Gallstones and Sludge

Published on 19/07/2015 by admin

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Last modified 19/07/2015

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 Choledocholithiasis: Stones within common bile duct (CBD)

• Sludge: Suspension of particulate material/bile in gallbladder (GB)

IMAGING

• Gallstones

image Ultrasound: Brightly echogenic nodule with marked posterior acoustic shadowing

– Mobile with “twinkling” on color Doppler images
– Wall-echo-shadow sign when GB is filled with stones

image Anterior wall of GB is demarcated by echogenic line (“wall”), deep to which is a layer of bile demarcated by hypoechoic line (“echo”), followed by posterior acoustic shadowing from most superficial stones (“echo”)
image MR: Stones most conspicuous on T2WI and MRCP

– Usually low signal (signal void) on T1WI and T2WI
– MRCP better than CT/US for CBD stones
image CT: Overall sensitivity of CT for stones is roughly 80%

– 20% of stones are not identified on CT, often “pure” cholesterol stones, which are isodense to bile
image Radiographs: Only 10-20% of cholesterol stones are visible on radiographs
• Sludge

image Layering, mobile material in dependent portion of GB
image Variable echogenicity with no acoustic shadowing
image May have mass-like appearance (tumefactive sludge)

– No vascularity on Doppler US and should be mobile

TOP DIFFERENTIAL DIAGNOSES

• GB intraluminal polyp or cholesterol polyp, GB carcinoma, GB adenomyomatosis, emphysematous cholecystitis, porcelain GB

CLINICAL ISSUES

• Gallstones associated with older age, female gender, pregnancy, obesity, rapid weight loss, and medications
• Sludge associated with rapid weight loss, pregnancy, fasting, TPN, critical illnesses, and some medications
• Gallstones/sludge usually asymptomatic,  but can be associated with biliary colic and numerous complications
image
(Left) Coronal illustration shows cholelithiasis image and choledocholithiasis image. While most gallstones are asymptomatic, migration of stones to the cystic duct and common bile duct (CBD) may cause numerous complications, including biliary colic, cholecystitis, biliary obstruction, and pancreatitis.

image
(Right) Gross photograph shows a gallbladder (GB) filled with numerous smooth, yellow cholesterol stones. The GB wall is mildly thickened and hyperemic. (Courtesy G. F. Gray, MD.)
image
(Left) Gross photograph shows numerous faceted black pigment stones distending the GB lumen. The GB wall is thickened and edematous. (Courtesy G. F. Gray, MD.)

image
(Right) Grayscale ultrasound of the GB shows a typical echogenic stone image within the GB lumen. Note the presence of posterior acoustic shadowing image. The GB wall thickness is normal and there is no pericholecystic fluid to suggest cholecystitis.

TERMINOLOGY

Synonyms

• Gallstones: Biliary stone, cholelithiasis, choledocholithiasis
• Sludge: Biliary sludge, microlithiasis, biliary sand, pseudolithiasis, microcrystalline disease

Definitions

• Gallstones: Concretions within biliary system (gallbladder [GB] and biliary ducts)

image Cholesterol stone (75-80%): Cholesterol is main constituent
image Pigment stone (20-25%): Calcium-bilirubinate is main constituent

– Black stone: Usually pigment stone in sterile GB; small and tar-like stones frequently associated with cirrhosis and hemolytic states
– Brown stone: Usually pigment stone in infected bile duct, associated with cholestasis and biliary infections (e.g., recurrent pyogenic cholangitis)
• Choledocholithiasis: Stones in common bile duct (CBD)
• Sludge: Suspension of particulate material/bile in GB

IMAGING

General Features

• Best diagnostic clue

image Gallstone: Mobile, brightly echogenic mass in GB with marked posterior acoustic shadowing
image Sludge: Mobile low-level echoes layering in dependent portion of GB with no acoustic shadowing
• Location

image Cholesterol and black stones form within GB
image Brown stones form within bile ducts
image Small stones (either cholesterol or pigment) may pass into CBD
image Stones usually found in dependent portion of GB
• Size

image Cholesterol stones are often multiple and range up to several centimeters in diameter
image Black stones are usually numerous and < 1.5 cm
image Can fill GB with innumerable stones or 1 large stone
• Morphology

image Surfaces of stones may be round or faceted
image Rim calcification: Adsorbed rings of calcium in and on stone

Imaging Recommendations

• Best imaging tool

image Ultrasound best for identifying GB stones
image ERCP and MRCP superior for bile duct stones
• Protocol advice

image Ultrasound harmonic imaging decreases side lobe, near field reverberation artifact

Radiographic Findings

• Only 10-20% of cholesterol stones have enough calcium to be visible on plain films

image 50-75% of black stones are radiopaque
image Majority of brown stones are radiolucent
• Mercedes-Benz sign: Gas within central fissures of stones

image Does not imply infection or complication

CT Findings

• No evidence that NECT improves visualization of stones
• Overall sensitivity of CT for stones is roughly 80%

image 20% of stones are not identified on CT, often “pure” cholesterol stones which are isodense to bile
image Common duct stones difficult to perceive if located within nondilated duct
image Higher kVp settings may improve stone visualization
• Single or multiple filling defects in GB or ducts

image Density varies: Calcium density, soft tissue density, or lucent (pure cholesterol or gas-containing)
image Pattern of calcification: Uniformly calcified, laminated, rim calcification, or central nidus of calcification
image If stones not seen, “meniscus” configuration of distal CBD (with proximal dilatation) suggests occult stone
image May be gas within stones on CT (Mercedes-Benz sign)
• Most helpful for assessing complications of gallstones, such as cholecystitis or gallstone ileus
• Sludge: Nonenhancing layering material with attenuation ≥ bile

image Often not evident on CT (US is more sensitive)

MR Findings

• Stones most conspicuous on T2WI and MRCP
• Usually low signal (signal void) on T1WI and T2WI

image May rarely show central hyperintensity on T1WI or T2WI due to presence of proteins within stones
image May rarely have high T2 signal (bile within stone)
image Pigment stones may sometimes show T1WI hyperintensity and are more variable in signal (on any sequence) compared to cholesterol stones
• MRCP superior to US or CT for identification of CBD stones

image Accuracy probably equivalent to ERCP

Ultrasonographic Findings

• Gallstones

image Ultrasound very sensitive (95%) and specific (95%) for stones > 2 mm
image Brightly echogenic nodule in GB with marked posterior acoustic shadowing

– Small stones may not shadow
– Stones should be mobile when repositioning patient
– May show “twinkling” artifact on color Doppler images
image 

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