IMMUNOCYTOCHEMICAL INVESTIGATION ON DYSPLASTIC HUMAN TISSUE FROM EPILEPTIC PATIENTS

In this report we describe three patients with developmental cortical abnormalities (generally referred as cortical dysplasia), revealed by MRI and operated on for intractable epilepsy. Tissue, removed for stri ctly therapeutic reasons, was defined as the epileptogenic area by ele ctroclinical data and stereo EEG (SEEG) recordings. Tissue samples wer e processed initially for histology, and selected sections were furthe r processed for immunocytochemical investigation in order to determine whether the region of cortical dysplasia was co-extensive with the ep ileptogenic area. In two patients with nodular heterotopia, disorganiz ed aggregates of neurons (as revealed by neuronal cytoskeletal markers ) were found within the nodules. Both pyramidal and local circuit neur ons were present in the nodules, but no reactive gliosis was present. When nodules reached the cortex, the cortical layers were disrupted. I n the patient with localized cortical dysplasia, a complete disorganiz ation of the cortical lamination was found, and numerous neurons were also present in the white matter. Disoriented pyramidal neurons weakly labelled with cytoskeletal neuronal markers were also present but no cytomegalic cells were found. One of the patients with nodular heterot opia underwent only partial resection of both the 'epileptogenic area' and of the lesion; this patient still presents with seizures. The oth er patient with nodular heterotopia is seizure-free after a complete l esionectomy and excision of the epileptogenic area. The third patient, with focal cortical dysplasia, had two surgeries; she became seizure- free only after the excision of the epileptogenic area detected by SEE G recording. The present data suggest that the dysplastic areas identi fied by MRI should not be considered as the only place of origin of th e ictal discharges. From the neuropathological point of view, the foca l cortical dysplasia can be considered as a pure form of migrational d isorder. However, the presence of large aggregates of neurons interspe rsed within the white matter, in the subcortical nodular heterotopia, suggests that a defect of neuronal migration could be associated with an exuberant production of neuroblasts and/or a disruption of mechanis ms for naturally occurring cell death. (C) 1998 Elsevier Science B.V, All rights reserved.