Intraductal papillary mucinous tumor (IPMT)

SURGICAL AND PATHOLOGIC FINDINGS

In our patient, the hypodense solid mass is typical of duct-cell adenocarcinoma, while the small adjacent cysts are typical for branch-duct IPMT. The main pancreatic ductal marked dilatation and parenchymal atrophy suggest that main-duct IPMT was present as well. An intraoperative evaluation showed a palpable solid pancreatic head mass with no other palpable pancreatic abnormalities. During incision of the pancreatic mass, cloudy whitish fluid was observed that was thought to be from the pancreatic duct. Histopathologic evaluation of the surgical wedge biopsies found mucinous cells arising from the pancreatic duct epithelium (Figure 2A). The solid pancreatic mass was found to represent poorly differentiated invasive adenocarcinoma (Figure 2B).

Findings

Contrast-enhanced computed tomography (CT) performed with 5-mm thick slices obtained at 5-mm intervals revealed a 3.5-cm solid, slightly hypodense, pancreatic head mass with obstructive dilatation of the intrahepatic biliary, common bile, and pancreatic ducts (Figure 1). The pancreatic duct measured 2.0 cm in diameter. The pancreatic parenchyma was marked-ly atrophic. Small cysts were present in the pancreatic head adjacent to the solid mass. No regional lymphadenopathy or solid hepatic lesions were seen.

Discussion

Intraductal papillary mucinous tumor, which was first described in 1982, is either a new pancreatic entity or a previously miscategorized tumor. In 1996, the World Health Organization separated mucinous ductal ectasia of the pancreas from mucinous cystadenomas and officially assigned the name intraductal papillary mucinous tumor of the pancreas. Approximately 1% of all pancreatic malignancies and 10% to 13% of pancreatic cysts are IPMTs.^1,2 A premalignant or malignant neoplasm of pancreatic ductal epithelium, IPMT often masquerades as idiopathic chronic pancreatitis. In contrast to other pancreatic cystic lesions, IPMTs are intraductal and have a marked mucin hypersecretion, which results in characteristic imaging and endoscopic appearances. The diagnosis is made using a combination of CT, magnetic resonance imaging, endoscopic retrograde cholangiopancreatography, endoscopic ultrasound, and biopsy. Although it is well known that IPMTs can be malignant at presentation or can undergo malignant transformation, to our knowledge, an imaging diagnosis of coexisting benign-appearing IPMT and carcinoma has not been reported.

IPMT is characterized by intraductal cuboid or tall columnar epithelium proliferation and abundant mucin production that causes ductal dilatation. Cells are arranged in a papillary or cribriform configuration in ectatic or cystically dilated pancreatic ducts. The World Health Organization classification divides IPMT intraductal epithelial dysplasia into adenoma, borderline tumor, and carcinoma.³ This histologic continuum from hyperplasia and dysplasia to invasive carcinoma can be found within a single pancreas representing evolution to malignancy versus multicentricity of dysplastic epithelium.⁴ Roughly 30% to 40% of patients with IPMTs have invasive malignancy at the time of diagnosis, and the remaining patients have atypia, dysplasia, or carcinoma in situ, all of which illustrate IPMT's premalignant nature.⁵

Currently, IPMTs are categorized into main-duct (diffuse or segmental) and branch-duct (microcystic or macrocystic) types. Main-duct IPMT is usually multifocal and represents a global ductal epithelial disorder. A macrocystic branch-duct tumor is characterized by unilocular or multilocular architecture. A microcystic branch-duct tumor is manifested by multiple thin septa that separate small cystic spaces.

Diagnosis is not usually made until 5 to 6 years after the onset of symptoms, which include weight loss, jaundice, anorexia, steatorrhea, and diabetes mellitus. Invasive malignancy is diagnosed in 30% to 45% of patients at the initial staging. An elevated CA19-9 level has been correlated with invasive disease.⁶ A recent study found a correlation between the average size of a soft tissue mass associated with IPMT and pathology: 2.0 cm for hyperplasia; 3.0 cm for adenoma; and 4.8 cm for adenocarcinoma.⁴ Additional studies that evaluated IPMTs with axial imaging found septations in 49%, filling defects in 31%, nodular soft tissue regions in 5%, multiplicity of lesions in 23%, and bulging papilla in 25%.^7,8

Total pancreatectomy is the suggested treatment in most cases, since IPMT is considered to be a premalignant state that involves the entire pancreatic ductal epithelium. Subtotal pancreatic resections are performed according to the patient's underlying morbidity and compliance and for palliative intervention.⁵

In many patients (particularly those with the branch-duct type), the tumor is an incidental finding. Serial evaluation of small cystic lesions has documented a predilection for the malignant progression of main-duct lesions and the stability of branch-duct lesions. Isolated branch tumors that are <2.5 cm and do not have a solid component can be observed, since these are usually adenomas.⁸ For IPMTs that originate in a branch duct, resection is recommended if the main duct is dilated.

CONCLUSION

We conclude that when a mass that is consistent with duct-cell carcinoma is seen adjacent to a cystic mass that is consistent with IPMT, the diagnosis of adenocarcinoma coexisting with IPMT can be suggested. This could be the result either of malignant degeneration of IPMT or a manifestation of de novo malignant IPMT.

1. Kawarada Y, Yano T, Yamamoto T, et al. Intraductal mucin-producing tumors of the pancreas. Am J Gastroenterol. 1992;87:634-638.
2. Warshaw AL, Compton CC, Lewandrowski K, et al. Cystic tumors of the pancreas. New clinical, radiologic, and pathologic observations in 67 patients. Ann Surg. 1990;212:432-445; discussion 444-445.
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