Magnetic: Resonance Spectroscopic Evaluation of Brain Tissue Metabolism After Irradiation for Pediatric Brain Tumors in Long-Term Survivors: A Report of Two Cases

Objective The aim of our study was to evaluate the metabolic profile of brain tissue of two long-term survivors of childhood brain tumors. Materials Two males who were 25 and 33 years old at the time of examination and had been irradiated for brain tumors at the age of 17 and 13 years respectively. The first subject had been operated on radically for medulloblastoma and received craniospinal axis irradiation composed of a whole brain radiotherapy with boost to the posterior fossa (total dose (TD) = 59.4 Gy in 33 fractions) and spinal canal irradiation (TD = 30 Gy in 20 fractions) according to the protocol at the time of treatment. The second subject had previously received whole brain irradiation (TD = 45 Gy in 19 fractions) because of inoperable central region tumor of unknown histology. Methods Short echo-tithe (TE=30ms) point-resolved spectra were obtained using a 2 T magnet. Ratios of N-acetylaspartate (NAA), choline (Cho), myo-inositol (mI), lactate (Lac) and lipids (Lip) signal intensities were calculated using the creatine (Cr) signal as an internal reference. The spectra were acquired both from the tumor bed area and uninvolved brain tissue in the first subject, and from uninvolved brain areas of frontal and occipital lobes in the second subject. Results In both cases, MRS examination revealed ratios of NAA/Cr, Cho/Cr and mI/Cr within normal range in most spectra. Nevertheless, a slight elevation of Lac/Cr (2.47 and 1.05) and a more pronounced elevation of Lip/Cr proportions (45.77 and 3.97 respectively, in uninvolved sites) were detected in both Conclusions Metabolic parameters correlated with neuronal function (NAA/Cr) and cell membrane metabolites turnover (Cho/Cr) seem to recover to normal values in long-term survivors of brain tumors. Lac/Cr and Lip/Cr proportions could be considered parameters indicating permanent radiation-induced brain damage; however, this proposal requires further investigation.