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 < 0.0001). The overall diagnostic accuracy, positive predictive value (PPV) and negative predictive value (NPV) of the qualitative assessment for the use of DWI in differentiating tumors recurrence from post-treatment changes were 96.6%, 96% and 83.3%, respectively. Upon quantitative analysis of the DW imaging data, a threshold ADC value of 1.3 × 10⁻³ mm²/s used for differentiating between post-treatment changes and recurrent cancers showed the highest combined sensitivity of 94%, specificity of 83.3%, accuracy of 93.6%, positive predictive value of 95.9%, and negative predictive value of 83.3%.

DW MRI is a promising non-invasive MRI technique used to differentiate recurrent/residual head and neck malignancies from posttreatment changes based on ADC values. DWI offers advantage as it has a short scanning time and can be safely added to standard MRI protocol with minimum patient discomfort. Complementary use of DWI and PET/CT imaging may increase diagnostic confidence for differentiating recurrent disease from radiation therapy-induced changes after 6–12 months in posttreatment cases.