Mucin-secreting tumors of the pancreas.
Mucinous pancreatic neoplasms present diagnostic and therapeutic challenges. These tumors behave in an indolent nature, with frequent overlap of symptoms and radiographic appearance with other forms of pancreatic cysts, pseudocysts, and malignancy. Some authors propose that all mucin-producing tumors of the pancreas are variants of the same basic entity and have subclassified them on the basis of their predominant location within the pancreas. These disorders must be considered in the evaluation of chronic abdominal pain, particularly in the presence of a cystic pancreatic lesion or when associated with idiopathic chronic or acute recurrent pancreatitis. The clinicopathologic features of IMHN overlap to a great extent with classic mucinous cystic neoplasms but are different significantly enough to be distinct clinical entities. These tumors originate from the pancreatic duct epithelium, produce mucin, demonstrate a papillary growth pattern, and are considered premalignant or frankly malignant at the time of diagnosis. Both lesions biologically are much less aggressive than that of pancreatic ductal adenocarcinoma and appear to infiltrate peripancreatic tissue and to metastasize to lymph nodes or other adjacent structures late in the course of disease. Nevertheless, IMHNs are located primarily in the head of the pancreas, commonly affect elderly men, and present clinically with obstructive pancreatitis, often leading to pancreatic insufficiency, whereas mucinous cystic neoplasms are more likely to develop in the pancreatic body or tail, predominate in young women, and present with symptoms referable to tumor compression of adjacent structures. The location of the lesion is the primary differentiating feature because the lining epithelium of the two tumor types is indistinguishable pathologically. In mucinous cystic tumors, the mucus is secreted and retained within the cyst lumen because of the absence of communication between the cyst and the main pancreatic duct. In contrast, mucus produced in MDE flows into the main pancreatic duct, resulting in obstructive pancreatitis and, ultimately, dilatation of the pancreatic duct. Intraductal mucus provides an important clue to the diagnosis of intraductal pancreatic neoplasms and, whenever present, should prompt an aggressive diagnostic evaluation. Both lesions are managed by resectional surgery because the opportunity for cure is high in the absence of metastatic disease.