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

Abstract

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.

Keywords: Cholecystectomy; Gallbladder polyp; Neoplasia; Surgical threshold.

Fig. 1

Flowchart patient identification

Fig. 2

Histopathological subtypes of neoplastic and non-neoplastic polyps. *Consists of: squamous cell carcinoma (n = 13), lymphoma (n = 10), metastasis (n = 9), carcinoïd (n = 5), other neuroendocrine tumor (n = 5), sarcoma (n = 5), papillary carcinoma (n = 4), undifferentiated carcinoma (n = 4), granular cell myoblastoma (n = 2), melanoma (n = 1), colloid carcinoma (n = 1), spindle and giant cell carcinoma (n = 1), small cell carcinoma (n = 1). ^Consists of: hemangioma (n = 4), lipoma (n = 3), lymphangioma (n = 3), fibroma (n = 3), follicular cholecystitis (n = 2), and non-specified polyp (n = 66)

Fig. 3

Surgical threshold. Gallbladder polyps and subgroups above and below surgical threshold of 1 cm. Neoplastic polyps significantly differed from non-neoplastic polyps (p < 0.001). Pre-malignant polyps significantly differed from malignant polyps (p < 0.001). Cholesterol polyps significantly differed from other non-neoplastic polyps (p < 0.001). Adenomyomatosis significantly differed from other non-neoplastic polyps (p < 0.001)

Fig. 4

ROC-curve polyp size. ROC-curve of polyp size compared for neoplastic polyp type. Area under the curve: 0.75 (95% CI 0.72–0.78). Optimal diagnostic cut-off size is 1 cm with sensitivity of 0.68 and specificity of 0.70 (p < 0.001). Sensitivities and specificities for all cut-off values are provided as supplementary table

Fig. 5

Surgical threshold and clinicopathological characteristic decision tree. Presented as characteristic, n (%). Size available for n = 1059, number of polyps and wall thickening for n = 985, presence of gallstones and polyp type n = 574. NP neoplastic polyp, NNP nonneoplastic polyp