A 72-year-old man had been followed up for branch-type mucin producing pancreatic tumor for three years. Endoscopic retrograde cholangiopancreatography (January, 1998) showed a 1.5 cm-sized irregular cystic lesion in the neck of the pancreas, and amorphous filling defects of mucin in the main pancreatic duct. Though the patient had been asymtomatic, endoscopic retrograde cholangiopancreatography (February, 2001) showed the main pancreatic duct obstructed near the origin of the inferior branch. Magnetic resonance cholangiopancreatography showed cluster of cyst near the obstructed main pancreatic duct, and irregular dilatation of upstream main pancreatic duct. Pylorus preserving pancreaticoduodenectomy was performed. Histologically, 1.1-sized invasive carcinoma derived from intraductal papillary carcinoma was detected around the main pancreatic duct near the cyst. In follow-up of the branch-type mucin producing pancreatic tumor, it is necessary to note the possibility of the tumor in the main pancreatic duct near the cyst.
