There have been few reports on (1) the nature and pathogenesis of small cystic lesions of the pancreas, (2) their incidence, age distribution, and location, and (3) their significance as potential precursors of intraductal papillary tumors, mucinous cystic tumors, and duct cell carcinomas.
Materials: Epithelial growth of small cystic lesions in 300 consecutive autopsy cases and in seven cases of small duct cell carcinoma from among 2300 elderly autopsy cases, was evaluated by histopathological analysis. One hundred eighty-six cystic lesions were found in 73 of 300 autopsy cases (24.3%). The incidence of cystic lesions increased with age. Cystic lesions were equally distributed throughout the pancreas. Epithelial atypia was histologically classified into five groups: normal epithelium; papillary hyperplasia without atypia; atypical hyperplasia; carcinoma in situ; and invasive carcinoma. The incidence of each group was 47.5, 32.8, 16.4, 3.4, and 0%, respectively. Epithelia of atypical hyperplasia or carcinoma in situ were more prevalent in small cystic lesions (less than 4 mm in diameter) than in larger lesions (chi-square test, p < 0.05). Epithelia of dilated ductular branches adjacent to cystic lesions showed a similar degree of atypia as the epithelia of the cystic lesions themselves (p < 0.01). Epithelial atypia of the main pancreatic duct was mild in all of the cases but two, and was not related to that of the cystic lesion. Among the seven cases of small duct cell carcinoma, two cases had small cancerous cystic lesions, 4.1 and 5.3 mm in diameter, within the tumor. Small cystic lesions appear to have the potential to progress to malignancy but definitive evidence has not been demonstrated. Additional studies, including molecular biological examinations, are necessary to fully understand the biology of these lesions.