Diffusion-weighted echo-planar MRI: A valuable tool for differentiating primary parotid gland tumors?

Purpose: To investigate the feasibility of using diffusion-weighted (DW) echo-planar imaging (EPI) for differentiating primary parotid gland tumors. Material and Methods: Fifty consecutive patients with a suspected primary tumor of the parotid gland were examined with a DW EPI sequence TR 1,500 msec, TE 77 msec, field of view 250 x 250mm, pixel size 2.10x1.95mm, section thickness 5mm). The b factors used were 0, 500, and 1,000 sec/mm(2). Apparent diffusion coefficient (ADC) maps were digitally transferred to MRIcro (Chris Rorden, University of Nottingham, Great Britain) and evaluated with a manually placed irregular region of interest (ROI) containing the entire tumor. Additionally, the contralateral, non affected parotid gland was measured and a circular ROI containing 100200 pixels was placed in the cerebrospinal fluid (CSF) next to the spinal cord in every patient. For comparison of the results, the two-tailed Student's t test was used, based on the median ADC values for each patient, and a p-value <.05 was determined to indicate statistical significance. Results: In 45 patients, a primary neoplasm of the parotid gland could be histologically verified. For the non-affected parotid glands of all 45 evaluated patients, the mean ADC value was 1.14 x 10(-3) mm(2)/sec 0.12 x 10(-3) mm(2)/ sec (mean standard deviation). Seven different entities of parotid gland tumors were histologically discriminated. Pleomorphic adenomas (2.14 x 10(-3) mm(2)/sec 0.11 x 10(-)3 mm(2)/sec), Warthin tumors (0.85 X 10(-3) mm(2)/sec 0.1 x 10(-)3 mm(2)/sec), and mucoepidermoid carcinomas (1.04 x 10(-3)mm(2) /sec 0.3 x 10(-3) mm(2)/sec) showed statistically significant different ADC values in comparison to all other evaluated tumors (p.001), and also among each other (p <.001). Additionally, ADC values presented by lipomas were statistically significant compared to all other entities (p <.001 to .015). Among primary malignant parotid gland tumors, no statistically significant ADC values could be observed (p.18 to 1). Conclusion: Diffusion-weighted echo-planar MRI seems to be a valuable tool for differentiating benign from malignant primary parotid gland tumors.