Formation Mechanism of Gallbladder Polyps
Gallbladder polyps form through two distinct pathophysiologic mechanisms: nonneoplastic proliferation (primarily cholesterol deposition and inflammatory hyperplasia) or neoplastic transformation of the gallbladder epithelium. 1
Nonneoplastic Polyp Formation
The majority of gallbladder polyps arise through benign, non-cancerous processes:
Cholesterol Polyps (Most Common)
- 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, 2
- These lesions represent focal lipid deposits rather than true neoplastic growth, with negligible malignant potential 1
- They typically remain small (<10mm) and static over time 3
Inflammatory Polyps
- Form secondary to chronic inflammation of the gallbladder mucosa, creating pseudopolypoid projections 4
- These have no malignant potential and are considered pseudopolyps rather than true neoplastic lesions 4
Adenomyomatosis
- Represents mural hyperplasia with proliferation of surface epithelium that invaginates into the gallbladder wall, forming Rokitansky-Aschoff sinuses 5
- Accounts for approximately 25% of polypoid lesions after cholesterol polyps 2
- Can be diffuse, focal, or segmental in distribution 5
Neoplastic Polyp Formation
A small minority (approximately 6%) of gallbladder polyps arise through true neoplastic transformation 1:
Adenomatous Polyps
- Develop through dysplastic transformation of the gallbladder epithelium, similar to the adenoma-carcinoma sequence seen in other gastrointestinal organs 6
- 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
- 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
- Occur in only 0.2%-0.5% of cholecystectomy specimens 7, 1
- May be associated with genetic syndromes including familial adenomatous polyposis or Peutz-Jeghers syndrome 7, 1
Key Distinguishing Features
Neoplastic polyps are typically larger (mean size 18-21mm) compared to nonneoplastic polyps (mean size 4-7.5mm), reflecting their different growth mechanisms 7, 1
Geographic and Genetic Influences
- 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 7
- Potential genetic loci have been identified in North Indian and Japanese populations that may influence neoplastic polyp formation 7