Abdominal desmoid in familial adenomatous polyposis presenting as a pancreatic cystic lesion

A 17-year-old male with familial adenomatous polyposis (FAP) presented with chest pain and significant weight loss. An abdominal CT scan detected a cystic pancreatic lesion of unknown etiology. The patient therefore underwent surgical resection of the distal pancreas, which included the lesion, because of the known association of pancreatic cancer with FAP. Histopathological examination of the resected specimen showed a benign pancreatic cyst and fibrous plaque with desmoid fibromatosis adherent to the surface of the pancreas, serosa of the stomach, and colon. The fibrous plaque was histologically identical to the fibrous mesenteric plaque known to occur in FAP and associated mesenteric fibromatosis. We present pathologic evidence that the pancreatic cyst formation was induced by FAP-associated desmoid invasion. Desmoid growth should be considered in the differential diagnosis of a pancreatic cystic mass lesion in patients with FAP or its Gardner syndrome variant. This case report provides the first pathologic evidence for benign epithelial cyst formation in the pancreas caused by fibromatosis invasion of that organ as a part of FAP.