Usefulness of Apparent Diffusion Coefficient Values on Diffusion-Weighted Magnetic Resonance Imaging in Small Pancreatic Neuroendocrine Neoplasms.

OBJECTIVES: Whether lymph node dissection is necessary for pancreatic neuroendocrine neoplasms (pan-NEN) smaller than 20 mm in diameter remains controversial. We aimed to investigate the usefulness of apparent diffusion coefficient (ADC) values on diffusion-weighted magnetic resonance imaging (DW-MRI) in predicting lymph node metastasis (LNM) in pan-NENs. METHODS: Data concerning 44 patients with pan-NENs who had undergone radical pancreatectomy in our department between January 2008 and December 2023 were retrospectively reviewed. ADC values of the tumor area on DW-MRI were measured and analyzed in relation to clinicopathological factors. RESULTS: Thirty-three patients had pan-NENs smaller than 20 mm in diameter. Six patients with LNM showed significantly lower ADC values than those without (P=0.0105). Of the patients with pan-NENs smaller than 20 mm in diameter, four patients with LNM had significantly lower ADC values (P=0.0010). Regarding vascular invasion, the patient group positive for lymphatic, venous, and neural invasion had significantly lower ADC values than those in the negative group (P=0.018, 0.036, and 0.033, respectively). CONCLUSION: In cases of pan-NENs smaller than 20 mm in diameter, low ADC values may predict LNM and vascular invasion.