Comparison of Surgically Resected Polypoid Lesions of the Gallbladder to their Pre-operative Ultrasound Characteristics

Abstract

Background

Polypoid lesions of the gallbladder (PLG) have been a common finding on ultrasound examinations of the abdomen and are more prevalent since our use of equipment incorporating pulse shaping increased bandwidth, and enhanced phase use for image reconstruction began in 1996. Our study correlates the pre-operative ultrasonographic findings of these lesions to the surgically resected specimen with specific regard to identifying neoplastic polyps.

Methods

A retrospective review was performed of 130 patients who had a pre-operative ultrasound of the gallbladder and subsequently underwent cholecystectomy between August 1996 and July 2007 at the Mayo Clinic Rochester.

Results

Seventy-nine pseudopolyps (cholesterol polyps, inflammatory polyps, and adenomyomas) and 15 neoplastic polyps were identified on histopathologic analysis. However, 36 patients (27%) did not have a PLG upon histopathologic analysis. Thirty-one polyps had suspicious ultrasonographic characteristics for neoplastic changes. Twenty-nine were ≥10 mm, 12 had vascularity, and one demonstrated invasion. Of these, there were 23 pseudopolyps and six true polyps with neoplastic changes on final pathology (four dysplastic adenomas and two adenocarcinomas). Three asymptomatic polyps ≤10 mm (4%) in maximum diameter based on pre-operative ultrasound imaging (US) had neoplastic changes at pathology (two dysplastic adenomas and one adenocarcinoma). Several statistically significant risk factors were identified that increased the likelihood for malignancy in a PLG: history of primary sclerosing cholangitis (PSC), local invasion, vascularity, and ≥6 mm maximum diameter based on pre-operative US. Of PLGs ≤10 mm, 7.4% were neoplastic. Twenty-five patients were followed up with at least two serial ultrasound examinations. Of these, seven demonstrated polyp growth. None of these specimens demonstrated neoplastic changes. The positive predictive value (PPV) and negative predictive value (NPV) for ultrasound diagnosing neoplastic changes based on current criteria was 28.5% and 93.1%, respectively, with a false negative rate of 5.0%. Expanding the criteria to include cholecystectomy for PLGs ≥ 6 mm changes the positive predictive value and negative predictive value to 18.5% and 100%, respectively, with a false negative rate of 0%.

Conclusion

Histopathologic analysis of polypoid lesions of the gallbladder continues to be the gold standard to identify malignancy. Ultrasound has been used extensively in the pre-operative management of these lesions, but modern ultrasound techniques are unable to differentiate between benign and malignant PLGs with any certainty. We recommend that strong consideration be given to surgical resection of PLGs ≥ 6 mm based on pre-operative US due to the significant risk of neoplasm. Additionally, PLGs in all patients with PSC, any patient in whom diligent long-term follow-up cannot be completed, and lesions that demonstrate growth, vascularity, invasion, or are symptomatic require cholecystectomy.