Polyp size of 1 cm is insufficient to discriminate neoplastic and non-neoplastic gallbladder polyps

BACKGROUND: A significant proportion of gallbladder polyps are non-neoplastic, for which resection is not necessary. However, international guidelines advocate cholecystectomy for all polyps ≥ 1 cm. This study assessed a national cohort of histopathologically proven gallbladder polyps to distinguish neoplastic from non-neoplastic polyps. METHODS: PALGA, the nationwide network and registry of histo- and cytopathology, was searched to identify all histopathologically proven gallbladder polyps between 2003 and 2013. All polyps and (focal) wall thickenings > 5 mm were included, and classified as neoplastic or non-neoplastic. Polyp subtype, size, distribution, presentation as wall thickening or protruding polyp, and presence of gallstones were assessed for neoplastic and non-neoplastic polyps. A decision tree to distinguish neoplastic and non-neoplastic polyps was made and diagnostic accuracy of 1 cm surgical threshold was calculated. RESULTS: A total of 2085 out of 220,612 cholecystectomies contained a polyp (0.9%). Of these polyps, 56.4% were neoplastic (40.1% premalignant, 59.9% malignant) and 43.6% non-neoplastic (41.5% cholesterol polyp, 37.0% adenomyomatosis, 21.5% other). Polyp size, distribution, and presence of gallstones were reported in 1059, 1739 and 1143 pathology reports, respectively. Neoplastic polyps differed from non-neoplastic polyps in size (18.1 mm vs 7.5 mm, p < 0.001), singularity (88.2% vs 68.2%, p < 0.001), wall thickening (29.1% vs 15.6%, p < 0.001), and presence of gallstones (50.1% vs 40.4%, p = 0.001). However, adenomyomatosis presented with similar characteristics as neoplastic polyps. Fifty percent of polyps were ≥ 1 cm surgical threshold (optimal surgical threshold based on ROC-curve); sensitivity for indicating neoplastic polyps was 68.1%, specificity was 70.2%, and positive and negative predictive values were 72.9% and 65.1%. CONCLUSIONS: The prevalence of gallbladder polyps on cholecystectomy is low and many of the polyps are non-neoplastic. Clinicopathological characteristics differ between neoplastic and non-neoplastic polyps in general, but these cannot properly indicate neoplasia. The 1 cm surgical threshold has moderate diagnostic accuracy and is insufficient to indicate surgery for neoplastic gallbladder polyps.