Main pancreatic duct obstruction due to a small nonfunctioning endocrine tumor of the pancreas

A 65-year-old Japanese male was referred to our hospital for evaluation of a main pancreatic duct obstruction. Two months previously, he had suffered an attack of acute pancreatitis that was resolved with conservative treatment. Dynamic contrast-enhanced study by multidetector row computed tomography revealed a well-enhanced 5 x 5 mm mass in the head of the pancreas with dilatation of the main pancreatic duct in the body and tail. On endoscopic retrograde pancreatography, obstruction of the main pancreatic duct in the head of the pancreas was noted. Pancreatic juice cytology was nondiagnostic. Endoscopic ultrasonography demonstrated a well-defined hypoechoic mass, about 5 mm in size, with distal main pancreatic duct dilatation. The patient underwent elective pylorus-preserving pancreaticoduodenectomy. Pathological examination revealed a well-differentiated endocrine tumor of the pancreas of uncertain behavior, 5 mm in size. Immunohistochemically, the tumor was diffusely positive for chromogranin A and synaptophysin, and focally it was positive for insulin, glucagon, and CA19-9; it was negative for gastrin. The final diagnosis was main pancreatic duct obstruction secondary to a nonfunctioning endocrine tumor of the pancreas of uncertain behavior. Of note, a small nonfunctioning endocrine tumor of the pancreas is important in the differential diagnosis of main pancreatic duct obstruction demonstrated by radiographic examinations.