Objectives: To evaluate the value of MR imaging including diffusion-weighted imaging (DWI) for the grading of pancreatic neuroendocrine tumours (pNET).
Material and methods: Between 2006 and 2014, all resected pNETs with preoperative MR imaging including DWI were included. Tumour grading was based on the 2010 WHO classification. MR imaging features included size, T1-w, and T2-w signal intensity, enhancement pattern, apparent (ADC) and true diffusion (D) coefficients.
Results: One hundred and eight pNETs (mean 40 ± 33 mm) were evaluated in 94 patients (48 women, 51 %, mean age 52 ± 12). Fifty-five (51 %), 42 (39 %), and 11 (10 %) tumours were given the following grades (G): G1, G2, and G3. Mean ADC and D values were significantly lower as grade increased (ADC: 2.13 ± 0.70, 1.78 ± 0.72, and 0.86 ± 0.22 10-3 mm2/s, and D: 1.92 ± 0.70, 1.75 ± 0.74, and 0.82 ± 0.19 10-3 mm2/s G1, G2, and G3, all p < 0.001). A higher grade was associated with larger sized tumours (p < 0.001). The AUROC of ADC and D to differentiate G3 and G1-2 were 0.96 ± 0.02 and 0.95 ± 0.02. Optimal cut-off values for the identification of G3 were 1.19 10-3 mm2/s for ADC (sensitivity 100 %, specificity 92 %) and 1.04 10-3 mm2/s for D (sensitivity 82 %, specificity 92 %).
Conclusion: Morphological/functional MRI features of pNETS depend on tumour grade. DWI is useful for the identification of high-grade tumours.
Key points: • Morphological and functional MRI features of pNETs depend on tumour grade. • Their combination has a high predictive value for grade. • All pNETs should be explored by MR imaging including DWI. • DWI is helpful for identification of high-grade and poorly-differentiated tumours.
Keywords: Carcinoma; Grading; Ki-67; Neoplasm; Pancreas.