B. IPMN: diagnostic and staging criteria

Intraductal papillary mucinous neoplasms (IPMNs) of the pancreas originate from the mucinous epithelium of the pancreatic duct system and are characterised by papillary growth, hyper-production of mucin causing ductal dilatation. The gross appearance of these tumours depends on the site of origin, along the pancreatic duct system: we can distinguish IPMNs of the main pancreatic duct (MPD) (both with segmental or diffuse involvement), IPMNs of the side branches (SB) or IPMNs of both MPD and SB (mixed type). Histologically, IPMNs are classified into adenomas, border-line tumours and carcinomas, depending on the basis of the degree of cytoarchitectural atypia. Malignancy can occur in 30-88% of IPMNs, as an in situ or invasive cancer. A stepwise progression from adenoma to carcinoma has been hypothesised, because of the coexistence of different degrees of dysplasia in the same tumour. The risk of malignant degeneration correlates with the site of origin of the tumour. IPMNs typically produce radiographically identifiable ductal dilatation secondary to production of large amounts of mucin, which may predominantly involve the main pancreatic duct, branch ducts or both. Different imaging modalities including computed tomography (CT), magnetic resonance (MR) imaging or MR cholangiopancreatography, endoscopic retrograde cholangiopancreatography (ERCP), transabdominal ultrasonography (US) and endoscopic US have been used to evaluate IPMNs, and each modality has advantages and disadvantages that will be illustrated