Abstracts

Rationale: Hippocampal sclerosis (HS) is the commonest histopathology in drug-resistant mesial temporal lobe epilepsy (MTLE). HS types have been reliably related to post-operative outcome, with ILAE type 1 associated with better outcome. It is still necessary a presurgical brain imaging marker that can stratify patients according to postsurgical prognosis and which could be easily incorporated into pre-operative evaluation. The aim of this study was to compare histopathological patterns in sclerotic hippocampus with hippocampal volume obtained from brain structural imaging analyses. Methods: Cases were selected from the period of 2005 to 2014. Clinical data from epilepsy history were assessed pre-operatively. Seizure control was defined according to Engel's classification and the follow-up of one year was noted. One paraffin-embedded block of mid hippocampal body was selected for HS classification according to ILAE criteria into types 1, 2, 3 and no-HS. NeuN-immunoreactive cell bodies were counted within hippocampal subfields in four randomly visual fields and cell densities were transformed into z-score values. Brain structural imaging was performed with a 1.5T MRI system. FreeSurfer was used for subcortical and cortical volumetric estimation of the ipsilateral hippocampus. Univariate analysis of variance and Pearson's correlation test were applied for statistical analyses. Results: Sixty seven cases (36 female, 34 right HS) were included. ILAE type 1 HS was identified in 53 patients, type 2 in eight, type 3 in two and four had no HS. Of these, 50 patients had one year post-operative outcome evaluated. Complete seizure relief, i.e. Engel IA, was achieved in 65.0% of patients with ILAE type 1 HS and in 57.1% of type 2. No patient with type 3 (100% Engel IB) or no HS (100% Engel IIIA) was seizure free. Patients with ILAE type 1 and 2 had smaller hippocampal volumes (3151.7 ± 448.22 and 3215.3 ± 966.01 mm³, respectively) compared to patients with no-HS (4185.8 ± 669.83 mm³). Patients with ILAE type 3 had mean hippocampal volume (3857.5 ± 28.50 mm³) intermediate between type 1 and no-HS but not significant (p=0.074). Positive correlation was encountered between hippocampal volume and CA1, CA3, CA4 and total estimated neuronal densities. CA2 was the only sector which not correlated its neuronal density with imaging volume (p=0.415). Conclusions: This is the first study correlating hippocampal atrophy on MRI with ILAE patterns of HS and neuronal loss within each subfield, a fundamental finding to anticipate surgical prognosis for patients with drug-resistant MTLE and HS. Funding: This work was supported by FAPESP, CAPES and CNPq.