Gallstone Size: There is No "Normal" Size
Gallstones are pathological structures, not normal anatomical findings, and therefore have no "normal" size—they range from tiny particles (<1 mm) to very large stones (>3 cm). 1, 2
Understanding Gallstone Size Spectrum
The term "normal size" is a misnomer when discussing gallstones, as their presence itself represents disease. However, understanding the size distribution is clinically critical:
Small Gallstones (≤5 mm)
- Small stones (≤5 mm) are common and carry the highest risk of migrating through the cystic duct to cause complications such as acute pancreatitis or obstructive jaundice 3
- Patients with pancreatitis have significantly smaller gallbladder stones compared to those with uncomplicated disease (mean diameter of smallest stones: 3 mm vs 9 mm) 3
- Small cholesterol stones may be less echogenic, can float, and may demonstrate "comet tailing" rather than typical acoustic shadowing, making them easier to miss on ultrasound 2
- Stones in the gallbladder neck may be overlooked or mistaken for lateral cystic shadowing artifact 2
Medium Gallstones (6-20 mm)
- Stones between 6-20 mm represent the most common size range encountered in clinical practice 4, 5
- Stones <6 mm in diameter are best treated with oral bile acids if medical management is chosen 4
- Single stones <30 mm or multiple stones (n<3) are candidates for lithotripsy combined with oral bile acid therapy 4
Large Gallstones (>20 mm)
- Large stones (>2 cm) are rarely amenable to non-surgical dissolution therapies and typically require surgical removal 6, 4
- Larger calculi are more often associated with acute cholecystitis than smaller stones 5
- A 2.7 cm stone, for example, far exceeds the recommended limit for non-surgical therapies and mandates laparoscopic cholecystectomy 6
Clinical Implications by Size
Risk Stratification
- Multivariate analysis identifies small stones as independent risk factors for pancreatitis, along with old age 3
- Between 37-86% of gallstones are cholesterol-rich, 2-27% are pigment stones, and 4-16% are mixed 7
- Most patients (>80%) with gallstones remain asymptomatic throughout their lifetime 7
Diagnostic Accuracy
- Ultrasound has 96% diagnostic accuracy for detecting gallstones and should document number, size, mobility, and acoustic shadowing 2
- Gallstones are defined as solid, shadowing, hyperechoic, nonvascular structures within the gallbladder lumen that are generally mobile 1
- Small stones may be overlooked or mistaken for gas in adjacent bowel loops 2
Common Pitfalls to Avoid
- Do not assume that small stones are less clinically significant—they pose the greatest risk for pancreatitis and bile duct obstruction 3
- Avoid relying solely on a single ultrasound view; scan from multiple directions and reposition the patient to check for stone mobility 2
- Do not confuse gallstones with tumefactive sludge (inspissated bile that has coalesced into a "sludge ball") 1
- Recognize that up to 83% of apparent polyps ≤5 mm are not found at subsequent cholecystectomy, suggesting they may represent adherent stones or sludge 1