Carcinoma in situ of the pancreas detected by progressive focal pancreatic parenchymal atrophy without main pancreatic ductal change.

We report a case in which the progression of focal pancreatic parenchymal atrophy suggested the presence of high-grade pancreatic intraepithelial neoplasia/carcinoma in situ. A 77-year-old man was found to have a pancreatic cyst during a health checkup using transabdominal ultrasound. Contrast-enhanced computed tomography revealed multiple cysts, each measuring ≤ 5 mm, in the pancreatic head and body. Over nine years of intermittent follow-up, imaging showed progressive focal pancreatic parenchymal atrophy extending from the pancreatic head to the body, without changes in the cysts or stenosis or dilatation of the main pancreatic duct. Three-dimensional computed tomography facilitated visualization of the atrophic progression. Transabdominal and endoscopic ultrasound identified a thin pancreatic parenchyma with a surrounding hyperechoic area but no hypoechoic masses. Serial pancreatic juice aspiration cytological examination suggested adenocarcinoma. Surgery was performed, and histopathological examination revealed a 15-mm atrophic region with high-grade pancreatic intraepithelial neoplasia or carcinoma in situ confined to the main pancreatic duct. The lesion extended 5 mm downstream and 10 mm upstream. Even in cases of focal pancreatic parenchymal atrophy without stenosis or dilation of the main pancreatic duct, its progression may indicate high-grade pancreatic intraepithelial neoplasia/carcinoma in situ and warrant serial pancreatic juice aspiration cytology.