Age-related metabolic changes in the upper brainstem tegmentum by MR spectroscopy

Several neurodegenerative disorders have a profound metabolic and structural impact on the brainstem. MR spectroscopy provides metabolic information non-invasively and has the potential to characterize the changes associated with normal aging and differentiate them from neurodegenerative alterations. The present work was aimed at studying the upper brainstem tegmentum at the midbrain and pontine levels in 57 adult normal volunteers, aged 23-79 years, with long-echo time proton MR spectroscopy to evaluate possible regional differences and the effect of age. Higher ratios of N-acetyl aspartate (NAA)/total creatine (Cr) and choline-containing compounds (Cho)/Cr were observed in the pons compared to the midbrain, resulting from higher net NAA and Cho content. In the midbrain, there was a linear decline of NAA and Cho with age in subjects over 50, most probably related to neuronal tissue loss. In the pons, such an aging effect was not observed, with subjects over 50 showing higher Cr and Cho than the under-50 subjects. Our findings provided evidence of regional differences and suggest different effects of age on the two studied brainstem segments, hitherto undescribed.