TRANSSYNAPTIC REDUCTION IN N-ACETYL-ASPARTATE IN CEREBELLAR DIASCHISIS - A PROTON MR SPECTROSCOPIC IMAGING STUDY

Objective: To determine if the transneuronal cerebellar hemispheric metabolic asymmetry seen in crossed cerebellar diaschisis, and readily detected with positron emission tomography (PET), is associated with alterations in metabolite signal intensities on [H-1]MR spectroscopic (MRS) imaging when compared with the normal pattern and distribution of cerebellar metabolites. Materials and Methods: The pattern and distribution of metabolites [N-acetyl-aspartate (NAA), choline-containing compounds, creatine, phosphocreatine, and lactate] in the cerebellum, using [H-1]MRS imaging, were studied in a patient with documented long-standing (3 years duration) crossed cerebellar diaschisis and seven normal subjects. Cerebellar diaschisis was detected with fluorodeoxyglucose-PET imaging. Single slice [H-1]MRS imaging was carried out at 1.5 T. Results: There was a marked reduction in NAA signal intensity in the diaschitic cerebellar hemisphere but minimal reduction in choline and creatine signal intensities. The decrease in NAA signal intensity was most marked in the middle cerebellar peduncle and white matter of the diaschitic cerebellar hemisphere. In the normal subjects and in the uninvolved cerebellar hemisphere of the patient the NAA signal intensity was more prominent in the white matter than the cerebellar cortex. Conclusion: Our data indicate (a) transneuronal metabolic effects can be detected with [H-1]MRS imaging and (b) there is a differential distribution of metabolite signal intensities in the cerebellum with NAA signal intensity predominantly localized to axons of the cerebellar fiber tracts rather than neuronal cell bodies in the cortex and the converse is true for choline and creatine signal intensities.