The cognitive consequence of resecting nonlesional tissues in epilepsy surgery--results from MRI- and histopathology-negative patients with temporal lobe epilepsy

Abstract

Purpose: Because more selective and individual versus extended standard surgery in the treatment of epilepsy appears to result in similar seizure outcomes, the issue of sparing nonlesional and hypothetically still-functioning tissues has become a central topic in epilepsy surgery. Within this framework we hypothesized that surgery in magnetic resonance imaging (MRI)- and histopathologically negative patients with temporal lobe epilepsy (TLE) may serve as a proof of principle about the negative cognitive consequences of resecting nonlesional tissue.

Methods: Verbal and figural memory outcomes after temporal lobe surgery in 15 MRI- and histopathologically negative patients (MRH-) were compared to those obtained in 15 MRI- and histopathologically positive patients (MRH+). In the MRH- group, 53% were male, 66% were resected on the left side, 13% underwent selective amygdalohippocampectomy, and 20% became seizure-free. MRH+ patients were selected from >1,000 TLE patients, and provided matched pairs in regard to chronological age, sex, IQ, attention performance, onset of epilepsy, side and type of surgery, age at surgery, and seizure outcome. Individual and combined standardized scores for verbal/figural memory were evaluated.

Key findings: Preoperatively, memory was significantly better and less frequently impaired in MRH- as opposed to MRH+ patients. Postoperatively, memory losses in MRH- were more severe as opposed to MRH+ patients who did not change, on average. Losses in individual test parameters were seen in between 27% and 80% in MRH- patients as compared to between 13% and 47% in MRH+ patients. After surgery, outcomes for both groups were at comparably poor performance levels.

Significance: Preoperative group differences in memory and the finding that, after surgery, both groups had comparably poor performance levels indicate a major relevance of morphologic structural lesions for memory impairment in TLE. The findings in particular confirm the negative impact of the resection of nonlesional functional tissue for cognitive surgical outcome. Absence of MRI lesion and unimpaired memory appear as significant risk factors for postoperative memory loss in temporal lobe surgery.