Abstracts

Rationale: GCD (granule cell dispersion) is a common phenomenon occurring in almost 50% of mesial temporal sclerosis (MTS) specimens. Little is known about its pathogenic mechanisms and clinical significance. Hippocampus plays a crucial role in learning and memory. Seizure frequency, duration of epilepsy, antiepileptic drugs, and interictal epileptiform discharges, have been implicated in the memory dysfunction in mesial temporal lobe epilepsy (MTLE) patients. Histopathological investigation of surgical specimens may also help understand memory impairment in these patients. Human studies and animal models have correlated the degree of hippocampal and dentate gyrus (DG) cell loss with memory decline. We studied the occurrence of GCD in refractory MTLE-MTS patients and investigated the relationship between this abnormality and memory performance, clinical characteristics, patterns of MTS, as well as surgical outcome. Methods: Fifty-four patients (27 men), all right-handed, with medically refractory MTLE and unilateral MTS (27 right and 27 left) on MRI were included in this study. Right and left MTLE patients were separated in GCD and no-GCD groups. All patients had extensive presurgical evaluation including high-resolution MRI and prolonged noninvasive video-EEG recording, and when concordant data was obtained in this evaluation, a surgical resection was performed. Logical Memory I and II and the Rey Auditory Verbal Learning Test, were used to assess verbal memory. Visual Reproduction I and II and Rey-Osterrieth complex figure test, were employed to assess visuospatial memory. Measurements of width of granule cell layer (GCL) and neuronal cells count were performed on ImageJ software. The average width of GCL was measured in each surgical case on NeuN stained section. Neuronal cell counts in all epilepsy tissue and control specimens were analyzed according to Blumcke et al. (2007) Values of neuronal cell counts from each hippocampal subfield were transformed into z-scores. Student`s t test was used to analyze the importance of clinical data; p values <0.05 were considered as statistical significant. Results: GCD was observed in 28 cases (51.9%): 14 in right and 14 in left MTLE. Clinical variables, different patterns of MTS and postoperative outcome were similar between GCD and no-GCD groups in right and left MTLE. Visuospatial memory was significantly affected in right MTLE GCD group when compared to the no-GCD group. However, in left MTLE-MTS group presence of GCD was not associated with memory performance. Conclusions: GCD was not correlated with clinical variables, MTS type and seizure outcome. The occurrence of GCD was associated with visuospatial memory deficit in right MTLE patients. However, the presence of GCD was not associated with memory performance in left GCD group. The present findings emphasize the importance of performing histopathology evaluation as part of surgery epilepsy protocol, and its contribution in the understanding of memory performance in TLE patients. However, the role of GCD in memory function is yet to be precisely defined.