Abstracts

Rationale: Optimal surgical management of temporal lobe epilepsy (TLE) in patients with a normal appearing hippocampus (HC) on MRI is unclear. Research evaluating seizure and neuropsychological (NP) outcomes in this population is scarce, compromising adequate counseling of candidates for HC-sparing surgery. To address this issues, we retrospectively reviewed 152 patients (>=16 y.o.) who underwent TLE surgery at Cleveland Clinic from 2010 to 2018. Patients with MRI signs of hippocampal sclerosis (HS) or HS in pathology, and those with prior surgeries were excluded. Lesions outside of the HC were allowed. To address NP outcomes we compared measures of verbal memory, visual memory, and confrontation naming obtained around 6 months following surgery to those obtained before surgery. Methods: We measured HC volume using Neuroquant, FDA-cleared software for quantitative MRI analysis. We categorized resections as dominant or non-dominant based on handedness and/or language lateralization procedures. According to the type of resection, patients were classified into: spared-HC (n=74) or resected-HC (n=78). Kaplan-Meier estimates of longitudinal seizure-recurrence rates were obtained. Cox proportional-hazards models were stratified by type of resection and then combined into a single Cox-PH model. The final model estimating risk of seizure recurrence within 1 year of surgery was displayed as a nomogram. NP outcomes (n=86) were then classified as 'decline' or 'no decline' using epilepsy-specific reliable change indices. Results: Seizures recurred in around 40% of patients in the first year and in 63% within 6 years of surgery. There was no difference in the frequency of using invasive EEG between spared-HC (50%) vs resected-HC (47%) cohorts. At a univariate level, the following variables were associated with a higher risk of seizure recurrence: male (p=0.03), longer epilepsy duration (p<0.01), normal MRI (p=0.04), history of invasive evaluation (p=0.02), and acute post-up seizures (p<0.01). A higher although not statistically significant early seizure recurrence risk was observed in the spared-HC relative to the resected-HC, with equivalent long-term results (p=0.17) (Figure 1). The nomogram built with pre-operative variables estimates the risk of recurrent seizure within 1 year of surgery (Figure 2) with a bootstrap-validated concordance index of 0.64. On the dominant side (N=56), and when compared to resected-HC patients, those with spared-HC surgery had lower rates of clinically-meaningful declines in verbal memory (39.7% vs. 70.4%; p =0.03), and naming (40.7% vs. 79.2%; p =0.01). For the non-dominant surgeries (N=30), no significant difference was detected. Conclusions: Sparing a MRI-normal HC in TLE surgery may correlate with a higher risk of early seizure-recurrence, although long-term seizure outcomes seem equivalent. Although such a selective approach correlates with lower rates of short-term naming and verbal memory worsening, short-term declines still occur in around 40% of spared-HC patients, and their long-term memory and naming outcomes remain to be defined. We developed a potentially clinically-meaningful nomogram to facilitate clinical counseling. Funding: NIH grant - R01NS097719