Magnetic resonance imaging in progressive supranuclear palsy and other parkinsonian disorders.
High field intensity MRI may demonstrate signal abnormalities consistent with deposits of iron or other paramagnetic substances in several extrapyramidal disorders. Hallervorden-Spatz disease was the only disorder widely known to have iron deposits in the pallidum, that are now easily demonstrated in vivo by MRI. However, lower field intensity MRI may also demonstrate characteristic findings. In progressive supranuclear palsy, definite atrophy of the midbrain and of the region around the third ventricle is seen in slightly more than half of the cases. Minimal signal abnormalities are sometimes seen in the periaqueductal region, but MRI studies remain of little help in establishing the diagnosis of the disease. Asymmetric atrophy in the parietal regions is seen in corticobasal degeneration, as expected from pathological studies. Minimal alterations may be seen in the substantia nigra in Parkinson's disease. The most interesting MRI findings are observed in multiple system atrophies. Variable abnormal signal intensities, depending on the field intensity, are visible in the putamen in striatonigral degeneration and in Shy-Drager syndrome; in this latter condition the abnormalities are due to its striatonigral degeneration component. Atrophy of the pons, middle cerebellar peduncles, and cerebellum, and signal abnormalities in a characteristic distribution are visible in olivopontocerebellar atrophy. A combination of these posterior fossa abnormalities and putaminal alterations may confirm the involvement of the cerebellar and extrapyramidal systems in multiple system atrophies.