Normal Gallbladder Imaging Appearance
A normal gallbladder on ultrasound appears as an anechoic (fluid-filled) pear-shaped structure with a thin, echogenic wall measuring ≤3 mm in thickness, typically measuring up to 10 cm in length and 4 cm in width, with no stones, pericholecystic fluid, or wall irregularity 1.
Ultrasound Appearance
Wall Characteristics
- Wall thickness: ≤3 mm when measured on the anterior wall (between lumen and hepatic parenchyma) 1
- Wall structure: Single echogenic layer with normal trilaminar architecture 1
- Wall appearance: Smooth, regular contour without irregularity or heterogeneous echogenicity 1
Size Parameters
- Length: Up to 7.5 cm in children 2; can reach >10 cm in adults, especially with increasing age 3
- Transverse diameter: Typically <5 cm (diameters >5 cm suggest pathology like cholecystitis) 1
- Micro-gallbladders: Maximal diameters <3.5 cm are considered small 3
Important caveat: Gallbladder size is highly variable and influenced by age, fasting state, diabetes, and obesity. Post-prandial states cause physiologic wall thickening that should not be mistaken for pathology 1, 3.
Lumen Characteristics
- Contents: Anechoic (echo-free) bile without echogenic material
- No stones: Absence of mobile echogenic structures with posterior acoustic shadowing 1
- No sludge or debris: Clear lumen without layering material
Surrounding Structures
- No pericholecystic fluid: Absence of hypoechoic or anechoic collections around the gallbladder 1
- Common bile duct (CBD): Normal intraluminal diameter ≤3-4 mm, though may increase by 1 mm per decade of age 1
CT Appearance
On CT with IV contrast, a normal gallbladder appears as a thin-walled fluid-density structure without wall thickening, pericholecystic inflammation, or adjacent liver parenchymal hyperemia 4.
Key CT Features
- Wall enhancement: Minimal, uniform enhancement without abnormal thickening
- Adjacent liver: No hyperemia or inflammatory changes in adjacent hepatic parenchyma 4
- Pericholecystic region: No inflammatory stranding or fluid collections 4
- Stones: CT has only ~75% sensitivity for gallstones (calcified stones are readily visible; cholesterol stones may appear less dense than bile) 4
Critical limitation: CT without IV contrast cannot assess wall enhancement or adjacent liver hyperemia, which are important early findings in pathology 4.
MRI/MRCP Appearance
On MRI, a normal gallbladder demonstrates thin walls with low T2 signal intensity, fluid-filled lumen with high T2 signal, and no ductal dilatation or filling defects on MRCP sequences 4.
MRI Signal Characteristics
T2-weighted imaging:
Contrast-enhanced sequences: Minimal, uniform wall enhancement without perihepatic enhancement 4
MRCP Features
- Biliary tree visualization: Normal caliber bile ducts without dilatation or filling defects
- Cystic duct: Patent and visible (advantage over ultrasound) 4
- CBD: Normal diameter without stones or strictures
- Sensitivity: 85-100% for cholelithiasis/choledocholithiasis 4
Key advantage: MRI/MRCP superior to both ultrasound and CT for visualizing the cystic duct, CBD, and distinguishing acute from chronic pathology based on wall signal characteristics 4.
Common Pitfalls to Avoid
- Posterior wall measurement: Avoid measuring posterior wall thickness due to adjacent bowel loops; always measure the anterior wall against hepatic parenchyma 1
- Post-prandial scanning: Physiologic wall thickening after eating mimics pathology 1
- Age-related CBD dilatation: CBD up to 6-7 mm may be normal in elderly patients (1 mm per decade rule) 1
- Bowel gas artifact: Can mimic stones or obscure the gallbladder fundus; reposition patient or use decubitus views 1
- Non-biliary wall thickening: Hypoproteinemia and congestive heart failure cause wall thickening without cholecystitis 1