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Gallstones and Sludge

Published on 19/07/2015 by admin

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Last modified 22/04/2025

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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.

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(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.)
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(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.)

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(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 Wall-echo-shadow sign when GB is filled with stones

– Anterior GB wall demarcated by echogenic line (wall), followed by layer of bile demarcated by hypoechoic line (echo), followed by posterior acoustic shadowing from superficial stones (shadow)
– Posterior wall of GB or deeper stones not visible due to acoustic shadowing
image US not sensitive for detection of choledocholithiasis

– Distal CBD often obscured by bowel gas
• Sludge

image Layering material in dependent portion of GB which should shift slowly with repositioning of patient

– Variable echogenicity: May be uniformly echogenic, hypoechoic with punctate hyperechoic foci, or heterogeneous echogenicity

image Hepatization: GB entirely filled with sludge with same echogenicity as liver
– No posterior acoustic shadowing
– Side lobe artifact may mimic sludge
image Can assume rounded or mass-like configuration (tumefactive sludge)

– Unlike intraluminal mass, no vascularity on Doppler US and should be mobile when patient is repositioned
– Wall of gallbladder should be intact (unlike cancer)

Fluoroscopic Findings

• Oral cholecystography

image > 90% sensitivity and specificity when GB is visualized

– GB nonvisualization occurs in 25% (nonspecific finding)
image Complementary to US when GB cannot be identified ultrasonographically (i.e., GB is contracted or full of stones)
image Better determination of number and size of stones and cystic duct patency

DIFFERENTIAL DIAGNOSIS

GB Cholesterol Polyp

• Focal form of cholesterolosis
• Immobile nodule associated with comet-tail artifact

GB Intraluminal Polyp

• Immobile nodule with internal color flow vascularity
• Cholesterol polyps may demonstrate “comet tail” artifact

GB Adenomyomatosis

• Segmental thickening or cystic mass at GB fundus
• No posterior acoustic shadowing, but often associated with tiny echogenic foci that demonstrate “comet tail” artifact

GB Carcinoma

• Immobile mass in GB with internal color flow vascularity
• May fill GB (making identification of GB difficult) and can extend through GB wall to involve adjacent organs
• 75% of patients with GB cancer have associated gallstones
• Often associated with large, bulky porta hepatis lymph nodes

GB Metastases

• Melanoma most common metastasis to gallbladder
• Soft tissue mass with internal color flow vascularity
• Usually less local invasion than with GB carcinoma

Emphysematous Cholecystitis

• Echogenic reflectors (gas) with dense posterior acoustic shadowing which may mimic a GB filled with stones
• “Dirty” acoustic shadowing, ring-down artifact, and lack of wall-echo-shadow complex suggest correct diagnosis

Porcelain Gallbladder

• Echogenic curvilinear structure in gallbladder fossa with dense posterior acoustic shadowing
• No wall-echo-shadow complex and posterior wall of GB may be visualized (unlike stones filling GB)

PATHOLOGY

General Features

• Etiology

image Cholesterol stones

– Bile supersaturation → GB mucosal inflammation → procrystalizing proteins secretion → crystallization → stone growth

image Risk factors: ↑ age, obesity, rapid weight loss, pregnancy, female, slow intestinal transit, ileal disease, high-fat diet, medication (e.g., clofibrate)
– ↓ GB motility increases rate of crystallization and stone growth

image Risk factors for decreased motility: Pregnancy, oral contraceptives, TPN, octreotide, rapid weight loss
image Pigment stones

– Black stone: ↑ unconjugated bilirubin, normal cholesterol concentration, altered pH (due to mucosal inflammation)

image Associated with chronic hemolysis, cirrhosis, TPN
– Brown stone: Infection leads to release of bacterial β-glucuronidases, which hydrolyze bilirubin glucuronides and form calcium bilirubinate solution

image Usually seen in malnourished Asian subpopulations (recurrent pyogenic cholangitis)
image Associated with cholestasis and biliary infections
image Sludge

– Composed of various proportions of cholesterol monohydrate crystals, calcium bilirubinate, and mucus

image Sludge composed primarily of cholesterol crystals will not be evident on CT
– Similar pathogenesis to biliary stones
– Associated with rapid weight loss, pregnancy, fasting, TPN, critical illnesses, medications (e.g., ceftriaxone)
• Genetics

image 1st-degree relatives are at ↑ risk of developing symptomatic gallstone disease

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Most patients with gallstones/sludge are asymptomatic
image Biliary colic: Dull aching pain in right upper quadrant with radiation to back or right shoulder

– May be triggered by eating (especially fatty foods), but does not have to be postprandial
– May be associated with nausea and vomiting
– Caused by GB contracting against stone temporarily lodged within cystic duct or GB neck
– Atypical symptoms can mimic other pathology (e.g., chest pain)
– No fever or jaundice; normal lab tests (AST/ALT, alkaline phosphatase, WBC, etc.)

image Abnormalities in these markers suggests complications
• Other signs/symptoms

image  

Demographics

• Age

image Prevalence increases with age
image Gallstones rare in children (usually hemolytic disorder)
image Gallstone ileus most common in debilitated, elderly patients (average age 70)
• Gender

image 2-3x more common in women

– Gap between men and women in incidence of gallstones most evident in younger age groups
• Ethnicity

image Native Americans (Pima Indian) and Scandinavians have ↑ risk of cholesterol gallstones
image Asian populations have ↑ risk of pigment stones
image African Americans may have lower incidence of gallstones
• Epidemiology

image Gallstone prevalence: 10-15% of adult population in USA

– 6-20% incidence world-wide
– 75-80% cholesterol type, 20-25% pigment type
image Most common stone in cirrhotic patients is black (pigment) stone (50-70%)
image Major risk factors for gallstones: Age, female gender, pregnancy, obesity (or rapid weight loss), oral contraceptives, and certain medications
image Incidence of gallstones ↑ with certain diseases: Crohn disease, cirrhosis, hemolytic disorders

Natural History & Prognosis

• Gallstone symptoms resolve completely in > 50%
• Sludge progresses to gallstones in 15%
• Common complications

image Risk of complications ∼ 1% per year
image Acute cholecystitis (36%), acute pancreatitis (gallstones cause 30% of acute pancreatitis), choledocholithiasis (3%), GB cancer or cholangiocarcinoma (0.3%)
• Rare complications

image Biliary-enteric fistula: Untreated gallstones that erode into bowel; most often cholecystoduodenal fistulas
image Gallstone ileus: Migration of stone into bowel through fistula with obstruction of bowel at distal ileum

– Rigler triad present in only 1/3 of cases: Small bowel obstruction, pneumobilia, and stone in GI tract
image Bouveret syndrome: Gastric outlet obstruction due to stone in duodenum or distal stomach
image Dropped gallstones: Gallstones spilled into abdomen during laparoscopic cholecystectomy

– May be asymptomatic or serve as nidus for infection

Treatment

• Gallstones

image No treatment for patients who are asymptomatic
image Surgical treatment is 1st option: Cholecystectomy (open or laparoscopic), ERCP (for choledocholithiasis)

– Cholecystectomy does not resolve symptoms of biliary colic in ∼ 10% of patients
image Medical treatment in patients not considered surgical candidates: Dissolution therapy with oral bile acids or extracorporeal shock-wave lithotripsy
• Sludge

image No treatment for patients who are asymptomatic
image Cholecystectomy (open or laparoscopic) if symptomatic
image Percutaneous cholecystostomy for acalculous cholecystitis in patients who are poor surgical candidates
image
(Left) Transverse US shows a wall-echo-shadow complex caused by stones filling the GB. The “wall” is the outer echogenic stripe image delineating the GB wall, the “echo” is the hypoechoic stripe created by a thin layer of bile image, and the “shadow” is the posterior acoustic shadowing image behind a superficial layer of stones.

image
(Right) US shows multiple echogenic stones image in the CBD. The stones are associated with posterior acoustic shadowing image and cause mild CBD dilatation image.
image
(Left) Coronal volume-rendered CECT demonstrates a stone image in the distal CBD resulting in mild upstream CBD dilatation. CT is only 80% sensitive for gallstones, although identification of stones in the CBD is easier when causing biliary obstruction.

image
(Right) ERCP image in the same patient demonstrates the stone as a well-defined, faceted filling defect image in the CBD.
image
(Left) Axial CECT shows gas image with a “Mercedes-Benz” shape within a large gallstone. The gas itself is of no diagnostic significance and is not a sign of infection. This patient has cholecystitis, evidenced by GB wall thickening image.

image
(Right) Frontal abdominal radiograph shows a GB filled with innumerable opaque calculi image. Calcium bilirubinate stones are typically multiple, small, and radiopaque. A feeding tube image marks the 2nd portion of the duodenum.
image
(Left) Frontal radiograph shows a ring-shaped or “eggshell” calcification image in the right upper quadrant, a typical appearance for a large gallstone.

image
(Right) Axial T2WI MR in the same patient demonstrates a large, hypointense stone image (with some linear higher signal within the stone) in the proximal common duct near the confluence of the ducts. Stones are typically hypointense on T1WI & T2WI, but as in this case, can be have somewhat heterogeneous signal with areas of higher signal within the stone.
image
(Left) Coronal MRCP MIP reconstruction in the same patient demonstrates that the large stone image, visible as a large, hypointense filling defect in the proximal common duct, is causing significant biliary obstruction.

image
(Right) MRCP shows 2 gallstones image within the GB, but normal bile ducts. This patient had a CT scan on which these stones were not visible, since cholesterol stones are often isodense to bile.
image
(Left) Axial T2 FS MR demonstrates a low signal filling defect image in the distal CBD, the characteristic appearance of a stone on MR.

image
(Right) Coronal CECT demonstrates dilated small bowel image, a calcified stone image at the site of transition, and pneumobilia image, the classic Rigler triad of findings associated with gallstone ileus. Gallstones typically enter the bowel through a cholecystoduodenal fistula.
image
(Left) Axial NECT in a patient who had undergone prior cholecystectomy demonstrates a dropped calcified gallstone image in the hepatorenal fossa. Dropped gallstones can be asymptomatic or serve as the nidus for future infection.

image
(Right) Ultrasound demonstrates a typical appearance of sludge image, with hypoechoic material layering within the GB. Notice the lack of posterior acoustic shadowing, unlike the gallstone image also seen in the GB.
image
(Left) Sagittal ultrasound demonstrates material of mixed echogenicity filling the GB lumen, an appearance consistent with sludge.

image
(Right) Sagittal ultrasound demonstrates echogenic sludge filling the GB lumen. Sludge can vary greatly in its appearance, ranging from hypoechoic to hyperechoic.
image
(Left) Sagittal ultrasound demonstrates an echogenic mass image in the GB. Notice that bile outlines the entirety of the mass without a clear attachment to the wall, and there is no acoustic shadowing.

image
(Right) Sagittal color Doppler ultrasound in the same patient shows no vascularity within the mass image. The mass was noted to be mobile when the patient was repositioned. These are characteristic features of tumefactive sludge, which should not be confused with malignancy.
image
Axial CECT shows cholesterol gallstones image that are isodense to bile except for surface “eggshell” calcification that makes them visible.

image
Plain radiography shows “eggshell” calcifications image in the right upper quadrant. CT (not shown) confirmed that these are cholesterol gallstones.
image
Sagittal ultrasound shows multiple gallstones image and a poorly defined GB wall image. A gangrenous GB was also demonstrated on a subsequent CT scan and resected at surgery.
image
Sagittal ultrasound shows amorphous echogenic material image within the GB that moves with changes in position, findings typical of sludge.
image
Sagittal oblique ultrasound shows amorphous echogenic material within the GB that moves with changes in position. The findings are typical of sludge.
image
Axial CECT demonstrates a lamellated, calcified gallstone image causing proximal bowel obstruction, a so-called gallstone ileus.
image
Coronal CECT demonstrates a soft tissue density stone image in the CBD. Stones can be quite difficult to appreciate on CT when they are not calcified.
image
Ultrasound shows multiple asymptomatic gallstones image with posterior acoustic shadowing image. The gallbladder wall is normal image. (Courtesy B. Paunipagar, MD.)
image
Ultrasound shows multiple incidental gallstones image with posterior acoustic shadowing image. The GB wall is not thickened image (Courtesy of B. Paunipagar, MD.)

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