[MRI study of degenerative process in multiple system atrophy]

The characteristic morphological changes of the brainstem and cerebellar regions of multiple system atrophy (MSA) were studied by MRI in varying subtypes, that is olivoponto cerebellar atrophy (OPCA: 23 cases), striatonigral degeneration (SND: 7 cases) and Shy-Drager's syndrome (SDS: 9 cases). OPCA was characterized by atrophy of the entire regions of the brainstem and the cerebellum. SND and SDS tended to show atrophy similar in type but lessin extent to OPCA. The common lesions in MSA were atrophy of the pontine base and cerebellum, and dilation of the fourth ventricle. Atrophy of the pontine base was more dominant in the inferior part than in the superior part, and cerebellar atrophy was more dominant in the superior part than in the inferior part, indicating that degeneration of the pontocerebellar pathway proceeds principally along fibers connecting the inferior part of the pons and the superior part of the cerebellum. Dilation of the fourth ventricle indicated atrophy of the middle cerebellar peduncle. In almost all the cases of OPCA and about a half the cases of SND and SDS, the pontine base and the middle cerebellar peduncle appeared as high signal intensity on T2 weighted image and as low intensity on T1, suggesting degeneration and demylination. In a few cases of OPCA, the dorsolateral part of the putamen were demonstrated as low signal intensity on T2 weighted image.