Histopathological and neuroimaging studies in partial epilepsy with emphasis on malformations of cortical development

Abstract: The aim of the first part of the present study was to describe the whole Göteborg epilepsy surgery series between 1987 and 1995 with respect to surgical procedures, histopathological findings and clinical correlates. We found a high proportion of malformations of cortical development (MCD) and patients with MCD were studied in further detail in the following studies. Due to the discussion of the significance of microdysgenesis in epilepsy, clinical correlations in this group were specifically studied. Specimens were also analysed to evaluate a new method for assessment of nerve cell distribution in the cortex. To try to find a method to diagnose minor MCD in vivo, a new magnetic resonance imaging technique (diffusion tensorimaging (DTI)) was used. One hundred and thirty-nine consecutive patients were included in the first part of the study. The histopathological specimens were re-evaluated and the morphological findings were correlated to clinical data. A consecutive group of adults (n=33) with temporal lobe resections (between1990-1999) was studied separately and compared histopathologically to 11 post-mortemcontrols. Cortical nerve cell distribution in two specimens with microdysgenesis and two postmortemcontrols were analysed using computer assisted data acquisition. Twenty-two patients with major MCD and 30 healthy volunteers were examined with DTI and the images compared using statistical parametric mapping (SPM).Temporal lobe resection was the most frequently performed procedure (54%) in the whole seriesfollowed by frontal lobe (18%) and multilobar resections (11.5%). Atrophic-gliotic lesions(78%) and MCD (37%) were the most common histopathological findings. Microdysgenesiswas the most common MCD (24%). Microdysgenesis was not found in any of the control specimens.Dual or multiple pathology was commonly seen. Histopathological diagnosis as well as type of resection was of importance for postoperative seizure outcome. The patients with microdysgenesis resembled the patients with major malformations in several clinical aspects: bothgroups had earlier seizure onset and were more often mentally retarded. The new method forevaluation of nerve cell distribution in the cortex suggested higher density of cortical neurons inspecimens with microdysgenesis than in controls. DTI showed abnormalities in 18 patients and in 11 the changes were found in normal appearing tissue beyond the margins of the MCD detectedon conventional magnetic resonance imaging.Multiple pathology was common in epilepsy surgery specimens and further studies are warranted to evaluate the influence of the different histopathological diagnoses on epileptogenesis. MCD was one of the most frequent findings, associated with early seizure onset, mental retardation and a trend for worse outcome after surgery. The clinical resemblance of patients with microdysgenesis to patients with major malformations suggests that this morphological diagnosis is of clinical relevance but further delineation of its histopathology is needed. The here described method for evaluation of cortical nerve cell distribution might prove useful in such delineation. DTI may be useful for preoperative detection of widespread malformative changes that might influence outcome after epilepsy surgery.