Postoperative Recovery of Hippocampal Contralateral Diffusivity in Medial Temporal Lobe Epilepsy

Abstract

Summary:Purpose: To search for a recovery after surgery of mean diffusivity (MD) values in the contralateral nonsclerotic hippocampus of patients with medial temporal lobe epilepsy (MTLE) and hippocampal sclerosis (HS).Methods: Twenty-four MTLE patients (12 right-sided and 12 left-sided MTLE) and 36 healthy volunteers were investigated using diffusion tensor imaging. A region-of-interest approach was used to measure pre-and postoperative interictal hippocampal MD values in patients.Results: Diffusion abnormalities in contralateral nonsclerotic hippocampus recovered after surgery (p < 0.0001). A subgroup of 14 patients exhibited a clear increase in MD values whereas the remaining 10 patients were stable. No significant difference was found between the two subgroups for each of the electroclinical data studied including early postoperative outcome, all patients being either seizure free or with rare persistent auras.Conclusions: This finding suggests that diffusion abnormalities in contralateral hippocampus may represent a functional mechanism linked to the active epileptic process. Key Words: Diffusion tensor imaging-Medial temporal lobe epilepsy-Hippocampal sclerosis-Epilepsy surgeryRecovery.Using interictal diffusion tensor imaging (DTI) in medial temporal lobe epilepsy (MTLE) patients with hippocampal sclerosis (HS), we recently demonstrated bilateral hippocampal diffusion abnormalities: an increased mean diffusivity (MD) in the epileptic hippocampus and a decreased MD in the contralateral nonsclerotic hippocampus (Thivard et al., 2005). These bilateral diffusion abnormalities were uncorrelated with clinical variables including the duration and severity of the disease.A decrease in contralateral MD supports a bilateral hippocampal involvement in MTLE, in agreement with previous electroclinical, neuroradiological, and pathological data (Spencer, 1998). Proton magnetic resonance spectroscopy suggests that contralateral abnormalities may reflect neuronal dysfunction rather than cell loss since spectroscopic abnormalities tend to normalize in the postoperative period (Hugg et al., 1996;Cendes et al., 1997;Serles et al., 2001;Vermathen et al., 2002 Based on these findings, we hypothesized that the contralateral MD decrease found in our population might correspond to a functional impairment and thus might tend to normalize after surgery. We tested this hypothesis by measuring MD and FA values in hippocampal regions of MTLE patients. Contralateral diffusion abnormalities were determined before and after surgery and were correlated with clinical factors including the postoperative outcome. METHODS Patients and controlsThe study population included 24 patients (16 women and 8 men, mean age at surgery 31.9 years ± 8.9, range 20 to 50 years) with MTLE undergoing a complete presurgical evaluation at the epilepsy unit of the Salpêtrière hospital. The control group included 36 healthy volunteers (14 women and 22 men, mean age: 32.8 years ± 9.3, range 18 to 57 years).Unilateral HS was diagnosed from qualitative MRI assessmen...

Postoperative recovery of hippocampal contralateral diffusivity in medial temporal lobe epilepsy correlates with memory functions

“…Subsequently, we showed that the reduced MD in the contralateral hippocampus recovers after epilepsy surgery 2. This result supports previous proton magnetic resonance spectroscopy studies showing that spectroscopic abnormalities tend to normalise in the postoperative period 3–6.…”

“…It has been previously reported that patients with right MTLE are impaired in verbal memory before surgery, and this impairment is associated with a global decrease in left hemisphere functional activity 12. Furthermore, the MD in the left hippocampus of right-sided MTLE patients is reduced before surgery and returns to normal after surgery 1 2. Although several explanatory hypotheses have been previously proposed,2 the functional mechanisms leading to the recovery of MD remain speculative.…”

Advances in neuroimaging in patients with epilepsy

“…26,61,126 The significance of the contralateral changes is unclear and there is as yet no consensus as to whether these changes are reversible. Thivard et al 127 have found that diffusion abnor-…”

Functional Reorganization Associated with Semantic Language Processing in Temporal Lobe Epilepsy Patients after Anterior Temporal Lobectomy : A Longitudinal Functional Magnetic Resonance Image Study

“…Recent studies of a computer simulation 10) and DTI study 17) of TLE patents suggest that it may be possible to reverse some of the deleterious effect of epileptic seizures by surgical intervention. For left and right mTLE patients, we found that BOLD (blood-oxygenation level dependent) activation of the left PFC was abnormal pre-operatively, that the magnitude of the activation was negatively correlated with epileptic duration pre-operatively, and that the BOLD activation was normalized and recovered from the deleterious effects of epileptic seizures after surgery.…”

“…A recent diffusion tensor imaging (DTI) study of mTLE patients with HS suggests that hippocampal diffusion abnormalities are located bilaterally pre-operatively 16) , but the hippocampus contralateral to the lesion may recover after epilepsy surgery 17) . Consi-dering that the hippocampal system is an integral component of the brain circuit responsible for learning and retrieving linguistic facts and conventions 15) , if the contralateral hippocampus recovered from the active seizure process after successful surgery, we would expect that it would have a key role in inducing brain reorganization for language function in mTLE patients.…”