Neuroimaging of motor disturbances

High-field MRI has given us a great impact in the clinical diagnosis of various motor disturbances, because the structural abnormalities of the pyramidal tract, basal ganglia and cerebellum are easily observed with this technique. In case of lower motor neuron disease without clinical upper motor neuron sign, proton density-weighted image of the internal capsule and cerebral peduncle is useful for detecting the latent pyramidal tract degeneration. Differential diagnosis of parkinsonism is one of the most successful examples of the clinical use of high-field MRI. Postero-lateral putaminal T2-hypointensity which has been reported to be diagnostic for multiple system atrophy (MSA) might be seen in the aged normal subjects, whereas the proton density weighted image of the normals revealed no abnormal change in signal intensity. In MSA, not only T2-weighted but also proton density image show marked hypointensity in posterior part of putamen. Proton density image of pons, moreover, reveals "four of dice sign" representing the degeneration of the pontine transverse fibers. Another pathological condition which could be differentiated from PD with MRI is PSP. Characteristic "humming-bird sign" of the mid brain on the mid-sagittal section is thought to represent the atrophy of the rostro-dorsal mid-brain tegmentum, where the vertical gaze centers are located. MRI is also useful for differentiating the pathological processes of cerebellar atrophies. Cortical cerebellar atrophy with loss of Purkinje cells shows the disappearance of T2-hypointensity of dentate nucleus, while cerebellipetal atrophy like olivopontocerebellar atrophy causes T2-hyperintensity of cerebellar white matter making dentate hypointensity more conspicuous. Degeneration of the dentate neucleus is revealed by the T2-hyperintensity of dentate contour associated with atrophy of superior cerebellar peduncle at the level of rostral pons.