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Acute Cholecystitis

Emergency physcians and trainees who have been trained in bedside US for cholecystitis are as accurate as a formal scan performed by the radiology department (1). There are several features of acute cholecystitis which can be seen on bedside US. The positive predictive value for gallstones + thickened GB wall and sonographic Murphey's is >92% (2). 

FEATURES OF ACUTE CHOLECYSTITIS 

1. Gall stones 

2. Sonographic Murphey's

3. Thickened GB wall >3mm

4. Pericholecystic fluid

5. Increased vascularity to GB wall

In the septic or jaundiced patient, have a look at the CBD for ascending cholangitis or CBD obstruction. 

GALL STONES

Like all calcium containing structures, gall stones are hyperechoic (bright white) on US with a dense shadow posteriorly. This makes them easy to pick. Just beware that bowel gas can also cause shadowing so make sure to image the structure in two planes to make sure it's blind ending GB and not a loop of intestine.

GB in trans containing a large hyperechoic stone with a dense shadow

GB in long axis with multiple stones collecting at the GB neck

Smaller stones may not cause shadows. But usually there are several small stones which makes it easier. 

If you see stones, carefully evaluate the neck of the GB for impacted stones. If seen, ensure to change the patient position (eg to sitting/ lateral decubitus) and make sure the stones are mobile and settle in the fundus of the GB. 

Impacted stone in GB neck (note thickened GB wall and trace pericholecystic fluid)

patient supine: stone at the GB neck

patient sitting, stones have moved to the fundus of the GB

In my experience, stones stuck in the GB neck eventually lead to acute cholecystitis even if the patient has no other features of inflammation. So in patients with suspected biliary colic and resolved pain, always ensure the neck of the GB is free of stones. If there are stones stuck in the GB neck, ensure adequate FU and instructions to return or admit for observation. 

Polyps are common in the GB wall and may look like stones. However, they are not mobile and they do not cause shadowing. Polyps larger than 1cm should be referred for formal scanning and follow up to exclude malignancy.

SLUDGE

GB with sludge collecting at the neck. Note that there is nice posterior acoustic enhancement which you woukd expect from a fluid filled structure

Sometimes you may see sludge in the GB. This usually looks like hypoechoic fluid without shadowing (3). Small stones within the sludge could cause shadowing. 

THICKENED GB WALL

The normal GB wall is <3mm. In acute cholecsystitis the GB wall is usually 5mm or more. 

GB wall thickening has a wide differential. Most commonly, global wall thickening occurs without inflammation due to ascites from liver or right heart failure, hypoalbuminaemia etc. Malignancy is another cause of thickening (4). 

Localised (or diffuse) thickening may occur due to a condition called adenomyomatosis. This is a benign condition which has a characteristic appearence of commet tails descending into the GB lumen from the wall. 

GB trans: Adenomyomatosis at the fundus 

Hyperechoic locules within the GB wall with ring down artefacts could also be due to emphysematous GB. In this case, check the liver for hyperechoic locules in the portal venous system. 

SONOGRAPHIC MURPHEY'S

Sonographic Murphey's is when the patient complains of maximal pain when the abdomen is gently pressed with the US transducer while imaging the GB. To get the most accurate response, make sure the GB is in the middle of the screen when performing the test. 

Emphysematous GB causing GB necrosis is non tender to palpation: in this case, the patient would be septic and unwell. 

PERICHOLECYSTIC FLUID

Pericholecystic fluid is often seen with GB perforation and localised inflammation. You will see a small localised anechoic area or a rim of anechoic fluid around the GB, 

GB long: thickened wall and pericholcystic fluid

In the absence of other features of cholecystitis, the anechoic area could be a benign condition called focal fatty sparing which occurs commonly in fatty liver at the porta hepatis (5). 

BILE DUCTS

CBD dilatation can occur due to intrinsic (wall thickening from inflammation. malignancy, sludge/ stones etc) or extrinsic (pancreatic head mass, porta hepatis mass etc) causes. The normal CBD is <6mm. Age >60 or cholecystectomy could increase this by about 1mm (6). 

Dilated CBD

Without colour, the dilated CBD above the portal vein gives the appearance of a double barrel shot gun.

CBD: dilated: double barrel shotgun appearance

Always have a look at the liver for intraheptic duct dilatation. In 2D, bile ducts are thin walled and have a stellate appearance (7). Also look at the head of pancreas and around the porta hepatis for a mass. In the end further imaging with CT will be required for these patients.

Dilated intraheptic ducts (colour doppler will help distinguish BD from blood vessels. 

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REFERENCES

1. Summers SM, Scruggs W, Menchine MD, Lahham S, Anderson C, Amr O, Lotfipour S, Cusick SS, Fox JC. A prospective evaluation of emergency department bedside ultrasonography for the detection of acute cholecystitis. Ann Emerg Med. 2010 Aug;56(2):114-22

2. Ralls PW, Colletti PM, Lapin SA, Chandrasoma P, Boswell WD Jr, Ngo C, Radin DR, Halls JM. Real-time sonography in suspected acute cholecystitis. Prospective evaluation of primary and secondary signs. Radiology. 1985 Jun;155(3):767-71.

3. Ko CW, Sekijima JH, Lee SP. Biliary sludge. Ann Intern Med. 1999 Feb 16;130(4 Pt 1):301-11.

4. Miyoshi H, Inui K, Katano Y, Tachi Y, Yamamoto S. B-mode ultrasonographic diagnosis in gallbladder wall thickening. J Med Ultrason (2001). 2021 Apr;48(2):175-186

5. Wu S, Tu R, Liu G. Frequency and implication of focal fatty sparing in segmental homogeneous fatty liver at ultrasound. J Med Ultrason (2001). 2013 Oct;40(4):393-8

6. Govindan S, Tamrat NE, Liu ZJ. Effect of Ageing on the Common Bile Duct Diameter. Dig Surg. 2021;38(5-6):368-376.

7. Laing FC, London LA, Filly RA. Ultrasonographic identification of dilated intrahepatic bile ducts and their differentiation from portal venous structures. J Clin Ultrasound. 1978 Apr;6(2):90-4.