Mesial Temporal (Hippocampal) Sclerosis

      Hippocampal sclerosis is characterized by neuronal loss and gliosis with secondary atrophy and sclerosis. With additional involvement of the amygdala and parahippocampal gyrus, the term mesial temporal sclerosis (MTS) is appropriate. The etiology is not certain, however, febrile seizures during infancy have been implicated in a number of series. The neuronal loss and gliosis occurs in all segments of the cornu ammonis and dentate gyrus, but it is most prominent in the CA1 region with relative sparing of the CA2 segment. The involvement is usually most prominent in the body of the hippocampus, followed by the tail and head. Bilateral disease is seen in 10-15% of cases. With unilateral hippocampal sclerosis, anterior temporal lobe resection cures the epilepsy in 90% of

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patients. Endnote

      The most common findings on MR imaging are hippocampal atrophy and hyperintensity on T2- weighted images. FLAIR images are most sensitive for detecting the abnormal hyperintensity, however, high signals from the choroid plexus or CSF flow artifacts in the temporal horn can be confusing. Endnote

With high resolution imaging, loss of the normal internal architecture of the hippocampus can be identified. Endnote MR imaging is reported to be 80-90% sensitive for detecting hippocampal sclerosis. Quan titative volume measurements from thin-section 3D MR sequences can increase the sensitivity. Endnote   Associ ated findings include atrophy of the parahippocampal gyrus, decreased volume of the adjacent white matter, and temporal horn dilatation. Since the fornix is the primary efferent pathway from the hippocampus, severe damage to the hippocampal neurons can result in atrophy of the ipsilateral fornix. Endnote Gadolinium enhancement is not helpful for the diagnosis of hippocampal sclerosis. 

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