Synaptic plexi of U-fibre layer beneath focal cortical dysplasias: Role in epileptic networks.

ABSTRACT

AIMS: The purpose is to demonstrate heterotopic neurones and their synaptic plexi within the U-fibre layer beneath focal cortical dysplasias (FCD). MATERIALS AND METHODS: This prospective qualitative neuropathological study included 23 patients, ages from 3 months to 17 years resections at epileptogenic foci in 10 FCD Ia; 6 FCD IIa,b; 2 FCD IIIa,d; 3 HME; 2 TSC; 8 controls. TECHNIQUES immunoreactivities for synaptophysin, NeuN, MAP2, SMI32, calretinin, GFAP, vimentin, α-B-crystallin. Bielschowsky silver; LFB; mitochondrial enzyme histochemistry (frozen sections). RESULTS: Subcortical white matter in FCD exhibited neuronal dispersion within U-fibres in FCD I, II and also deep white matter neuronal clusters in FCD II, HME, TSC. Neurones reacted for NeuN, MAP2; few for calretinin. Synaptophysin well demonstrated elaborate U-fibre plexi including axones between U-fibre neurones and projecting to overlying cortex. Deep white matter axones interconnected heterotopia but did not penetrate U-fibres to reach cortex. Mitochondrial enzymatic activity was intense in some neurones, normal in others. Glial α-B-crystallin served as a marker of epileptogenic zones identified electrographically. CONCLUSION: U-fibre synaptic plexi contribute to excitatory circuitry in the cortex and thus to epileptic networks. Deep white matter neurones form local, less integrated plexi except transmantle dysplasias continuous with cortex. U-fibres may be a barrier to axonal penetration from deep heterotopia. Hypermetabolic neurones suggest repetitive ictogenic depolarizations. Gyral resections should include the U-fibre layer. Neuropathology reports should describe subcortical plexi. Synaptophysin immunoreactivity is a valuable supplement for this purpose.
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