Imaging considerations in intraductal papillary mucinous neoplasms of the pancreas

Abstract

With the widespread use of cross-sectional imaging, particularly computed tomography (CT) and magnetic resonance imaging (MRI), and the continuous improvement in the image quality of these techniques, the diagnosis of incidental pancreatic cysts has increased dramatically in the last decades. While the vast majority of these cysts are not clinically relevant, a small percentage of them will evolve into an invasive malignant tumor making their management challenging. Mucinous cystic neoplasms and intraductal papillary mucinous neoplasms (IPMN) are the most common pancreatic cystic lesions with malignant potential. Imaging findings on CT and MRI correlate tightly with the presence of malignant degeneration in these neoplasms. IPMN can be classified based on their distribution as main duct, branch duct or mixed type lesions. MRI is superior to CT in demonstrating the communication of a branch duct IPMN with the main pancreatic duct (MPD). Most branch duct lesions are benign whereas tumors involving the MPD are frequently associated with malignancy. The presence of solid nodules, thick enhancing walls and/or septae, a wide (> 1 cm) connection of a side-branch lesion with the MPD and the size of the tumor > 3 cm are indicative of malignancy in a branch and mixed type IPMN. A main pancreatic duct > 6 mm, a mural nodule > 3 mm and an abnormal attenuating area in the adjacent pancreatic parenchyma on CT correlates with malignant disease in main duct and mixed type IPMN. An accurate characterization of these neoplasms by imaging is thus crucial for selecting the best management options. In this article, we review the imaging findings of IPMN including imaging predictors of malignancy and surgical resectability. We also discuss follow-up strategies for patients with surgically resected IPMN and patients with incidental pancreatic cysts.

Keywords: Computed tomography; Intraductal papillary mucinous neoplasms; Magnetic resonance imaging; Pancreatic neoplasms.

Figure 1

Coronal maximum intensity projection from a 3D T2-weighted MRCP acquisition shows a cystic lesion in the uncinate process of the pancreas (asterisk) and a communicating branch duct (arrow) between the cyst and the normal caliber main pancreatic duct. These findings are characteristic of a branch duct intraductal papillary mucinous neoplasm and this lesion has been stable on follow up MRCP examinations for 3 years.

Figure 2

Axial T2-weighted (A) and subtraction (post-contrast minus pre-contrast) (B) images at the level of the pancreas demonstrate marked enlargement of the main pancreatic duct (arrowheads) with intraluminal enhancing papillary projections (arrows). Main duct intraductal papillary mucinous neoplasm with in situ carcinoma was confirmed at histopathology after total pancreatectomy. Multiple renal cysts (asterisks).

Figure 3

Axial contrast enhanced computed tomography image at the level of the head of the pancreas shows a cystic lesion (asterisk) in the uncinate process of the pancreas with a hypoattenuating area (arrow) in the adjacent pancreatic parenchyma. Note the intrahepatic biliary dilatation (arrowheads) due to obstruction of the common bile duct (not shown) by the infiltrating mass. Invasive pancreatic adenocarcinoma arising from an intraductal papillary mucinous neoplasm was confirmed at pathology after a Whipple procedure. GB: Gallbladder.