Gall Bladder Polyps and Gall Bladder Cancer (Part II)
The prevalence of gallbladder polyps varies from 0.3% to 12% in healthy adults who undergo abdominal ultrasonography.
Gallbladder polyps are classified into 2 groups: neoplastic (adenomas, adenocarcinomas) and non-neoplastic or benign gallbladder lesions include epithelial tumours (adenoma further classified as papillary, tubular or mixed), mesenchymal tumours (fibroma, lipoma, haemangioma) and pseudotumours (cholesterol polyps, inflammatory polyps, adenomyoma).
In a large series, the most common type were cholesterol polyps (62.8%), 7% were inflammatory polyps, 7% had hyperplasia, 5.9% were adenomas, 9.6% were miscellaneous, and only 7.7% were malignant polyps.
It is reported that adenomatous components are present in all the in situ carcinomas and 19 percent of invasive carcinomas may arise directly from these lesions. Two histological types of gallbladder adenocarcinoma may be present resulting from these adenomas, one being derived from ordinary gallbladder epithelium and the other from metaplastic epithelium.
Based on these findings gallbladder carcinomas have been divided into metaplastic and non-metaplastic types according to the presence or absence of metaplastic markers, such as endocrine cells and lysozyme immunoreactivity in the tumor tissue. The metaplastic type is more commonly found in females and the survival rates are better.
The modes of tumor spread also differ, the metaplastic type frequently showing lymphatic spread, whereas the non-metaplastic type usually spread by direct invasion. This classification correlates well with biological behavior and might reflect the histogenesis of gallbladder carcinoma.
Approximately 84% of gallbladder carcinomas are adenocarcinomas, including well, moderately, and poorly differentiated adenocarcinomas, papillary carcinomas, and mucinous or colloid carcinomas. The remaining 16% of gall bladder cancers are adenosquamous, squamous, and even rarer types of carcinomas.
Size is an important determinant of polyps, widely varying incidence rates of 10 to 20 mm (26–88%) and 6 to 10 mm polyps (19–25%) size. Thus, an accurate imaging assessment to differentiate neoplastic gall bladder polyps from non-neoplastic ones is required to overcome the limitations of size criteria alone.
Polyps at risk of malignant transformation are typically rapidly growing and >10 mm in size and solitary/sessile polyps in patients with gallstones of the age of 50+ years.
General consensus guidelines for removal of gallbladder polyps include polyps >10 mm in size, patients older than 60 years, increasing growth on serial imaging until the polyp attains a size of ~10 mm, and/or the presence of gallstones.
A recent study suggests that polyps larger than 2 cm are more likely to harbor high-grade dysplasia/malignancy and the authors concluded that all polyps >2 cm should be removed, whereas those <2 cm can be followed by serial ultrasound every 3–6 months However, up to 40% of malignant gallbladder polyps may be <1 cm in size and thus patients with a polyp of 5–10 mm should be investigated further.