Ultrasonography of the gallbladder
In this video, we'll show you when and how to perform an ultrasound scan of the gallbladder.
The gallbladder is a pear-shaped, hollow, fluid-filled organ that lies against the visceral
surface of the liver. The rounded lower end of the gallbladder,
the fundus, projects just below the right costal margin, a little medial to the midclavicular
line.
If you suspect gallstones, inflammatory changes, or masses of the gallbladder, an ultrasound
scan can help you narrow the differential diagnosis.
Ideally, the patient should have fasted before the scan. This is because in the fasting state,
the gallbladder is distended with unreleased bile, which allows for a better assessment.
The patient should be instructed to inhale deeply. Doing this shifts the liver -- and
with it the gallbladder -- in a caudal direction. This allows us to use the liver as an “acoustic
window.” Compared to air-filled bowel loops, liver parenchyma has a lower acoustic impedance,
enabling a much better assessment of the underlying gallbladder.
We'll now demonstrate how to scan the gallbladder, first in the long axis, then in the short
axis. Afterwards, we'll show you the normal findings and abnormal findings of a gallbladder scan.
We can use a curvilinear or phased array probe for these scans.
Long-axis view
Begin with your probe placed below the costal margin, just to the right of the midline.
Tilt the probe to "fan" through this region and locate the gallbladder.
It may be necessary to adjust the depth at this point. Once you've identified the gallbladder, rotate
or slide the probe as needed to obtain a full long-axis view.
In this view, the gallbladder fundus, body, and neck are visible.
Now, fan through the long-axis view by slowly tilting the probe, first caudally, then cranially.
As you can see, tilting in one direction fans through in the opposite direction.
So, with the probe oriented as shown here, tilting the probe caudally fans through the
lateral parts of the gallbladder, and tilting the probe cranially fans through the medial
parts. To be able to confidently rule out wall abnormalities,
for example, you need to fan all the way through the gallbladder, until the anechoic lumen
disappears completely.
Short-axis view
To obtain a short-axis view, rotate the probe 90°. The probe marker then faces toward the
patient's right side. In this view, the gallbladder has a rounded appearance.
Keeping the probe orientation the same, slide the probe along the gallbladder to scan through
it in short-axis view. First slide toward the fundus until the gallbladder disappears
completely. Then slide in the opposite direction until
the gallbladder neck and cystic duct are visible.
Normal findings
A normal gallbladder wall should appear as a narrow, sharply demarcated, hyperechoic
line. In a fasted patient with a full gallbladder,
the wall should be at most 3 mm thick. In a postprandial patient, the wall often appears
thicker; don't mistake this for a pathological finding.
Abnormal findings
An abnormally thickened gallbladder wall may suggest acute cholecystitis. As you can see
here, this may also result in a layered appearance, with a hypoechoic layer of edema between two
hyperechoic wall layers. This is called the double-wall sign.
Because the gallbladder is filled with fluid, the lumen is normally anechoic.
Hyperechoic structures within the lumen may represent gallstones or pathologies of the
gallbladder wall, such as polyps. Gallstones typically result in acoustic shadowing
and may move around within the gallbladder if the patient changes position.
Polyps are outgrowths of the wall and therefore not mobile. They also do not usually have an acoustic
shadow.
Okay, now that you have an overview of gallbladder ultrasound skills, check out the POCUS article
on AMBOSS.