Gallbladder polyps and the challenge of distinguishing benign lesions from cancer

Abstract

The challenge in the management of patients with gallbladder polyps is to prevent the development of gallbladder cancer and do no harm by unnecessary surgery or futile follow-up. But in daily practice, many lesions are inaccurately reported and overtreated. The prevalence of gallbladder polyps, depending on the population, ranges from 0.3%–9.5%.1 These percentages accord with studies investigating the prevalence of gallbladder polyps on post-operative histopathological analysis after cholecystectomy (0.004%–13.8%).2 Histopathologically, gallbladder polyps can be divided into two main categories: neoplastic and non-neoplastic. The great majority of lesions are non-neoplastic, mainly cholesterol polyps, inflammatory polyps and adenomyomatosis. Neoplastic polyps include lesions like adenomas and carcinoma in situ, which harbour malignant potential and can progress into gallbladder cancer, a rare but highly lethal tumour.3 Although there is consensus on the treatment of neoplastic polyps, the differentiation of these polyps pre-operatively remain a diagnostic challenge. Most guidelines advocate cholecystectomy in patients with polypoid lesions measuring 10 mm or more and/or polyp growth. European societies such as European Society of Gastrointestinal and Abdominal Radiology, European Association for Endoscopic Surgery, European Federation - International Society for Digestive Surgery and European Society of Gastrointestinal Endoscopy strongly recommend the 10 mm rule,4 while the most recent guideline on gallbladder polyps by the Society of Radiologists in Ultrasound (SRU) describes a size of 15 mm as associated with risk of malignancy. The SRU reached consensus that growth of up to 3 mm might be part of the natural history of non-malignant polyps, and that 4 mm growth or more per year justifies surgery.5 Both guidelines recognize a paucity of high-quality evidence on this common clinical dilemma. In this issue of United European Gastroenterology Journal, the findings of a single-centre, retrospective cohort study in gallbladder polyp patients are reported.6 The authors aimed to determine whether the growth rate of a gallbladder polyp on ultrasound is an independent risk factor for neoplastic polyps. Therefore, the data from 239 patients with polyps who underwent cholecystectomy after a median follow-up of two years were reviewed. A relevant inclusion criterion for this cohort was the performance of two abdominal ultrasonography examinations at least 6 months apart. Neoplastic polyps were found in 27 patients (11.3%) and non-neoplastic polyps in 212 patients (88.7%). In the analysis, the authors identified three independent predicting factors for neoplastic polyps; the commonly reported polyp size ≥10 mm (with an odds ratio of 3.2), the presence of a solitary polyp (OR 3.5), and a polyp growth rate ≥ 3 mm/year (OR 3.0). The performance of the newly reported prediction model was better compared to a model which only included the 10 mm rule (area under the receiving operator characteristic curve 0.71 vs. 0.65 respectively). The results of this study are of interest and support the recommendations of the current guidelines. But the reported limitations due to selection bias and the retrospective design are not the only reasons to continue research into this topic. As the authors point out, an important limitation of the ‘3 mm growth’ rule is its irrelevance for polyps larger than 6 mm. A large proportion of diagnosed polyps will reach the 10 mm size criterion for cholecystectomy or the 6 mm size criterion in patients with risk factors like age >65. While the use of both risk factors, size >10 mm and age, are debated as solitary independent risk factors for the development of gallbladder cancer in large population-based studies.3, 7 Further improvements in determining gallbladder polyps can come from technological advancements such as high-resolution, contrast-enhanced ultrasound and microvascular imaging.8-12 However, innovation, in this case, comes at the expense of generalisability, as not every centre has access to these advanced ultrasound systems. A more feasible improvement in polyp determination, which the authors also touch on, will come from more dedicated ultrasounds and structured reporting of individual polyp characteristics.11 Lobular surface, sessile polyp, focal wall thickening, vascular core and hypoechogenic internal pattern or foci have been mentioned to increase the chances of a polyp being neoplastic and would provide additional arguments for cholecystectomy. Hyperechoic internal pattern or foci are more common in cholesterol polyps and would prevent cholecystectomy and futile follow-up. However, available studies report only univariate analysis of these morphological features.5, 13-15 Firm conclusions about the risk of malignancy are therefore difficult to draw. In conclusion, gallbladder polyp growth rate should be considered a risk factor for neoplasia. It is advised to perform at least two dedicated ultrasounds within an interval of a maximum of 6 months. Radiologists and sonographers should be motivated to thoroughly scan and report polyp characteristics and, together with surgeons, move forward to a uniform strategy to manage gallbladder polyps and reduce inappropriate follow-up and surgery. Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Topics & Concepts