Association of Piriform Cortex Resection With Surgical Outcomes in Patients With Temporal Lobe Epilepsy

Abstract

Does resecting the piriform cortex improve surgical outcome in temporal lobe epilepsy? In this multicenter study that included 107 adults with temporal lobe epilepsy in the derivation cohort and 31 in the validation cohort, resecting a larger proportion of the piriform cortex (78% in seizure-free vs 46% in non–seizure-free cases in pooled data) was significantly associated with a favorable outcome. Removal of at least half the piriform cortex significantly increased the odds of becoming seizure free by a factor of 16. These findings support including the piriform cortex in standard anterior temporal lobe resections to achieve seizure freedom. This multicenter cohort study assesses outcomes of piriform cortex resection among patients with temporal lobe epilepsy. A functional area associated with the piriform cortex, termed area tempestas , has been implicated in animal studies as having a crucial role in modulating seizures, but similar evidence is limited in humans. To assess whether removal of the piriform cortex is associated with postoperative seizure freedom in patients with temporal lobe epilepsy (TLE) as a proof-of-concept for the relevance of this area in human TLE. This cohort study used voxel-based morphometry and volumetry to assess differences in structural magnetic resonance imaging (MRI) scans in consecutive patients with TLE who underwent epilepsy surgery in a single center from January 1, 2005, through December 31, 2013. Participants underwent presurgical and postsurgical structural MRI and had at least 2 years of postoperative follow-up (median, 5 years; range, 2-11 years). Patients with MRI of insufficient quality were excluded. Findings were validated in 2 independent cohorts from tertiary epilepsy surgery centers. Study follow-up was completed on September 23, 2016, and data were analyzed from September 24, 2016, through April 24, 2018. Standard anterior temporal lobe resection. Long-term postoperative seizure freedom. In total, 107 patients with unilateral TLE (left-sided in 68; 63.6% women; median age, 37 years [interquartile range {IQR}, 30-45 years]) were included in the derivation cohort. Reduced postsurgical gray matter volumes were found in the ipsilateral piriform cortex in the postoperative seizure-free group (n = 46) compared with the non–seizure-free group (n = 61). A larger proportion of the piriform cortex was resected in the seizure-free compared with the non–seizure-free groups (median, 83% [IQR, 64%-91%] vs 52% [IQR, 32%-70%]; P  < .001). The results were seen in left- and right-sided TLE and after adjusting for clinical variables, presurgical gray matter alterations, presurgical hippocampal volumes, and the proportion of white matter tract disconnection. Findings were externally validated in 2 independent cohorts (31 patients; left-sided TLE in 14; 54.8% women; median age, 41 years [IQR, 31-46 years]). The resected proportion of the piriform cortex was individually associated with seizure outcome after surgery (derivation cohort area under the curve, 0.80 [ P  < .001]; external validation cohorts area under the curve, 0.89 [ P  < .001]). Removal of at least half of the piriform cortex increased the odds of becoming seizure free by a factor of 16 (95% CI, 5-47; P  < .001). Other mesiotemporal structures (ie, hippocampus, amygdala, and entorhinal cortex) and the overall resection volume were not associated with outcomes. These results support the importance of resecting the piriform cortex in neurosurgical treatment of TLE and suggest that this area has a key role in seizure generation.