Gallbladder

The gallbladder is a pear-shaped sac lying on the visceral surface of the right lobe of the liver in a fossa between the right and caudate lobes. It is composed of a fundus, body, and neck. It serves as a storage vessel for the bile, synthesized by the liver. The neck contains a mucosal fold, known as Hartmann’s pouch. This pouch represents a common location for gallstones to lodge and cause cholestasis.

Ultrasound examination

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The gallbladder is surrounded by peritoneum and is in direct relation to the visceral surface of the liver. There is the inferior border of the liver and the anterior abdominal wall anteriorly and superiorly to the gallbladder. The transverse colon and proximal duodenum lie posteriorly. Inferiorly, the biliary tree and remaining parts of the duodenum are located.

A normal gallbladder should look like a pear-shaped uniformly anechogenic sac. Sometimes we can also find gallbladder folds, which are seen quite commonly and are normal (pay attention if you see a pathology such as calliculi within a compartment created by a fold) with an iso- or hyperechoic wall thinner than 3 mm and anechogenic content. Its size varies depending on the amount of bile. It is approximately 10 cm long during fasting. The normal gallbladder wall appears as a pencil-thin echogenic line. The thickness of the gallbladder wall depends on the degree of gallbladder distention, and pseudo thickening can occur in the postprandial state. It is always measured through the acoustic window of the liver, meaning the wall of the gallbladder should be touching the liver parenchyma. The gallbladder empties after a meal, so the patient needs to fast for 6 hours beforehand. If the patient has not fasted, the gallbladder may not be seen or may appear collapsed and incompletely visualised.

Gallblader folds

Available at: https://www.ultrasoundpaedia.com/normal-gallbladder/ (Accessed: 19 November 2019).

Anatomy of billiary system

Available at: https://www.ncbi.nlm.nih.gov/books/NBK65963/bin/CDR0000658899.jpg (Accessed: 7 March 2020).

Gallbladder, cystic duct, common hepatic duct and common bile duct

Available at: https://media.springernature.com/original/springer-static/image/art%3A10.1007%2Fs40477-019-00362-9/MediaObjects/40477_2019_362_Fig2_HTML.jpg (Accessed: 7 March 2020).

Gallbladder, cystic duct, common hepatic duct and common bile duct.

Available at: https://media.springernature.com/original/springer-static/image/art%3A10.1007%2Fs40477-019-00362-9/MediaObjects/40477_2019_362_Fig2_HTML.jpg (Accessed: #March 2020)

The emptying of the gallbladder

Bile is secreted from the gallbladder in response to an enzymatic stimulus. The stimulus causes the contraction of the smooth muscle in the gallbladder. This is the reason why the gallbladder is easier to find on an empty stomach. The gallbladder begins to empty when the food enters the duodenum and begins to be digested, especially if it contains fat. The most potent stimulus for the gallbladder contractions is the hormone cholecystokinin. The stimulus for its release into the blood from the duodenal mucosa is mainly the fatty food itself entering the duodenum. For emptying, the sphincter of Oddi needs to relax.

There are at least three different factors that facilitate this process. Firstly, cholecystokinin itself has a relaxing effect. Secondly, rhythmic contractions of the gallbladder transmit peristaltic waves down the common bile duct to the sphincter of Oddi, causing a leading wave of relaxation that partially inhibits the sphincter in advance of the peristaltic wave. Thirdly, the intestinal peristaltic waves travel over the wall of the duodenum. The relaxation phase of each of these waves strongly relaxes the sphincter of Oddi along with the relaxation of the muscles of the gut wall.

Common bile duct (ductus choledocus)

The duct system for the passage of bile extends from the liver, connects with the gallbladder, and empties into the descending part of the duodenum. Bile is initially secreted from hepatocytes and drained from both lobes of the liver via canaliculi, intralobular ducts, and collecting ducts into the left and right hepatic duct. These ducts combine to form the common hepatic duct, which runs near the liver, with the hepatic artery proper and portal vein in the free margin of the lesser omentum. As the common hepatic duct continues to descend, it is joined by the cystic duct. The cystic duct comes from the gallbladder and allows bile to flow in and out of the gallbladder for storage and release. The common hepatic duct and cystic duct combine to form the common bile duct.  At the merging point, the bile duct lies to the right of the hepatic artery proper and usually to the right of and anterior to the portal vein. The bile duct descends and passes posteriorly to the first part of the duodenum and head of the pancreas. Here, it is joined by the main pancreatic duct, forming the hepatopancreatic ampulla, which then empties into the duodenum via the major duodenal papilla, regulated by a muscular valve, the sphincter of Oddi.

 

The normal internal diameter of the common bile duct on the ultrasound is 6 mm. The size of the common bile duct is a predictor of biliary obstruction. Therefore, its measurement is an important component in evaluating the biliary system.

Billiary system

Available at: http://www.liberaldictionary.com/wp-content/uploads/2018/11/right-hepatic-duct.jpg (Accessed: 19 November 2019).

Ductus choledocus and portal vein, PAME Maribor
Gallbladder, cystic duct, common hepatic duct and common bile duct.

Available at: https://media.springernature.com/original/springer-static/image/art%3A10.1007%2Fs40477-019-00362-9/MediaObjects/40477_2019_362_Fig2_HTML.jpg (Accessed: #March 2020)

Ultrasound examination

When there is a clinical indication, ultrasound can always be used to confirm or exclude our clinical diagnosis. The patient stays in the same supine position as in the clinical examination. The probe is placed on the patient in the transversal or coronal plane with the marker pointing to either the patient’s right side or his head. The examination can begin in epigastrium, just inferior to the xiphoid process, where the liver is located. The probe is slowly slid towards the patient’s right side while maintaining the subcostal position of the probe. The gallbladder should be located at around 7 cm laterally to the xiphoid process below the ribs. We can ask the patient to inhale, which allows the gallbladder to come closer to the probe. If the gallbladder is still not found, we can look for it in between the ribs. Examining the liver, we can see:

  • hepatic veins,
  • portal veins with the echogenic wall,
  • bile ducts and gallbladder (it can be distinguished from blood vessels with color Doppler),
  • arterial vessels.

Once the gallbladder is located, we can look for different pathologies, such as gallbladder sludge, gallstones, wall thickening, and positive sonographic Murphy sign.

https://youtu.be/Xsj5j2hzjtA

Wall thickening

Wall thickening of the gallbladder is defined as the wall measuring more than 3 mm in diameter. It can appear physiologically after meals due to contractions of the wall. It is crucial to ask the patient when he/she had the last meal. He/she should be fasting for at least 6 hours before the examination. If the wall is still thickened after 6 hours of fasting, the gallbladder is usually inflamed. Wall thickness is measured on the anterior wall (facing the liver) at the thinnest part.

Wall thickening

Available at: https://radiologyassistant.nl/img/containers/main/gallbladder-wall-thickening/a509797711a4d1_Fig-1A.jpg/4b4e4335a7223a777673558afc21e0b3.jpg (Accessed: 19 November 2019).

Sonographic Murphy sign (SonoMurphy)

A sonographic Murphy sign is caused by exerting pressure over the gallbladder with the ultrasound probe. If discomfort and tenderness are present during the pressure is applied, the sign is positive, and cholecystitis is likely present.

Gallstones

Gallstones are concretions that occur anywhere within the biliary system, most commonly within the gallbladder. They occur because certain substances in bile are present in concentrations that approach the limits of their solubility. When bile is concentrated in the gallbladder, it can become supersaturated with these substances. They can precipitate from the solution as microscopic crystals. The crystals are trapped in the gallbladder mucus, producing gallbladder sludge. Over time, the crystals grow, aggregate, and fuse to form macroscopic stones. When stones are formed within the gallbladder, the pathology is called cholecystolithiasis in contrast to choledocholithiasis, where stones are located within the bile ducts. Biliary microlithiasis refers to gallstones, which are less than 3 mm in diameter.

There are several types of gallstones:

  • cholesterol gallstones (80%),
  • calcium, bilirubin and pigment gallstones,
  • mixed gallstones (When cholesterol stones become colonized with bacteria, lytic enzymes from bacteria and leukocytes hydrolyze bilirubin conjugates and fatty acids. As a result, cholesterol stones may accumulate a substantial proportion of calcium bilirubinate and other calcium salts).

Approximately 10% of the world population has had gallstones at least once in their life. Women are two times more likely to have them as men. The prevalence also rises with age in both sexes. Genetics may as well play a role in the formation of the stones. When it comes to risk factors, there is a mnemonic we can use to remember them more easily, called the »5F rule«. It refers to:

  1. Fair – more prevalent in the caucasian population;
  2. Fat – BMI over 30;
  3. Female;
  4. Fertile – one or more children;
  5. Forty – age over 40;

Stones can occur in young patients with a positive family history. Therefore, many authors refer to the rule as the »5F rule, « or they substitute the »forty factor« for »family factor«.

Gallstones may be symptomatic in only 25% of cases. Symptoms and complications result from effects occurring within the gallbladder or from stones that escape the gallbladder to lodge in the common bile duct. The most common presentation is biliary colic. Because the stone obstructs the outflow of bile, intraductal pressure rises, and peristaltic contraction leads to severe visceral pain in the epigastric area. The pain may radiate to the right scapular tip. Episodes of pain are sporadic and unpredictable. However, they usually begin postprandially and last 1-5 hours. Pain cannot be relieved by emesis, antacids, defecation, flatus, or positional changes. It is sometimes accompanied by diaphoresis, nausea, and vomiting. Nonspecific symptoms may be present as well, such as indigestion, dyspepsia, belching, or bloating.

Ultrasound examination

The sensitivity for cholelithiasis is 89.8% and specificity 88%.

In ultrasound examination we firstly locate the gallbladder. Gallstones appear as a hyperechoic, well-defined focal lesions inside an anechogenic sac (gallbladder) and are throwing an acoustic shadow behind (if bigger than 1 mm). If the patient is symptomatic, we pay special attention to the gallstones located in the fundus of the gallbladder. Most gallstones exhibit gravitational dependence and will move with patient repositioning.

Cholelitiasis

Available at: https://www.thepocusatlas.com/hepatobiliary/ (Accessed: 19 November 2019).

Liver, gallbladder wall and gallstone with posterior shadowing

Available at: https://www.quora.com/What-do-gallstones-look-like-on-an-ultrasound (Accessed: 19 November 2019).

Gallbladder polyps

Lesions that project interiorly from the gallbladder wall into the gallbladder are called gallbladder polyps. In the majority of cases, polyps are found incidentally during a routine abdominal ultrasound. Even though most of the gallbladder polyps are benign, malignant polyps are present in some cases. The early detection and appropriate early measures are essential for curative treatment and long-term survival. The primary goal in the management of gallbladder polyps is to prevent the development of gallbladder carcinoma.

 

Polypoid lesions of the gallbladder represent a wide spectrum of findings. Gallbladder polyps are classified as benign or malignant. Benign gallbladder polyps are subdivided into pseudotumors (cholesterol and inflammatory polyps, cholesterolosis and hyperplasia), epithelial tumors (adenomas), and mesenchymal tumors (fibroma, lipoma, and hemangioma). Malignant gallbladder polyps are gallbladder carcinomas.

Ultrasound examination

The polyps can be located, counted, and measured with ultrasound. We can view the three layers of the gallbladder wall and any possible abnormalities. The polyps appear as fixed, hyperechogenic material protruding into the lumen of the gallbladder, with or without an acoustic shadow. The sensitivity of abdominal ultrasound for the diagnosis of gallbladder polyps is superior to both oral cholecystography and CT. The cholesterol polyp is shown as a mass with similar echogenicity to the gallbladder wall and will have no shadow cone. However, the distinction is difficult to make, and the status of polyps as benign or malignant cannot be determined with the abdominal ultrasound alone. The differential diagnosis of polyps less than 20 mm with transabdominal ultrasound remains difficult. Sonographic differentiation between benign and malignant polyps (and calculus disease) relies greatly on the size of a single nonmobile lesion within the gallbladder. A gallstone impacted within the gallbladder wall may be easily mistaken for a polyp on ultrasound scanning.

 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3359430/

Gallbladder polyp

Andrén-Sandberg, Å. (2012) ‘Diagnosis and management of gallbladder polyps’, North American Journal of Medical Sciences. Wolters Kluwer -- Medknow Publications, pp. 203–211. doi: 10.4103/1947-2714.95897

Acute cholecystitis

Cholecystitis is an inflammation of the gallbladder that occurs most commonly because of an obstruction of the cystic duct by gallstones arising from the gallbladder.

The most common presenting symptom of acute cholecystitis is upper abdominal pain. Signs of peritoneal irritation may be present, and the pain may radiate to the right shoulder or scapula. Pain frequently begins in the epigastric region and then localizes to the right upper quadrant. Pain may initially be colicky but almost always becomes constant. Nausea and vomiting are generally present, and fever may be noted.

Gallstones are not always the reason for inflammation. In less than 10% of the cases, acute cholecystitis is caused by vasculitis, polytrauma, severe burns, or chemotherapy. In cases like this, we refer to the condition as acute acalculous cholecystitis. Patients with acalculous cholecystitis may present with fever and sepsis alone, without the history or physical examination findings consistent with acute cholecystitis. The sensitivity for cholecystitis is 82-91% and specificity 66-95%.

Differential diagnosis includes:

  • choledocholithiasis,
  • pancreatitis,
  • peptic ulcer disease,
  • acute hepatitis,
  • liver abscess.

In acute cholecystitis ultrasound examination we firstly locate the gallbladder. The findings that increase the possibility of acute cholecystitis diagnosis include gallstones, dilation of the gallbladder, wall thickening (> 3mm), wall edema and pericholecystic fluid. However we shall take into consideration that many cholecystitis findings are nonspecific.

Acute cholecystitis

Available at: https://jetem.org/wp-content/uploads/2018/01/Acute-Cholecystitis-Ultrasound-Annotated.-JETem-2018.jpg (Accessed: 19 November 2019).

Thickened gallbladder wall

Dilated ductus choledochus

Resources

Gray, H., Carter, H. V. (Henry V. and Davidson, G. (2013) Gray’s Anatomy. Arcturus Publishing Ltd.

The Gallbladder - TeachMeAnatomy. Available at: https://teachmeanatomy.info/abdomen/viscera/gallbladder/ (Accessed: 9 March 2020).

Hall, J. and Guyton, A. (2016). Guyton and Hall textbook of medical physiology. Philadelphia: Elsevier.

Hansel, J. (2016). PACE - POCUS Assisted Clinical Exam A Modular Curriculum for Teaching Point-of-Care Ultrasound to Undergraduate Med Students.

TeachMeAnatomy | The Gallbladder - Biliary Tree - Gallstones | Teachmeanatomy.info. Available at: https://teachmeanatomy.info/abdomen/viscera/gallbladder (Accessed: 7 March 2020).

The Radiology Assistant : Gallbladder - Wall Thickening. Available at: https://radiologyassistant.nl/abdomen/gallbladder-wall-thickening (Accessed: 7 March 2020).

Gallstones | Radiology Reference Article | Radiopaedia.org. Available at: https://radiopaedia.org/articles/gallstones-1?lang=gb (Accessed: 7 March 2020).

Imaging in Gallstones (Cholelithiasis): Practice Essentials, Radiography, Computed Tomography (2018). Available at: https://emedicine.medscape.com/article/366246-overview#a5 (Accessed: 9 March 2020).

Gallstones (Cholelithiasis): Practice Essentials, Background, Pathophysiology (2019). Available at: https://emedicine.medscape.com/article/175667-overview#a3 (Accessed: 9 March 2020).

Andrén-Sandberg, Å. (2012) ‘Diagnosis and management of gallbladder polyps’, North American Journal of Medical Sciences. Wolters Kluwer -- Medknow Publications, pp. 203–211. doi: 10.4103/1947-2714.95897.

Cholecystitis: Practice Essentials, Background, Pathophysiology (2019). Available at: https://emedicine.medscape.com/article/171886-overview (Accessed: 9 March 2020).

What are the different types of gallstones?. Available at: https://www.webmd.com/digestive-disorders/qa/what-are-the-different-types-of-gallstones (Accessed: 9 March 2020).