Formation Mechanism of Gallbladder Polyps

Nonneoplastic Polyp Formation

Cholesterol polyps account for approximately 60% of all gallbladder polyps and form when cholesterol-laden macrophages accumulate in the lamina propria of the gallbladder mucosa 1
These lesions represent focal lipid deposits rather than true neoplastic growth, with negligible malignant potential 1
Adenomyomatosis represents mural hyperplasia with proliferation of surface epithelium that invaginates into the gallbladder wall, forming Rokitansky-Aschoff sinuses 2
Adenomyomatosis can be diffuse, focal, or segmental in distribution 2

A small minority (approximately 6%) of gallbladder polyps arise through true neoplastic transformation 1
Intracholecystic papillary neoplasms (ICPNs) are mass-forming, noninvasive epithelial neoplasms ≥10mm that project into the gallbladder lumen with four morphologic patterns: biliary, gastric, intestinal, and oncocytic 1
ICPNs may exhibit low-grade or high-grade epithelial dysplasia 1
Pyloric gland adenomas form as smooth-surfaced polypoid lesions composed of tightly packed glands with pyloric-type low cuboidal epithelium 1
Pyloric gland adenomas occur in only 0.2%-0.5% of cholecystectomy specimens 3, 1
Pyloric gland adenomas may be associated with genetic syndromes including familial adenomatous polyposis or Peutz-Jeghers syndrome 3, 1

Neoplastic polyps are typically larger (mean size 18-21mm) compared to nonneoplastic polyps (mean size 4-7.5mm), reflecting their different growth mechanisms 3, 1
Primary sclerosing cholangitis is associated with gallbladder polyp development secondary to a biliary epithelium field defect, with significantly higher rates of malignant transformation (18%-50%) 3, 1

The highest incidences of gallbladder carcinoma (which may manifest as polyps) occur in North and South American Indigenous populations and North Indian populations, suggesting underlying genetic and environmental factors in neoplastic transformation 3
Potential genetic loci have been identified in North Indian and Japanese populations that may influence neoplastic polyp formation 3