Time Course of Postoperative Recovery of N‐Acetyl‐Aspartate in Temporal Lobe Epilepsy

Abstract

Summary Purpose: To assess the time course of increases in N‐acetyl‐aspartate/creatine (NAA/Cr), which can be measured using proton MR spectroscopic imaging (1H‐MRSI), in patients with intractable nonlesional temporal lobe epilepsy (TLE) after successful epilepsy surgery. Methods: We performed pre‐ and postoperative 1H‐MRSI in 16 seizure‐free (SF) patients and 16 not seizure‐free (NSF) TLE patients. We calculated a mixed‐design analysis of variance (ANOVA) between SF and NSF groups, ipsi‐ and contralateral to the side of operation, and pre‐ and postoperative NAA/Cr measurements. We applied nonlinear regression between pre‐ and postoperative NAA/Cr differences and the time interval between 1H‐MRSI scans to fit a negative exponential model to NAA recovery. Results: Mixed‐design ANOVA revealed that (a) postoperative NAA/Cr was significantly higher in SF than in NSF patients (p = 0.02) and that (b) in the SF group, postoperative NAA/Cr values were significantly higher than preoperative values (p <0.05) and returned to the normal range in most patients. According to our nonlinear regression model, in SF patients, there was a 50% increase relative to preoperative NAA/Cr values after 5.8 months, whereas an improvement of 95% was reached after 25 months. Conclusions: Our results extend preliminary observations of postoperative NAA recovery of SF patients by characterizing the time course of recovery as an exponential function with a half‐time of ∼6 months. The reversal of neuronal metabolic dysfunction remote from the epileptic focus may underlie the clinical observation of improvement of cognitive dysfunction after successful epilepsy surgery.