[Magnetic resonance spectroscopy of brain tumours]

Magnetic resonance spectroscopy facilitates non-invasive determination of metabolic changes in vivo. The main metabolites are the neuronal marker N-acetylaspartate (NAA), cholines reflecting membrane turnover, creatine, lactate, and mobile lipids. Primary brain tumours exhibit reduced NAA and increased choline resonances compared to normal brain, and these abnormalities increase with higher malignancy. Increasing choline resonances on follow-up studies correlate with tumour progression, whereas the reduction of initially increased choline resonances indicates a transition from viable tumour to necrotic tissue. Metastases as non-neuroectodermal tumours lack NAA, but demonstrate elevated choline, lactate and lipid resonances. Lymphomas are characterised by massively increased lipid resonances with markedly elevated choline. Prominent alanine resonances are often observed in meningioma. Cystic/necrotic lesions demonstrate elevated lactate regardless of their aetiology. The characteristic finding of prominent resonances from acetate, succinate, and alanine, of leucine, isoleucine and valine in untreated bacterial abscesses allows the differentiation of bacterial abscesses from cystic/necrotic brain tumours.