Gallbladder polyps are frequently encountered on cross-sectional imaging, often in asymptomatic patients. Most are benign and of little clinical importance. However, some polyps do have a malignant potential. This article discusses the clinical presentation, diagnosis, and natural history of gallbladder polyps and risk factors for malignant polyps and indications for cholecystectomy.
The increasing use and constantly improving resolution of abdominal imaging modalities in clinical practice often lead to “abnormal” findings that are of unclear significance. Polypoid lesions of the gallbladder are a prime example of this, as they are frequently diagnosed on routine transabdominal ultrasounds. Any projection of mucosa into the lumen of the gallbladder is defined as a polypoid lesion of the gallbladder, regardless of the neoplastic potential. Many gallbladder polyps are often diagnosed incidentally following cholecystectomy for gallstones or biliary colic. The estimated prevalence of gallbladder polyps varies by the demographics of the studied population, but it is generally considered to be around 5%. The vast majority of gallbladder polyps are benign, and gallbladder cancer is a very rare disease. The estimated new cases of gallbladder and other biliary cancers only represented 0.66% of the estimated new cancer cases in the United States in 2009, accounting for only 0.60% of estimated new cancer deaths. This article discusses the clinical presentation, diagnosis, and natural history of gallbladder polyps, as well as risk factors for malignant polyps and indications for cholecystectomy.
Classification
A classification of benign tumors and pseudotumors of the gallbladder was first proposed in 1970. Benign tumors include adenomas, lipomas, hemangiomas, and leiomyomas. Benign pseuodotumors include adenomyomas, cholesterol polyps, inflammatory polyps, and heterotopic mucosa from the stomach, pancreas, or liver. The current accepted classification divides these polyps into neoplastic (adenomas, carcinoma in situ) and non-neoplastic, with the non-neoplastic polyps accounting for about 95% of these lesions.
The most common of the non-neoplastic polyps is the cholesterol polyp. These result when the lamina propria is infiltrated with lipid-laden foamy macrophages. Cholesterol polyps account for about 60% of all gallbladder polyps and are generally less than10 mm. Often, multiple cholesterol polyps are present. Adenomyomatosis of the gallbladder is a benign, hyperplastic lesion caused by excessive proliferation of surface epithelium, which can then invaginate into the muscularis. Adenomyomatosis accounts for about 25% of gallbladder polyps and usually localizes to the gallbladder fundus appearing as a solitary polyp ranging in size from 10 to 20 mm. Adenomyomatosis is not considered neoplastic. Inflammatory polyps account for about 10% of gallbladder polyps and result from granulation and fibrous tissue secondary to chronic inflammation. They are typically less than 10 mm in size and are not neoplastic.
Adenomas account for about 4% of gallbladder polyps and are considered neoplastic. They range in size from 5 to 20 mm, are generally solitary, and are often associated with gallstones. Whether or not gallbladder adenomas progress to adenocarcinomas is not clear. Several studies do support this potential progression. Kozuka and colleagues analyzed 1605 cholecystectomy specimens and found histological, traceable transitions from the 11 benign adenomas, 7 adenomas with malignancy changes, and 79 invasive carcinomas. Other case reports support this adenoma-to-cancer progression. However, this progression is not felt to be the predominant pathway of carcinogenesis in the gallbladder, and K-ras mutations have not been detected in gallbladder carcinomas associated with an adenoma.
Finally, rare miscellaneous neoplastic polyps of varying sizes account for the remaining 1% of gallbladder polyps and include leiomyomas, lipomas, neurofibromas, and carcinoids.
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