[Diagnostic imaging of the CNS disorders]

In this lecture, I attempted to demonstrate MR imaging of the cerebral tracts, medullospinal junction and spinal cord. Cortical migration disorders includes heterotopic gray matter, pachygyria and polymicrogyria. Delayed myelination and dysmyelination are shown as hyper signal intensity in the white matter on T2-weighted images. Edema and demyelination impair the tracts, and they are precisely evaluated by T2-weighted, FLAIR and diffusion-weighted MR images. Reversible posterior leukoencepalopaty syndrome is caused by vasogenic edema of the subcortical association fibers and by cytotoxic edema of the cortical gray matter, due to hypertension, renal dysfunction, drugs and so on. Antiepileptic drug toxicity may cause reversible edema of the splenium. Secondary demyelination includes Wallerian degeneration and transneuronal degeneration. Hypertrophic olivery degeneration is transneuronal degeneration associated with disruption of Guillain-Mollaret's triangle, and it is shown as high signal intensity of the inferior olivery nucleus on T2 and FLAIR images. Limbic system and Papez's circuit play an important role in epilepsy associated with mesial temporal sclerosis. Transneuronal degeneration through the Papez's circuit can be appreciated by the findings of atrophy of the fornix and mammillary body.