Differentiation Between Recurrent Brain Tumor And Radiation Injury Using Magnetic Resonance Spectroscopy In Combination With Diffusion Weighted Imaging

When a patient with a previously irradiated brain tumor develops a new contrast-enhancing lesion on routine follow up MRI, the clinical question is referred as “recurrent tumor versus radiation injury”.MR spectroscopy and DW imaging allow for the assessment of metabolism and physiology and thus improving the possibilities of better characterization of treatment-related changes.The aim of this study was to detect the diagnostic role of MR spectroscopy combined with diffusion-weighted imaging in the evaluation of the recurrent contrast-enhancing lesions at the site of the previously irradiated brain tumors.This study included 40 patients (27 males and 13 females, their ages ranged between 3 years to 65 years) fulfilled all the inclusion criteria.MR spectroscopy and DW imaging were performed in all patients. Spectral data for NAA, Cho, Cr, Lip/Lac were evaluated and Cho/Cr, Cho/NAA and NAA/Cr ratios were calculated in combination with the ADC value and ADC ratio in all patients.On the basis of MR spectroscopy findings, the study population (40 patients) were classified into two groups, tumor recurrence (25 patients {62.5 %}) and radiation necrosis (15 patients {37.5 %}).In our study we found:MR Spectroscopy findings:The mean metabolite ratios (± SD) for Cho/Cr, Cho/NAA and NAA/Cr in the tumor recurrence group were 3.05±1.68, 3.3±2.5 and 1.27±1.1 respectively and in the radiation necrosis group were 0.59±0.5, 0.71±0.68 and 0.8±0.59 respectively.There were statistically highly significant differences between patients with tumor recurrence and patients with radiation necrosis regarding calculated metabolite ratios for Cho/Cr and Cho/NAA but not for NAA/Cr. The Cho/Cr and Cho/NAA ratios were significantly higher in tumor recurrence group than in radiation necrosis group (p < 0.001 for both ratios)Diffusion Weighted imaging findings:The mean ADC value (± SD) and mean ADC ratio (± SD) for the tumor recurrence group were 1.07±0.43 × 103 mm2/s and 1.18±0.47 respectively and for the radiation necrosis group were 1.59±0.42 × 103 mm2/s and 1.72±0.46 respectively.There were statistically highly significant differences between patients with tumor recurrence and patients with radiation necrosis regarding ADC value and ADC ratio.The ADC value and ADC ratios were significantly lower in tumor recurrence group than in radiation necrosis group (p < 0.001 for both).