Subtle Microscopic Abnormalities in Hippocampal Sclerosis Do Not Predict Clinical Features of Temporal Lobe Epilepsy

Abstract

Summary:Purpose: Subtle microdysplastic features are found in some patients with hippocampal sclerosis (HS) and refractory temporal lobe epilepsy. The significance of these findings is unknown. We investigated their frequency, relation to the pattern of HS, and clinical associations.Methods: One-hundred forty patients with histologically confirmed HS (mean age at operation, 35 years; 85 women) were analyzed. The presence of HS and subtle structural abnormalities (SSAs) in the mesial temporal lobe and in the lateral neocortical tissue was assessed in detail. Antecedents, seizure characteristics, two verbal memory tests, and outcome in HS patients with and without SSAs were determined.Results: SSAs were found in 60 (43%) of the 140 HS patients, being mesial only in 32 of the 60 cases, and lateral only in nine cases; the remaining 19 cases had both mesial and lateral abnormalities. The frequency of SSA was not related to the pattern of HS or other tested variables. Prolonged febrile convulsions were present in 26 (44%) patients with SSAs, and in 26 (34%) patients (not significant) without SSAs. The outcome after surgery did not differ between patients with SSAs (incidence rate ratio for seizure recurrence, 0.9; 95% confidence interval, 0.5-1.6) compared with patients without SSAs (reference ratio, 1).Conclusions: Forty-three percent of HS patients have SSAs in their lobectomy specimens. The presence of SSAs does not predict clinical characteristics, such as presence of prolonged febrile convulsions, postsurgical outcome, or neuropsychological performance, nor does it correlate with the histologic pattern of HS.

Neuropathologic and Clinical Features of Human Medial Temporal Lobe Epilepsy

“…It has been suggested that this represents a preexisting susceptibility factor that renders the affected brain vulnerable to the development of mTLE after IPI or FS, but the reciprocal relationship remains unknown 43. Recent data show that microscopic cortical dysplasia is not related to clinical parameters such as IPI or FS, or to the histological characteristics of HS;43-45 our results are consistent with these previous findings. Hence, the role of microscopic cortical dysplasia is currently obscure, and future studies are needed to reveal the complexities.…”

“…Microscopic cortical dysplasia may appear in 20-45% of surgical specimens from mTLE patients with HS 43-45. We found microscopic cortical dysplasia in 11 patients (42.3%), a rate similar to that of previous reports, suggesting that it is a relatively commonly associated finding in HS.…”

Surgical Treatments for Epilepsy

“…There is an association with prolonged febrile convulsions in childhood, and in animal models such seizures can cause permanent hippocampal damage. However, human pathologic specimens often show ectopic neurons, raising the possibility that the damaged hippocampus was developmentally defective (Kalnins et al, 2004). Complications of temporal lobectomy can include a quadrantic visual field deficit, although this is very rare with a selective hippocampectomy.…”

Surgical and postmortem pathology studies: contribution for the investigation of temporal lobe epilepsy

“…In the recently proposed classification of FCD 77 , its association with MTS is classified as type IIIa. Dysplastic abnormalities, such as cortical laminar disorganization, presence of dysmorphic neurons, and balloon cells in the temporal neocortex of TLE-MTS patients have been described 78,79 , although their clinical relevance and role in the epileptogenesis in these patients remain undefined 80 . Simultaneous recording of the hippocampus and dysplastic abnormalities in the temporal neocortex with depth electrodes and subdural strips showed that even subtle dysplastic lesions are epileptogenic 72 .…”