Gallstones, also called cholelithiasis, are concretions that occur anywhere within the biliary system, most commonly within the gallbladder.
Gallstones (cholelithiasis) describes stone formation at any point along the biliary tree. Specific names can be given to gallstones depending on their location:
- cholecystolithiasis: gallstones within the gallbladder
- choledocholithiasis: gallstones within the bile ducts
Biliary microlithiasis refers to gallstones less than 3 mm in diameter.
Gallstones occur in ~10% of the population with a predominance in women (F:M = 2:1). The prevalence increases with age in both sexes 3.
Genetics may have an important role in gallstone formation. Several studies have shown an association between age-adjusted prevalence of gallstone, ethnicity 4 and family history of gallstones:
- highest age-adjusted prevalence (~50%): Pima Indians, some North and South American Indians
- intermediate age-adjusted prevalence (up to 20%): Caucasians (20%), and Asian population (5-20%)
- lowest age-adjusted prevalence (≤5%): Africans
Common risk factors for cholesterol gallstones include female sex, middle age, obesity, and positive family history (see 5-F rule).
Gallstones may be symptomatic in only 25% of cases. The most common presentation is right upper quadrant or epigastric abdominal pain or discomfort, especially after a fat-rich meal. Other symptoms include belching, bloating, flatulence, heartburn, and nausea.
Abdominal pain is often referred to shoulder. Patients may demonstrate this radiation to the tip of scapula by placing their hand behind the back and thumb pointing upwards: the "Collins' sign". This may be useful in distinguishing gallstone pain from oesophagitis, gastritis, or duodenal ulcer in ~50% of patients 5.
There are three types of gallstones 3,4,7-10:
- >50% cholesterol contents; form with supersaturation of bile, nucleation and stone growth
- predisposing factors
- diet, sedentary lifestyle, rapid loss of weight, obesity, oral contraceptive pill, total parenteral nutrition (TPN)
- ethnicity, genetic predisposition, older age, female sex
- 20-50% cholesterol content
- predisposing factor: similar to cholesterol stones
pigment stones (10%)
- <20% cholesterol content; high bilirubin content and occur when there is supersaturation of unconjugated bilirubin
- two further subtypes each with their own predisposing factors:
Small gallstones carry a higher risk of causing pancreatitis than larger ones.
Some radiopaque gallstones may be seen on plain film:
- gallstones are radiopaque only in 15-20% of cases 3
- may have a laminated appearance
- may have a faceted outline
- may show a Mercedes-Benz sign: radio-opaque outline with lucent center
Ultrasound is considered the gold standard for detecting gallstones 6:
- grey scale ultrasound
- highly reflective echogenic focus within gallbladder lumen, normally with prominent posterior acoustic shadowing
- gravity dependent movement is often seen with change of patient position (the rolling stone sign)
- color Doppler
- may demonstrate a twinkle artefact and is particularly useful for identification of small stones
Pure cholesterol stones are hypoattenuating to bile and calcified gallstones are hyperattenuating to bile. Some gallstones are isodense to bile and these may not be clearly identified on CT.
- T2: signal void or low signal outlined by markedly hyperintense bile within gallbladder
- MRCP: focus of signal void inside gallbladder
Possible imaging differential considerations in selected situations include
- gallbladder polyp
- echogenic bile (sludge) and tumefactive sludge: non-shadowing
- gallbladder carcinoma
- gallstone acoustic shadowing is prominent with
- larger size stones (usually >3 mm for shadowing)
- higher transducer frequency
- focal zone at the level of gallstone
- a gallbladder full of stones may paradoxically be hard to visualise (wall-echo-shadow sign)
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- galllbladder wall abnormalities
- diffuse gallbladder wall thickening (differential)
- focal gallbladder wall thickening (differential)
- gallbladder polyps
- gallbladder malignancy
- porcelain gallbladder
- gallbladder inflammation
- other gallbladder abnormalities