Pancreatic cancer accompanied by a moderate-sized pseudocyst with extrapancreatic growth

BACKGROUND Pancreatic cancer accompanied by a moderate-sized pseudocyst with extrapancreatic growth is extremely rare. Diagnosis of pancreatic cancer on preoperative imaging is difficult when the pancreatic parenchyma is compressed by a pseudocyst and becomes unclear. Despite advances in imaging techniques, accurate preoperative diagnosis of cystic lesions of the pancreas remains difficult. In this case, it was challenging to diagnose pancreatic cancer preoperatively as we could not accurately assess the pancreatic parenchyma, which had been compressed by a moderate-sized cystic lesion with extrapancreatic growth. CASE PRESENTATION A 63-year-old woman underwent investigations for epigastric abdominal pain. She had no history of pancreatitis. Although we suspected pancreatic ductal carcinoma with a pancreatic cyst, there was no mass lesion or low-density area suggestive of pancreatic cancer. We did not immediately suspect pancreatic cancer, as development of a moderate-sized cyst with extrapancreatic growth is extremely rare and known tumor markers were not elevated. Therefore, we initially suspected that a massive benign cyst (mucinous cyst neoplasm, serous cyst neoplasm, or intraductal papillary mucinous neoplasm) resulted in stenosis of the main pancreatic duct. We were unable to reach a definitive diagnosis prior to the operation. We had planned a pancreaticoduodenectomy to reach a definitive diagnosis. However, we could not remove the tumor because of significant invasion of the surrounding tissue (portal vein, superior mesenteric vein, etc.). The fluid content of the cyst was serous, and aspiration cytology from the pancreatic cyst was Class III (no malignancy), but the surrounding white connective tissue samples were positive for pancreatic adenocarcinoma on pathological examination during surgery. We repeated imaging (CT, MRI, endoscopic ultrasound, etc.) postoperatively, but there were neither mass lesions nor a low-density area suggestive of pancreatic cancer. In retrospect, we think that the slight pancreatic duct dilation was the only finding suggestive of pancreatic cancer. CONCLUSIONS It is difficult to diagnose pancreatic cancer with pseudocyst preoperatively. If a pancreatic cyst is found in patients who had normal tumor marker levels or no history of pancreatitis, we should always consider the possibility of pancreatic cancer. In such cases, slight pancreatic duct dilation may be a diagnostic clue.