Role of DWI/ADC in evaluation of brain tumor and monitoring treatment response

Abstract

DWI consists of a DW image-diffusion trace and ADC map. DW image is a T2-weighted echo planar background image attenuated by the rate of apparent diffusion and with qualitative and quantitative assessment of the ADC map provide distinction of cytotoxic and vasogenic edema. DWI/ADC is used to assess brain tumors, tumor grading by providing information about tumor cellularity- prediction of tu grade. In high grade tumors DWI/ADC evaluate diffuse unenchancing spread and terapeutic response. ADC value of high grade gliomas has been shown to be lower than that of low-grade gliomas. In extra axial meningioma low ADC in atypical vs typical subtypes. Primary neoplasms- peritumoral edema/infiltration = low ADC vs secondary lesions. Lymphoma - high DWI/ low ADC due to its cellularity. DWI/ADC of therapeutic response provide information about post oper margin of surgical resection (ischemia, pyogenic infection-reduction of ADC). Useful in following treatment response and recurrence because cytotoxic chemoradiation reduce cellularity - increase ADC. Radiation necrosis usually showed heterogeneity on DWI images and often included spotty, marked hypointensity (Chiaki Asaoa, et al.AJNR2005). DWI useful in differentiating recurrent neoplasm from radiation necrosis. Material and method: We evaluate 33 cases with brain tumor. 19 of them after operative and/or chemoradiation therapy. All of them underwent on brain MRI enhanced with DWI/ADC, B-value o and 1000s/mm2 on 1,5T SIMENS Avanto. Results: From intraaxial tumor: 4 cases of glioma gr1; 5 gr2; 3 gr3 and 9 gr4; extraaxial 7 from witch 2 atypical and 5 secondary lesions. Follow up on operated gr2 and follow up on oper. and chemoradiated gr3 and 4 with detection of postradiation necrosis, residual tumor and recidiv however transformation in higher grade. Conclusion: Information about tumor type, malignancy grade, and the presence of necrosis is useful to determine the most suitable and effective treatment procedures. Serially obtained diffusion data is useful to document and even predict cellular response to drug or radiation therapy. Today DWI/ADC is necessary tool in CNS examination. DWI practical, useful, requires less imaging time vs other advance techniques but alone insufficient.