Effect of gallbladder polyp size on the prediction and detection of gallbladder cancer

Background: Gallbladder polyps are relatively common. Although most gallbladder polyps are benign, some are malignant. Current guidelines state that malignancy should be suspected for polyps ≥ 10 mm in diameter. We clarified the cancer detection rates in accordance with the size distribution of gallbladder polyps, and evaluated the effectiveness of the reported risk factors in predicting malignancy.

Methods: In this retrospective case-control study, our institutional database was searched to identify patients who underwent laparoscopic cholecystectomy for benign or malignant gallbladder polyps at Sada Hospital, Japan. The chi-squared test was used to analyze the risk factors for malignancy.

Results: There were 227 protruding gallbladder lesions. The 206 benign polyps had a diameter of 2-21 mm, while the 21 malignant polyps were 7-60 mm. The cancer detection rates were 16.4% for lesions ≥ 10 mm, 55.9% for lesions ≥ 15 mm, and 94.1% for lesions ≥ 20 mm. Of the benign lesions, cholesterol polyps were the most frequent (50-100%) in all size ranges, even in large lesions (≥ 15 mm). The sessile lesion morphology was significantly more frequent in malignant (60%) than benign lesions (3.4%, p < 0.00001). Multiple polyps were frequently diagnosed not only as cholesterol polyps (81.1%), but also as adenomas (60%); adenomas were found as a single adenoma within other types of polyps. There were two cases of malignant small gallbladder polyps (< 10 mm); these lesions met the surgical indications of a size increase during observation or a sessile morphology.

Conclusions: The cancer detection rate increased significantly with an increase in the lesion size. Risk factors such as a sessile polyp morphology or an increase in lesion size were effective in predicting malignancy for small gallbladder polyps. It might be difficult to accurately predict the pathologic diagnoses of gallbladder polyps preoperatively, as cholesterol polyps were most frequent, even in the large size range.