Pancreatic neuroendocrine tumors: correlation between histogram analysis of apparent diffusion coefficient maps and tumor grade

To explore the role of histogram analysis of apparent diffusion coefficient (ADC) MRI maps based on entire tumor volume data in determining pancreatic neuroendocrine tumor (PNT) grade. Retrospective evaluation of 22 patients with PNTs included low-grade (G1; n = 15), intermediate-grade (G2; n = 4), and high-grade (G3; n = 3) tumors. Regions of interest containing the lesion were drawn on every section of the ADC map containing the tumor and summated to obtain histograms for entire tumor volume. Calculated histographic parameters included mean ADC (mADC), 5th percentile ADC, 10th percentile ADC, 25th percentile ADC, 50th percentile ADC, 75th percentile ADC (ADC75), 90th percentile ADC (ADC90) and 95th percentile ADC (ADC95), skewness and kurtosis. Histogram parameters were correlated with tumor grade by repeated measures analysis of variance with Tukey-Kramer post hoc comparisons. The mADC, ADC75, ADC90, and ADC95 were significantly higher in G1 tumors (1283 +/- A 267; 1404 +/- A 300; 1495 +/- A 318; 1562 +/- A 347 x 10(-6) mm(2)/s) compared to G2 (892 +/- A 390; 952 +/- A 381; 1036 +/- A 384; 1072 +/- A 374 x 10(-6) mm(2)/s) and to G3 tumors (733 +/- A 225; 864 +/- A 284; 1008 +/- A 288; 1152 +/- A 192 x 10(-6) mm(2)/s) (p value < 0.05). Skewness and kurtosis were significantly different between G1 (0.041 +/- A 0.466; 2.802 +/- A 0.679) and G3 (1.01 +/- A 1.140; 5.963 +/- A 4.008) tumors (p value < 0.05). Tumor volume (mL) was significantly higher on G3 (55 +/- A 15.7) compared to G1 (1.9 +/- A 2.7) and G2 (4.5 +/- A 3.6) tumors (p value < 0.05). In this small sample size, we did not detect statistically significant parameters between G2 (n = 4) and G3 (n = 3) tumors. Histographic analysis of ADC maps on the basis of the entire tumor volume can be useful in differentiating histologic grades of PNTs.