INTRODUCTION

Gallbladder polyps are outgrowths of the gallbladder mucosal wall. They are usually found incidentally on ultrasonography or after cholecystectomy. When detected on ultrasonography, their clinical significance relates largely to their malignant potential. The majority of these lesions are not neoplastic but are hyperplastic or represent lipid deposits (cholesterolosis). On the other hand, imaging studies alone are insufficiently specific to exclude the possibility of gallbladder carcinoma or premalignant adenomas. Furthermore, even benign lesions can occasionally lead to symptoms similar to those caused by gallbladder stones.

While the widespread use of ultrasonography has made the diagnosis of polypoid lesions of the gallbladder increasingly frequent, optimal strategies for evaluating these lesions have not been established. This topic will review the clinical significance and differential diagnosis of gallbladder polyps, and will provide a practical approach to their management. Gallbladder cancer is discussed in detail elsewhere. (See "Gallbladder cancer: Epidemiology, risk factors, clinical features, and diagnosis".)

EPIDEMIOLOGY

Gallbladder polyps have been observed in 0.004 to 13.8 percent of resected gallbladders [1], and in 1.5 to 4.5 percent of gallbladders assessed by ultrasonography [2,3]. In one report, no association was observed between the presence of polyps and the patient's age, sex, weight, number of pregnancies, use of exogenous female hormones, or any other risk factors that are generally believed to be associated with gallstones [3]. Gallbladder polyps have only rarely been described in children, in whom they occur either as a primary disorder or in association with other disorders, including metachromatic leukodystrophy, Peutz-Jeghers syndrome, or pancreatobiliary malunion [4]. (See "Epidemiology of and risk factors for gallstones".)

CLASSIFICATION

The classification of gallbladder polyps was first proposed in 1970 based upon a review of 180 benign tumors [5]. As a general rule, polypoid lesions can be categorized as benign or malignant (table 1) [6,7]. Benign lesions have been further subdivided into neoplastic or non-neoplastic:

• The most common benign neoplastic lesion is an adenoma. Benign mesodermal tumors such as leiomyomas and lipomas are rare.
• The most common benign non-neoplastic lesions (pseudotumors) are cholesterol polyps (the presence of which is referred to as "cholesterolosis"), followed by adenomyomas (the presence of which is referred to as "adenomyomatosis"), and inflammatory polyps [1,5]. Cholesterolosis and adenomyomatosis are mucosal abnormalities of the gallbladder. They have been referred to as "hyperplastic cholecystoses", a term introduced in 1960 to differentiate them from inflammatory conditions such as acute cholecystitis, since they lack inflammatory features but exhibit features of hyperplasia [8]. However, some data suggest that adenomyomatosis may be associated with an increased risk of gallbladder cancer. (See 'Adenomyomatosis' below.)
• The most common malignant lesion in the gallbladder is adenocarcinoma. Gallbladder adenocarcinomas are much more common than gallbladder adenomas, in contrast to the colon where adenomas are much more common than adenocarcinomas. Squamous cell carcinomas, mucinous cystadenomas, and adenoacanthomas of the gallbladder are rare.