Apparent diffusion coefficient of piriform cortex and seizure outcome in mesial temporal lobe epilepsy after MR-guided laser interstitial thermal therapy: a single-institution experience

Abstract

Objective: Piriform cortex (PC) is one of the critical structures in the epileptogenesis of mesial temporal lobe epilepsy (mTLE), but its role is poorly understood. The authors examined the utility of apparent diffusion coefficient (ADC; an MR-based marker of tissue pathology) of the PC as a predictor of seizure outcome in patients with mTLE undergoing MR-guided laser interstitial thermal therapy (MRgLITT).

Methods: A total of 33 patients diagnosed with mTLE who underwent MRgLITT at the authors' institution were included in the study. The 6-month postoperative seizure outcomes were classified using the International League Against Epilepsy (ILAE) system as good (complete seizure freedom, ILAE class I) and poor (seizure present, ILAE classes II-VI). The PC and ablation volumes were manually segmented from both the preoperative and intraoperative MRI sequences, respectively. The mean ADC intensities of 1) preablation PC; 2) total ablation volume; 3) ablated portion of PC; and 4) postablation residual PC were calculated and compared between good and poor outcome groups. Additionally, the preoperative PC volumes and proportion of PC volume ablated were examined and compared between the subjects in the two outcome groups.

Results: The mean age at surgery was 36.5 ± 3.0 years, and the mean follow-up duration was 1.9 ± 0.2 years. Thirteen patients (39.4%) had a good outcome. The proportion of PC ablated was significantly associated with seizure outcome (10.16 vs 3.30, p < 0.05). After accounting for the variability in diffusion tensor imaging acquisition parameters, patients with good outcome had a significantly higher mean ADC of the preablation PC (0.3770 vs -0.0108, p < 0.05) and the postoperative residual PC (0.4197 vs 0.0309, p < 0.05) regions compared to those with poor outcomes. No significant differences in ADC of the ablated portion of PC were observed (0.2758 vs -0.4628, p = 0.12) after performing multivariate analysis.

Conclusions: A higher proportion of PC ablated was associated with complete seizure freedom. Preoperative and postoperative residual ADC measures of PC were significantly higher in the good seizure outcome group in patients with mTLE who underwent MRgLITT, suggesting that ADC analysis can assist with postablation outcome prediction and patient stratification.

Keywords: apparent diffusion coefficient; diffusion tensor imaging; magnetic resonance–guided laser interstitial thermal therapy; mesial temporal epilepsy; piriform cortex.