- A clinical diagnosis of IPMN with main duct involvement will be determined by the surgeon caring for the patient. Main duct involvement may be suspected where there is a significant radiographic character change (cystic dilation) in the main pancreatic duct (independent of ductal diameter), a significant "step-up" in main duct diameter (2-3 fold) or a significant segmental or diffuse dilation of the main pancreatic duct (> or equal to 4mm) as defined by CT, MRCP, EUS or ERCP.