Diffusion-weighted MRI: usefulness for differentiating intrapancreatic accessory spleen and small hypervascular neuroendocrine tumor of the pancreas.

Abstract

Background: Image findings of intrapancreatic accessory spleen (IPAS) can closely resemble those of neuroendocrine tumor (NET) of the pancreas. Purpose: To investigate the usefulness of diffusion-weighted imaging (DWI) for differentiating IPAS from small (≤3 cm) hypervascular NET of the pancreas. Material and Methods: The visually assessed signal intensity of pancreatic lesions compared with the spleen on DWI (b value of 1000 s/mm2) and the apparent diffusion coefficient (ADC) values were compared in 25 patients with IPAS and 31 patients with small hypervascular NET. Two blinded radiologists independently rated their confidence in differentiating the two conditions and compared the diagnostic performance of contrast-enhanced magnetic resonance imaging (CEMRI) alone with that of combined CE-MRI and DWI. Results: The isointensity of the pancreatic lesions compared with the spleen on DWI was more frequently observed in IPAS than in NET (92% vs. 12.9%, P<0.001). The mean ADC value was significantly lower in IPAS than in NET (0.90×10-3 mm2/s vs. 1.44×10-3 mm2/s, P<0.001). The sensitivity and specificity of ADC quantification for differentiating the two conditions when using 1.07×10-3 mm2/s as the cut-off value were 96% and 93.5%, respectively. For both readers, the area under the receiver operating characteristic curve and accuracy in differentiating the two conditions of combined CE-MRI and DWI were significantly greater than those of CE-MRI alone (P≤0.039). Conclusion: Visual assessment of DWI and ADC quantification were useful in differentiating IPAS from small hypervascular NET of the pancreas.