Success rates for epilepsy surgery are well known. Until recently, success following surgery was defined primarily in terms of seizure reduction. However, more attention is now placed on the inclusion of cognitive and behavioral functioning as primary defining features of epilepsy and as important factors considered within the definition of surgical outcome. With that in mind, it has been determined that a cognitive “price” is paid by up to 40% of patients undergoing surgery, regardless of the resulting level of seizure control. It is thus important for surgical treatment teams to have effective methods of determining which surgical candidates are at risk for paying this important price, so that effective preventative strategies can be developed and implemented.
What we know thus far is that the rate of memory decline is highest in patients undergoing left (dominant) temporal lobe resections. The primary approach to identifying risk for memory decline has been to evaluate the presurgical functional status of the lobe to be resected, with a greater degree of postoperative memory impairment observed in those individuals with the highest level of presurgical functioning. To date, the functional integrity of the temporal lobe has been evaluated through a variety of methods, including the Wada test and both structural and functional imaging methods, with varying levels of success in using those data for predicting postsurgical memory outcome. A number of studies have also examined the predictive use of presurgical neuropsychological testing in multivariate models combined with other clinically relevant variables.