Value of diffusion MR imaging in differentiation of recurrent head and neck malignancies from post treatment changes

•Recurrent lesions have significantly lower ADC value than that of post treatment changes.•ADC has 96% sensitivity, 83.3% specificity, 96% positive predictive value, 83.3% negative predictive value and 96.6% accuracy in differentiating residual/recurrent disease from post treatment changes.•Positive & negative predictive value, sensitivity, specificity of differentiating tumor recurrence from post treatment changes with PET-CT was 90.6%, 100%, 100% and 40%. Role of diffusion-weighted (DW) MR imaging in differentiating residual or recurrent neck malignancies from postoperative/post-radiation changes with histopathological correlation and comparison with PET-CT. Prospective observational study for a period of 1 year in 62 post-radiation/post-operative patients suspected to have residual/recurrent tumors of neck with lesion diameter more than 5 mm measured on MRI. Mean ADC for recurrent/residual tumors: 1.008 ± 0.220 × 10−3 mm2/s - significantly lower than mean ADC value for post-treatment changes of 1.69 ± 0.40 × 10−3 mm2/s (p