Accuracy of apparent diffusion coefficient in differentiating pancreatic neuroendocrine tumour from intrapancreatic accessory spleen

To evaluate and compare the accuracy of absolute apparent diffusion coefficient (ADC) and normalised ADC (lesion-to-spleen ADC ratio) in differentiating pancreatic neuroendocrine tumour (NET) from intrapancreatic accessory spleen (IPAS). Study included 62 patients with the diagnosis of pancreatic NET (n=51) or IPAS (n=11). Two independent reviewers measured ADC on all lesions and spleen. Receiver operating characteristics (ROC) analysis to differentiate NET from IPAS was performed and compared for absolute and normalised ADC. Inter-reader reliability for the two methods was assessed. Pancreatic NET had significantly higher absolute ADC (1.431x10(-3) vs 0.967x10(-3) mm(2)/s; P < 0.0001) and normalised ADC (1.59 vs 1.09; P < 0.0001) compared to IPAS. An ADC value of >= 1.206x10(-3) mm(2)/s was 70.6% sensitive and 90.9% specific for the diagnosis of NET vs. IPAS. Lesion to spleen ADC ratio of >= 1.25 was 80.4% sensitive, and 81.8% specific while ratio of >= 1.29 was 74.5% sensitive and 100% specific in the differentiation. The area under the curve (AUCs) for two methods were similar (88.2% vs. 88.8%; P=0.899). Both methods demonstrated excellent inter-reader reliability with ICCs for absolute ADC and ADC ratio being 0.957 and 0.927, respectively. Both absolute and normalised ADC allow clinically relevant differentiation of pancreatic NET and IPAS. aEuro cent Imaging overlaps between IPASs and pancreatic-NETs lead to unnecessary procedures including pancreatectomy. aEuro cent Uniquely low ADC of spleen allows differentiating IPASs from pancreatic NETs. aEuro cent Both absolute-ADC and normalised-ADC (lesion-to-spleen ADC-ratio) demonstrate high accuracy in differentiating IPASs from NETs. aEuro cent Both methods demonstrate excellent inter-reader reliability.