder. The smooth muscle of the gallbladder aids
flow toward the duodenum by contracting with stimulation by cholecystokinin.
Within the abdominal cavity, the gallbladder most commonly lies anterior
to the first and second portion of the duodenum, hepatic flexure, and stomach.
Variations in gallbladder shape are common. Folds within the body
of the gallbladder occur frequently. Septations and duplication of
the gallbladder are rare and make diagnoses in pathologic conditions difficult.
III. Scanning Technique and Normal Findings
Gallbladder: Curvilinear abdominal
probes with a frequency ranging from 2-5 MHz are ideal for examination
of the gallbladder. The lower end of this range
may be necessary for sufficient penetration in larger patients. However,
sonographers should increase the frequency whenever possible as the evaluation
of wall thickness, pericholecystic fluid, and gallstones is significantly
improved with better resolution.
The gallbladder is identified with three basic approaches: The “subscostal
sweep” , the “X minus 7” and the "flattening
the probe" approach. The
subcostal sweep is generally the most effective window and is usually attempted
first. Start
the scan with the probe in longitudinal orientation and the probe-indicator
oriented toward the patient’s head and instruct the patient to take
a deep breath. Sweep the probe inferiorly and laterally along the
subcostal margin (Video 1).
Video clip 1: Subcostal
sweep video (includes audio).
The X-Minus 7 approach is an intercostal window. Find the xiphoid process and move laterally to the right approximately 7 centimeter. Place the probe perpendicular to the skin between the ribs. In most cases, the gallbladder will be found posterior to the liver parenchyma immediately beneath the probe. In the few instances where the gallbladder is not identified, move the probe laterally, sweeping through the liver (Video 2).
Video clip 2: Video
clip showing the “X-minus
7” approach (includes audio).
In many young patients in a supine position, the gallbladder will be very anterior and cranial. In these cases, it is often helpful to point the indicator toward the patient’s right and flatten the probe against the abdomen while aiming the beam toward the right shoulder. Fan the beam anterior to posterior to identify the gallbladder (Video 3).
Video clip 3: Video
clip showing the “Flattening
the probe” technique (includes audio).
With any of the three views, once the gallbladder is identified, stop moving the probe and make small adjustments to create the best long-axis view. In the long-axis, the gallbladder will usually appear as a pear-shaped, hypoechoic structure with a hyperechoic wall.
Video clip 4: Gallbladder
long axis: Note the main hepatic fissure extending from the tapered end
of the gallbladder to the cross-section of the portal vein. The entire complex resembles an exclamation point.
Because the gallbladder sits in the fossa created by the right and left
main lobes of the liver, the main hepatic fissure appears as an echogenic
line that extends from the neck of the gallbladder to the portal vein and
serves as a landmark. The complex of the gallbladder, main hepatic
fissure, and portal vein (in the short-axis) has the appearance of an exclamation
point (Video 4). Fan the ultrasound beam through the entirety of
the gallbladder to identify any pathology.
As with any organ of the body, the gallbladder should be viewed in two
planes. After the long-axis is thoroughly examined, pivot the probe
90 degrees and demonstrate the short-axis (Video 5). In the short-axis,
the gallbladder will appear spherical. Again, scan through the entire
organ in the short axis (Video 6).
Video clip 5: Rotating the probe (includes
audio).
Video clip 6: Gallbladder
short axis: The
video demonstrates fanning through the short axis of the gallbladder from
the neck to the fundus.
The gold standard to evaluate the g allbladder wall thickness is evaluated from the short-axis. Measure the anterior gallbladder wall at its most narrow point. It is important to obtain a view while the probe and ultrasound beam are perpendicular to the gallbladder wall. If an oblique section of the wall is measured, the reading will be falsely elevated (Video 7).
Video clip 7: Measuring the gallbladder wall: To
properly measure the gallbladder wall, view the organ in the short-axis
and freeze the image on the narrowest portion of the wall.
Importantly, the normal gallbladder may be contracted. The lumen of the gallbladder will appear very narrow in these cases and the wall will be thickened with a characteristic three layer appearance. The inner and outer walls are echogenic while the middle layer is relatively hypoechoic (Video 8).
Video clip 8: Contracted gallbladder wall: This
image demonstrated the classic appearance of the contracted gallbladder
wall. Note the three distinct layers of the wall. The wall
is thickened, but pathologic thickening will not demonstrate the three
layers of the wall.
Video clip 9: Mickey Mouse sign: The video
shows an enlarged view of the portal triad in the short-axis. The
CBD and hepatic artery form the ears of the Mickey Mouse sign. When
power flow Doppler is added, the portal vein (large circle) and the hepatic
artery (Mickey’s left ear) demonstrate flow.
With the indicator directed toward the patient’s right, the
right ear will be the common bile duct and the left ear the hepatic artery.
The best way to evaluate the CBD is in the long axis as gallstones, strictures,
or external compression may occur at any point in the tubular structure. Maintain
the Mickey Mouse sign in the center of the screen and rotate the probe
90 degrees without changing the location of the probe on the patient’s
skin. In the long axis, three echogenic lines will stretch across
the screen. The line closest to the probe will be the anterior wall
of the common bile duct. The second line is the shared anterior wall
of the CBD and portal vein. Finally, the third line is the posterior
wall of the portal vein. If there is confusion differentiating between
the CBD and portal vein, color flow or power Doppler can be used. The
portal vein will demonstrate flow and the CBD will not (Video 10).
Video clip 10: Measuring the CBD: This
video demonstrates the porta hepatis in the long-axis with power flow
Doppler. The
CBD lies in the long-axis just anterior to the portal vein. The
Doppler is not absolutely necessary, but it is helpful as the hepatic
artery is sometimes visualized instead. This CBD is not measured
in the video, but is of normal caliber.
Video clip 11: This video shows a normal CBD. The clip has three sections: first, three important structures are demonstrated in regular B-Mode: The long, black structure closest to the bottom of the image is the inferior vena cava (IVC) coursing beneath the liver. Above that is the portal vein. The portal vein is tortuous in this video and the black circular structure at the end of the portal vein to the left is the continuance of the portal vein. Finally, above the portal vein is the narrow CBD. In the second part flow is demonstrated using power Doppler. Note the flow through the IVC and several sections of the portal vein. In the third part of the clip, magnification (Zoom function) is applied in B-Mode and the CBD is measured.
Follow the
CBD as far distally as possible by moving the probe medial in relation
to the patient. It is very difficult to follow the CBD,
as it passes posterior to the second portion of the duodenum. It
is often identified within the head of the pancreas medially. Keep
in mind that pathology other than choledocholithiasis can result in a dilated
CBD and remain suspicious for tumors in the head of the pancreas.
The CBD should be measured at its largest diameter in the long-axis. Calipers
should be used to measure from the interior margin of the anterior wall to the
interior margin of the posterior wall.
IV. Pathology
There are five major pathologic findings in the ultrasonographic diagnosis of acute cholecystitis:
1. Gallstones/Sludge: Gallstones are evident
in 90-95 % of acute cholecystitis and likely play a role in the development
of gallbladder cancers as well. They are demonstrated on ultrasound
with a thin, echogenic rim with pronounced shadowing obscuring the tissues
behind. Small gallstones may not shadow. In such cases, increasing
the frequency will improve resolution and shadowing may become apparent. Most
often, gallstones are mobile and will “roll” to the most dependant
portion of the gallbladder. This phenomenon may be demonstrated on
ultrasound by maintaining a view of the gallbladder while a patient is
rolled to a new position such as left lateral decubitus. Note the
location of the gallstones in relation to the neck of the gallbladder. Stones
in the neck of the gallbladder may be more likely to cause cholecystitis.
Gallstones come in many shapes and sizes. Some will be only a couple
of millimeters in diameter while others will grow to larger than 2 centimeters. Sometimes
only a single gallstone will be present, while other patients will have
multiple stones (Video 12-18).
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Video clip 12 |
Video clip 13 |
Video clip 14 |
Video clip 12: Large gallstone: The video shows a large gallstone within the lumen of the gallbladder. The gallstone reflects virtually all of the sound waves. Therefore, the edge of the stone is very bright on the screen and the tissues behind the stone are obscured by shadows because no sound waves make it past the stone. Video clip 13: Multiple gallstones: Multiple echogenic foci within the gallbladder lumen with shadowing behind. Video clip 14: Multiple gallstones: Three or more gallstones lie within the gallbladder with shadowing.
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Video clip 15 |
Video clip 16 |
Video clip 15: Full of stones: This gallbladder is full of stones. Many echogenic foci with shadowing are seen within the lumen of the gallbladder. Video clip 16: Layer of stones: Notice the very bright line of stones at the lower left aspect of the gallbladder with shadowing behind.
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Video clip 17 |
Video clip 18 |
Video clip 17: Very small stone: This video shows a very small stone that we missed in our department on first pass. Can you find it? Video clip 18: SIN sign: This gallstone lies in the neck of the gallbladder. The so-called SIN (Stone In the Neck) sign may be more indicative of cholecystitis in the correct clinical scenario.
Gallbladder wall polyps may be confused with gallstones. They are soft tissue masses attached to the wall of the gallbladder and differentiated from gallstones by their lack of mobility and shadowing (Video 19).
Video clip 19: Polyp: This patient has multiple
gallbladder polyps adhering to the wall.
The position of polyps in the gallbladder is important as they may
cause acute cholecystitis if they lodge in the neck of the gallbladder.
Gallbladder sludge is likely made up of very small stones making the bile
viscous and giving the bile echogenicity. Sludge is identified on
ultrasound as slightly hyperechoic material forming a meniscus within the
gallbladder lumen. Sludge may be a precursor to gallstones and has
been related to pathology such as acute cholecystitis and acute pancreatitis
(Video 20).
Video clip 20: Sludge: This gallbladder
is full of sludge. Several small gallstones are also found toward
the neck of the organ.
2. Sonographic Murphy’s Sign: The sonographic Murphy’s sign differs from Murphy’s sign identified on physical exam (arrest of inspiration on deep palpation of the right upper quadrant). Sonographic Murphy’s sign is positive when the point of maximal tenderness is identified in the right upper quadrant while the gallbladder is identified on the ultrasound monitor. Multiple points in the epigastrium and right upper quadrant must be tested with the ultrasound probe when the gallbladder is not demonstrated in order to properly evaluate this sign. The sensitivity of the sonographic Murphy’s sign is reported from 75-86 % with a positive predictive value of 92 % when combined with the finding of gallstones.(15,17)
3. Gallbladder Wall Thickness: The
normal gallbladder wall measures less than 4 mm. As detailed above,
the gallbladder wall is measured at the most narrow point of the anterior
wall in the short-axis. Care
must be taken to not measure the wall at an oblique angle (Video 21).
The gallbladder wall may be thickened in many disease states. Acute
cholecystis is the most common of these. Ascites and congestive heart failure
are the second and third most common cause of gallbladder wall thickening. Hepatitis
may also cause gallbladder wall edema. Gallbladder wall cancers may show
a thickened and/or calcified gallbladder wall.
Video clip 21: Thick
wall: This patient’s gallbladder wall is thickened to
7.1 mm. Note the difference between the gallbladder wall
edema andthe contracted wall we looked at earlier. There is also a small wedge
of pericholecystic fluid on the left.
4. Pericholecystic Fluid: Pericholecystic fluid (PCCF) is generally found in wedges around the acutely inflamed gallbladder wall. It is most often seen posterior to the gallbladder at the around the neck, but may also be seen layering on the anterior wall. Ascites makes evaluation of pericholecystic fluid due to gallbladder inflammation impossible, as the patient will have free fluid throughout their abdomen, including around their gallbladder (Video 22).
Video clip 22: Pericholecystic Fluid (PCCF): This
patient has a thick gallbladder wall and a small
wedge of free fluid
to the left of that thickened wall. It is subtle, but note the
dark area next to the gallbladder.
5. Dilated Common Bile Duct: The CBD may dilate when obstructed by a stone, a mass, or a stricture. The normal width of the CBD is 4 mm. Older patients may have a normally dilated duct up to 1mm for every decade past the age of 40. The CBD may be dilated up to 1cm normally after cholecystectomy (Video 23 & 24).
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Video clip 23 |
Video clip 24 |
Video clip 23: Dilated
CBD: This patient’s
CBD is enlarged to over 1 cm. The IVC demonstrates flow
near the
bottom of the screen. Above that is the portal vein. The
enlarged CBD is next. Video clip 24: Large CBD: A massively dilated
CBD may be very disorienting. Watch how these sonographers use power Doppler
ultrasound to differentiate the biliary tract from the vasculature in the
liver.
In the setting of acute cholecystitis, the common hepatic duct may be
dilated due to inflammation of the gallbladder wall neck and cystic duct
causing external pressure. This is a rare complication termed Mirizzi syndrome
and may lead to hyperbilirubinemia.
Gangrenous and emphysematous cholecystitis are serious complications of
acute cholecystitis that may be identified with ultrasound by the presence
of air within the gallbladder wall or lumen (Video 25). Air on ultrasound
is represented by “comet-tail” artifacts. Gallbladder perforation
may also be diagnosed by ultrasound. Findings of perforation include
significant amounts of pericholecystic fluid that may contain echogenic
material which may be walled off from the rest of the abdomen.
Video clip 25: Air
in the GB wall: There
are comet-tail artifacts extending down
from this gallbladder wall indicating
air due to emphysematous cholecystitis.
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Video clip 26: Duodenum mimicking
gallbladder filled with stones: The
duodenum adjoins the posterior aspect of the liver. At times, it
may appear as the gallbladder filled with stones. The air in the
duodenum appears as “dirty shadowing” .
The shadows are very indistinct,
rather than the clean shadows behind stones.
Video clip 27: Gallstone vs. Duodenum: The
duodenum sits very close to the gallbladder. So close
that the thickness
of the ultrasound beam may pick up parts of both, superimposing the duodenum
onto the gallbladder in the image. This can cause problems because
the duodenum may shadow due to air
leading the sonographer to believe there
is a gallstone within the gallbladder.
Video clip 28: WES sign: The Wall-Echo-Shadow
sign can make it very difficult to identify and evaluate the gallbladder. There
is a very strong echo at the rim of the stone and wall of the gallbladder. The
shadow is very thick and clean and extends through the liver.
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