Ultrasound Of The Gallbladder

ULTRASOUND OF THE GALLBLADDER

SONOGRAPHY OF THE GALLBLADDER

Since ultrasound is the primary imaging modality in the evaluation of the gallbladder, it is a “bread and butter” type of study.

In patients with right upper quadrant symptoms, ultrasound not only evaluates the gallbladder, but adjacent structures such as liver, bile ducts, pancreas, right kidney and great vessels.

SONOGRAPHY OF THE GALLBLADDER

The gallbladder is an excellent organ to image by sonography, because it is a fluid-filled structure with no internal echoes. It is visualized as an anechoic pear-shaped structure outlined by a smooth thin wall. Any abnormality within the gallbladder becomes outlined by the bile and is easily seen.

SONOGRAPHY OF THE GALLBLADDER

As with any structure imaged by ultrasound, it must be examined in two perpendicular (orthogonal) planes in order to be able to reconstruct a proper 3-dimensional mental picture of the object and to avoid artifacts

SONOGRAPHY OF THE GALLBLADDER

This is a transverse section of the gallbladder. Based on its purely fluid content, the gallbladder is used as a standard of reference for fluid-containing structures in the right upper quadrant. Cysts in the liver and right kidney can be compared to the gallbladder, as long as they are at similar depths.

SONOGRAPHY OF THE GALLBLADDER

If the echogenicity of their contents is the same as that of the gallbladder, then they are simple cysts. If their contents is more echogenic, then the cysts contain true echoes and are not simple cysts.

One should be mindful of the fact that it is possible to have a congenital duplication of the gallbladder, which is rare. Also there are structures that can mimic the gallbladder. These include omental cysts, enteric duplication cysts, choledochal cysts, aneurysms, abscesses.

GALLBLADDER MEASUREMENTS

The size of the gallbladder is quite variable, so that it is not a very useful indicator of disease.

In general the normal gallbladder is < 5cm transversely, and < 10cm longitudinally.

A gallbladder larger than this is usually abnormally enlarged, such as a Courvoisier gallbladder, which enlarges on the basis of distal extrahepatic biliary duct obstruction.

NON-DISTENDED GALLBLADDER

A post-prandial gallbladder cannot be differentiated from an abnormal diseased, contracted gallbladder.

An empty gallbladder is difficult to scan and results are unreliable. The gallbladder should always be examined in the fasting state, when it is maximally distended.

NON-DISTENDED GALLBLADDER

This is accomplished by an overnight fast, usually starting by midnight before the scan. The ultrasound is usually performed in the morning, when the bowel is quiet and abdominal gas is at a minimum. If the patient has not had a proper overnight fast, fasting for approximately 8 hours is considered adequate.

INADEQUATE FAST

An inadequate fast may result in slight gallbladder wall contraction and mild wall thickening, which in turn may lead to incorrect diagnosis.

NON-FASTING GALLBLADDER

One should avoid the temptation of scanning the gallbladder without a proper fast. Even if gallstones are visualized, the complete diagnosis may be compromised because of suboptimal visualization, as in this case of a non-fasting patient with right upper quadrant pain.

NON-FASTING GALLBLADDER

Two gallstones are seen in the fundus (short arrows), but the potentially obstructing stone (long arrow) in the gallbladder neck was not seen until the patient underwent a proper fast. In retrospect the stone was present on the original image shown here (long arrow).

ANATOMY OF THE GALLBLADDER

The fundus is the rounded curved end of the gallbladder. The body is the central portion, while the neck is the tapered part.

The gallbladder is connected to the biliary system by the cystic duct, which contains numerous folds called valves of Heister. Stones are easily trapped within these folds.

ANATOMY OF THE GALLBLADDER

After the cystic duct joins the common hepatic duct, the extrahepatic bile duct is called the common bile duct.

GALLBLADDER FOLDS

Folds within the gallbladders are non-pathologic. A particular fold, called the junctional fold, normally occurs in the mid to proximal end of the gallbladder, closer to the gallbladder neck (arrow). This fold may cause an acoustical shadow due to an artifact and should not be mistaken for a stone or calcification.

GALLBLADDER SEPTATIONS

Rarely gallbladders contain true septations. These are congenital in origin and are of no clinical significance. A gallbladder folded back upon itself may simulate septations. In fact, sometimes during different degrees of inspiration and expiration, one can observe the gallbladder folding and unfolding. This is of no known clinical consequence.

ANATOMIC VARIANT: THE PHRYGIAN CAP

When the fundus of the gallbladder folds over on itself, it creates the appearance of a cap, called the “phrygian cap” (arrow). Occurring in 4% of the population, this is one of the better known anatomic variants of the gallbladder. It is asymptomatic and unrelated to disease.

THE GALLBLADDER NECK

The gallbladder neck often has a convoluted tortuous course, which becomes a trap for calculi. The neck usually does not contain enough bile to allow for its recognition. Calculi within the neck of the gallbladder are often not imaged for this reason and this is one cause of false negative sonograms for cholelithiasis.

CYSTIC DUCT

The convoluted appearance of the cystic duct (large arrow) is well demonstrated in this split-screen sonogram. Usually the cystic duct is not this well-filled with bile, therefore small stones within the cystic duct are not readily apparent and contribute to false negative diagnoses.

CYSTIC DUCT AND BILE DUCT

In this post-operative case, the cystic duct remnant (arrows) is unusually well seen because there was distal ductal biliary obstruction. The cystic duct is rarely identified due to lack of distention with bile.

GALLSTONES

The incidence of gallstones is 10-20% of the population in the USA.

Cholecystectomy is the second most common abdominal surgery in the USA with well over half a million cholecystectomies performed annually.

There is a variety of symptomatology associated with gallstones.

Gallstones occur with higher frequency in females than in males, more so in obese patients and during pregnancy.

GALLSTONES

• There are strict sonographic criteria for gallstones. They include:
• an echogenic focus, which casts an

acoustical shadow, and is

All three criteria must be met, before a gallstone is diagnosed. This ensures the high accuracy of ultrasound in the diagnosis by decreasing the number of false positives.

GALLSTONES

Demonstration of mobility of echogenic foci in the gallbladder is essential to the diagnosis of cholelithiasis. A significant change in patient position is required to demonstrate mobility, for example, a change from supine to a steep decubitus or erect position.

GALLSTONES

Even though these calculi are small, they manifest as echogenic foci that demonstrate acoustical shadowing. Mobility of the stones must be demonstrated for definitive diagnosis.

GALLSTONES

Demonstration of mobility of echogenic foci in the gallbladder is essential to the diagnosis of cholelithiasis. In this case it also helps to demonstrate another essential criterion for gallstone diagnosis, i.e. shadowing. Individually the stones do not shadow, but when they pile up on top of each other, they cause collective shadowing.

SMALL CALCULI

Another example of mobility and collective shadowing. In this case, when the patient is supine, there are multiple tiny calculi (arrows) that layer along the back wall of the gallbladder, but individually they do not shadow. After placing the patient in the erect position, the calculi (arrow) move into the fundus of the gallbladder and collectively create acoustical shadowing, thus acting like a single large stone. Now all three criteria have been satisfied.

GALLSTONES

As gallstones rub against each other, over time they may acquire flat surfaces. These are called faceted stones, because they are like the cut surfaces on gemstones.

Ultrasound Of The Gallbladder

Occasionally unusual presentations of gallstones are encountered, as in this case of calculi with hypoechoic centers and hyperechoic rims. These calculi do not have obvious shadows, possibly because at this stage they are “soft stones”. With time, as they solidify, they acquire shadows.

FALSE GALLSTONES

Adherence to the strict criteria for gallstones will help to decrease false positive ultrasound studies, which lead to unnecessary surgery.

A pocket of gas (arrow) in a loop of bowel immediately adjacent to the gallbladder may create the false appearance of a gallstone, as in this case (A), because it has the appearance of an echogenic focus, which creates an acoustical shadow and appears to be inside the gallbladder.

FALSE GALLSTONES

Due to complex physical factors particularly beam width, the bright echoes from the gas are written into the lumen of the gallbladder on the longitudinal scan. However, when the transducer is turned 90 degrees (B), the gas echoes (arrow) are written correctly, outside of the gallbladder (open arrow), immediately beneath it.

FALSE GALLSTONES

Such false calculi can be avoided by always imaging calculi in two perpendicular projections or by changing position of the patient and causing the gas to shift.

FALSE GALLSTONES

This is another example of false gallstones. On the longitudinal image (A) rounded hyperechoic structures that cause some shadowing (false gallstones) appear to be within the gallbladder lumen. However, when a 90 degree transverse scan is taken (B), we can see that the hyperechoic shadowing areas actually extend beyond the gallbladder.

FALSE GALLSTONES

They are situated very close to the gallbladder, but they are outside the lumen of the gallbladder. They represent air or gas within bowel adjacent to the gallbladder.

FALSE GALLSTONES

The shadowing from air or gas is described as “dirty”, because it contains reverberation artifacts and scattered echoes. In contradistinction, shadows from stones are “clean and sharp”, lacking such extra echoes.

FALSE GALLSTONES

Here is a case of false gallstones created by small bubbles of gas within the duoenum located immediately under the gallbladder. Based on their size, appearance and shadow production, the echogenic foci (arrow) simulate calculi within a small amount of sludge. These were proven not to be calculi within the lumen of the gallbladder, when they disappeared after position change.

CALCULI OR GAS?

In this case there is a bright linear band along the back wall of the gallbladder (A). Such an appearance may be due to multiple tiny calculi layering along the dependent wall of the gallbladder or gas in a long segment of bowel immediately adjacent to the gallbladder.

CALCULI OR GAS?

Changing position of the patient shifts the echoes in the lumen of the gallbladder (B). Numerous tiny stones clump together and fill approximately half of the lumen of the gallbladder.

CHECK THE CYSTIC DUCT

Whether gallstones are present or not, special effort should be devoted during the scan to examine the area of the cystic duct. There is usually not enough bile to outline a calculus (arrow), which may be causing obstruction.

Transverse views help to demonstrate the calculus.

Summary word slide

Technically all calculi shadow, but it is not always possible to have optimal technique in every patient in order to demonstrate the shadowing.

SHADOW PRODUCTION

Investigators have shown that all stones shadow regardless of their chemical composition or shape. Optimal sonographic technique is important for the production of shadowing from gallstones.

If a shadow is not produced by the standard 3.5 MHz transducer, a higher frequency probe should be used, usually a 5.0 MHz.

SHADOW PRODUCTION

Gain and power settings should be as low as possible in order to visualize thin shadows, which may be overwritten by noise and scattered echoes.

SHADOW PRODUCTION

A stone should be positioned within the focal zone and within the center of the ultrasound beam. The patient’s position may need to be changed in order to optimize the position of the stone in relation to the transducer. For example, the patient may need to be rolled toward the left so that the gallbladder falls closer to the abdominal wall and into the focal zone

EXPERIMENT WITH GALLSTONE AND FOCAL ZONE

This in vitro experiment shows that an acoustical shadow is best produced when an object, in this case a gallstone, is in the focal zone. A shadow is not produced when the object is in the near zone or far zone of the transducer.

EXPERIMENT WITH GALLSTONE AND FOCAL ZONE

In this experiment an actual gallstone was scanned in a water bath with the same transducer, which has a fixed focal zone of 6 centimeters. In the first picture the gallstone is seen on top of the tissue equivalent medium at a depth of 3 cm (in the near field). There is no shadow produced.

Not all shadows in the vicinity of the gallbladder are caused by stones

Ultrasound Of The Gallbladder

Shadows from sources other than gallstones and bowel gas occur related to the gallbladder and they may cause false positives for the diagnosis of cholelithiasis. Calculi must not be diagnosed by means of visualizing an acoustic shadow alone.

Ultrasound Of The Gallbladder

Shadows may be seen from the edges of the gallbladder (arrows). They are due to reflection or refraction artifacts, which occur at a specific angle from the curved edges of structures, therefore they are also called critical angle shadows. These shadows come from the curvature of the normal gallbladder wall, not from pathologic changes, such as calcification.

CRITICAL ANGLE SHADOWS FROM THE GALLBLADDER

Critical angle shadows can also come from a junctional fold in the gallbladder, when the beam strikes the fold at a specific angle, causing shadowing. Such a shadow should not be mistaken as coming from a calculus.

SHADOWS NEAR THE GALLBLADDER

Reflection and refraction artifacts (critical angle shadows, arrows) from curved edges of structures may result from the tortuous neck of the gallbladder, as shown in the slide above. These shadows disappear when the angle of incidence is changed. A shadow coming from a true source would be reproducible from different angles.

As a result of its tortuous course the curved edges may cause shadows (small arrows), which should not be mistaken as coming from calculi (a false positive for cholelithiasis).

SHADOWS NEAR THE GALLBLADDER

Surgical clips (arrow), liver calcifications, and air within bile ducts cause bright reflectors and shadowing and may simulate cholelithiasis especially in the neck region or within bile ducts (choledocholithiasis).

When echogenic foci are in such close proximity, they may appear to be inside, rather than adjacent to, the gallbladder or bile ducts. In order to eliminate error in diagnosis, always scan the area in two perpendicular planes.

NON-VISUALIZATION OF THE GALLBLADDER

When the gallbladder is not visualized, possibilities include any of the above mentioned causes. Chronic cholecystitis may present with a collapsed, stone-filled gallbladder, which is difficult to recognize. Gallbladder carcinoma may obliterate the lumen of the gallbladder as it proliferates and grows around gallstones. Obstruction of the biliary tree proximal to the cystic duct does not allow bile to enter the gallbladder. Congenital absence of the gallbladder is rare.

NON-VISUALIZATION OF GB

WHAT TO DO

• Use main lobar fissure
• WES sign
• Double arc shadow sign
• Examine type of shadow: clean vs dirty
• Change patient position to shift gas

Administer water into duodenum to displace gas

FINDING THE NON-VIZ GALLBLADDER

In situations where the gallbladder is not visualized, it is helpful to find the main lobar fissure (also called the main or major interlobar fissure), which is seen as a white line extending from the porta hepatis toward the gallbladder. This line “points” to the gallbladder fossa.

DOUBLE ARC SHADOW SIGN

When the gallbladder is not immediately apparent, it may be filled with or collapsed around one large or multiple stones. In such a case it is useful to look for the “double arc shadow” or the WES sign (wall-echo-shadow). The wall (W) of the gallbladder is seen as a white line contrasted by a small amount of anechoic bile between it and the echogenic focus (E) of the stone, which causes a distal shadow (S). In situations where there is very little bile in the gallbladder, the two curved echogenic lines from the wall and the stone are barely separated by a thin stripe of fluid.

FINDING THE NON-VIZUALIZED GALLBLADDER

Even a small amount of bile is helpful to identify a gallbladder that is not so readily apparent.

FINDING THE NON-VIZ GALLBLADDER

When there is a shadow in the area of a non-visualized gallbladder, the appearance of the shadow should be analyzed. Calculi create a clean, sharp shadow with few internal reverberations, as in this case.

One should also try to delineate the overall shape of the shadowing structure. Transversely the shape of a stone-filled gallbladder is rounded, but when the transducer is turned 90 degrees, it should become elongated in its longitudinal diameter (see next slide).

BOWEL GAS NEAR THE GALLBLADDER

Bowel gas shadowing has a different appearance, in that it contains many reverberations, giving the shadow a “dirty” appearance. In this slide S1 is a clean, sharp shadow caused by a stone-filled gallbladder. S2 is a dirty shadow from adjacent bowel gas.

(S1 is along the longitudinal length of the stone-filled gallbladder.)

SHADOWS

Here is another example of a clean, sharp shadow (S1) from gallbladder calculi and a dirty shadow (S2) caused by reverberations from a pocket of bowel gas adjacent to the gallbladder.

NON-SHADOWING ECHOGENIC FOCI IN GB

When echogenic foci in the gallbladder do not shadow, their chance of being calculi decreases significantly (accuracy of diagnosis is 80%), because the differential diagnosis includes many possibilities:

GALLBLADDER POLYPS

Polyps are echogenic round masses attached to the gallbladder wall. They are distinguished from small calculi, because they do not move with position change and do not cast acoustical shadows.

(It should be noted that it is not possible to totally exclude calculi, because some calculi may be adherent to the gallbladder wall and may not shadow due to suboptimal technical factors.)

GALLBLADDER POLYPS

Polyps are often multiple, usually less than 8-10 mm in size. Most polyps are adenomatous polyps, some are cholesterol polyps. As long as the masses are small, smoothly marginated, less than 8-10 mm in diameter and connected to the wall by a narrow stalk, they are considered to be polyps and there is no clinical concern for another etiology.

Some of these polyps appear to be floating in the lumen, but they are actually attached to the wall by narrow stalks.

CHOLESTEROL POLYPS

Whether they are found in cholesterol polyps, stones or deposited in the sinuses created by adenomyomatosis, cholesterol crystals cause characteristic V-shaped reverberation artifacts, called comet-tail artifacts, as shown in this case of cholesterol polyps. The cholesterol crystals cause reverberation of the sound beam within or between the cholesterol crystals.

GALLBLADDER MASS

If a mass attached to the gallbladder wall does not meet the criteria for a polyp, then close clinical correlation and follow-up are warranted, because malignancy cannot be excluded. A carcinoma in an early stage becomes a possibility.

• There is concern for malignancy if a mass:
• has irregular borders,
• is larger than 8-10 mm,

has a broad-based connection to the wall.

The intraluminal mass in this slide is a suspicious mass. A malignant tumor, although rare, cannot be excluded. Fortunately, this was proven to be a polyp.