Neuropsychological outcomes after epilepsy surgery: systematic review and pooled estimates

Epilepsy surgery is a safe surgical procedure, but it may be associated with cognitive changes. Estimates of the risk of decline in specific neuropsychological domains after epilepsy surgery would assist surgical decision making in clinical practice. The goal of this study was to conduct a systematic review to derive pooled estimates of the rate of losses and gains in neuropsychological functions after epilepsy surgery, using empirically based methods for quantifying cognitive change.

An extensive literature search using PubMed, EmBase, and the Cochrane database was conducted, yielding 5,061 articles on epilepsy surgery, with 193 on neuropsychological outcomes (IQ, memory, language, executive functioning, attention, and subjective cognitive changes).

Of these, 23 met final eligibility criteria, with 22 studies involving temporal surgery only. Key aspects of inclusion criteria were N ≥ 20 and use of reliable change index or standardized regression-based change estimates. In addition to the proportion of patients experiencing losses and gains in each individual test, a single pooled estimate of gains and losses for each cognitive domain was derived using a random effects model. Weighted estimates indicated a risk to verbal memory with left-sided temporal surgery of 44%, twice as high as the rate for right-sided surgery (20%). Naming was reduced in 34% of left-sided temporal patients, with almost no patients with gains (4%). Pooled data on IQ, executive functioning, and attention indicated few patients show declines post surgery, but a substantial rate of improvement in verbal fluency with left-sided temporal surgery (27%) was found. Self-reported cognitive declines after epilepsy surgery were uncommon, and gains were reported in some domains where losses were found on objective tests (i.e., verbal memory and language). Variations in surgical techniques did not appear to have a large effect on cognitive outcomes, except for naming outcomes, which appeared better with more conservative resections. Sensitivity to postoperative changes differed across visual memory tests, but not verbal memory tests. Few conclusions could be made regarding cognitive risks and benefits of extratemporal epilepsy surgery, or of epilepsy surgery in children.

In sum, epilepsy surgery is associated with specific cognitive changes, but may also improve cognition in some patients. The results provide base rate estimates of expected cognitive gains and losses associated with epilepsy surgery that may prove useful in clinical settings.