Background Management of solitary mucinous cystic lesions of the pancreas (MCLs) relies on correct differentiation between branch duct intraductal papillary mucinous neoplasm (BD-IPMN) and mucinous cystic neoplasm (MCN). Current international consensus guidelines recommend resection for MCN, and unifocal BD-IPMN can be followed in the absence of worrisome features/high-risk stigmata. We hypothesized that preoperative differentiation of solitary MCLs is suboptimal, and that all solitary MCLs should be treated similarly. Study Design A retrospective review of an institutional database (2003 to 2016) identified 711 patients who underwent resection for pancreatic cyst. Only lesions that met cytologic or biochemical criteria for diagnosis of MCLs were included. Mucinous cystic neoplasms were defined by presence of ovarian stroma on pathology. Patients with formal preoperative diagnosis of BD-IPMN (multifocality, GNAS mutation) were excluded. Results One hundred and eighty solitary MCLs were identified on preoperative imaging (mean age 54 years, 24% men). On surgical pathology, 108 were MCNs and 72 BD-IPMNs. There was no difference in invasive rate (7 of 108 [6.5%] MCNs vs 4 of 72 [5.6%] BD-IPMN; p ≈ 1). Pancreatic ductal connectivity was reported on imaging/endoscopy in 10 of 108 (9%) MCNs and 22 of 72 (31%) BD-IPMNs, representing 67% accuracy in differentiating MCNs from BD-IPMNs. On multivariate analysis, typical risk factors failed to predict invasiveness in either MCNs or BD-IPMNs. When all undifferentiated solitary MCLs were analyzed together, older age (p = 0.03) and cyst size (p = 0.04) were associated with increased invasive rate in multivariate analysis. Conclusions Unreliable differentiation and limited ability to predict invasiveness make solitary MCLs clinically challenging. With similar invasive rates, MCN and unifocal BD-IPMNs should be merged into one new entity for management, the undifferentiated solitary MCL.
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