Gallbladder polyps are common abnormal growths that form on the inner mucosal lining of the gallbladder wall. These projections are typically discovered incidentally during an abdominal ultrasound or other imaging tests performed for unrelated reasons. Most individuals with gallbladder polyps experience no symptoms. While the majority of these growths are benign, a small percentage can carry the potential for malignant change, which necessitates careful medical attention. The ultimate outcome for a gallbladder polyp—whether it remains stable, grows, or disappears—is largely dependent on its underlying cellular makeup.
Understanding Gallbladder Polyp Types
Gallbladder polyps are broadly categorized into two main groups: non-neoplastic and neoplastic, a distinction that determines their biological behavior. Non-neoplastic polyps, which are not true tumors, represent the vast majority of findings, accounting for 90% or more of all cases. The most common subtype is the cholesterol polyp, which makes up 60% to 90% of all gallbladder polyps. These are not growths of abnormal tissue but rather accumulations of cholesterol lipids that have deposited and adhered to the gallbladder lining, a condition known as cholesterolosis.
Other non-neoplastic types include inflammatory polyps, which are composed of granulation and scar tissue resulting from chronic inflammation or irritation of the gallbladder wall. Adenomyomatosis is another non-neoplastic form, characterized by an overgrowth of the inner lining and thickening of the muscular layer of the gallbladder wall, often forming small cysts. Since these non-neoplastic lesions are not composed of abnormally dividing cells, they carry virtually no potential for becoming cancerous.
In contrast, neoplastic polyps, such as adenomas, are true benign tumors considered premalignant lesions. These epithelial growths are composed of cells that resemble the lining of the biliary tract and have the potential to progress toward malignancy. While they are far less common than cholesterol polyps, their presence requires a cautious management approach due to this potential for cancerous transformation.
Factors Influencing Polyp Regression
Whether a gallbladder polyp can disappear on its own is determined by the polyp’s specific type and its size. Regression, or spontaneous disappearance, is almost exclusively observed in non-neoplastic polyps, particularly the common cholesterol type. The mechanism is tied to their composition; since they are cholesterol deposits rather than true tissue growths, they may detach or be reabsorbed if lipid metabolism improves. This reabsorption or shedding is most likely to occur in polyps measuring 5 millimeters or less in diameter.
Some studies have documented the total disappearance of small gallbladder polyps during follow-up. A significant decrease in size, often defined as a reduction of 4 millimeters or more, is generally considered equivalent to regression and a sign of a benign course. While changes in diet and cholesterol levels are theoretically linked to the formation and potential regression of cholesterol polyps, there is no direct evidence that cholesterol-lowering medication reliably shrinks these growths.
The natural history of neoplastic polyps, such as adenomas, is different from that of cholesterol deposits. These growths are formed from abnormal cell proliferation and therefore do not regress spontaneously. Once a neoplastic polyp forms, it will either remain stable or increase in size, making size change a critical factor in determining malignancy risk.
When Polyps Require Monitoring or Intervention
Because polyps carry a small but real risk of harboring or developing cancer, a “wait-and-see” strategy with regular monitoring is applied to most small, asymptomatic polyps. For polyps measuring 5 millimeters or less in a patient without additional risk factors, guidelines recommend no further follow-up is necessary due to the extremely low malignancy risk. Surveillance with follow-up ultrasound is initiated for polyps between 6 and 9 millimeters, with examinations scheduled at intervals (e.g., six months, one year, and two years).
Intervention (cholecystectomy) becomes the recommended course when the risk of malignancy outweighs the risk of surgery. The primary size threshold for surgical consultation is 10 millimeters, as the average size of neoplastic polyps is significantly larger than non-neoplastic types. Any polyp that grows rapidly, defined as an increase of 4 millimeters or more within a single year, is an urgent indication for intervention, regardless of its initial size.
Patient-specific risk factors can lower the size threshold for recommending cholecystectomy, even for polyps in the 6-to-9-millimeter range. These factors include age over 60 years, the presence of primary sclerosing cholangitis, or a polyp exhibiting a sessile (broad-based, flat) morphology rather than a stalked (pedunculated) one. In these higher-risk scenarios, surgical removal is advised because the chance of an underlying malignancy is significantly elevated.