Importance: Surgery is an effective treatment for drug-resistant focal epilepsy. Neuroimaging studies are considered essential in the diagnostic evaluation of individuals with medically refractory focal seizures being considered for surgical treatment.
Objectives: To review the evidence for the use of neuroimaging studies in the selection of patients with drug-resistant temporal lobe epilepsy for focal cortical resection and discuss the prognostic importance of selected techniques.
Evidence review: Randomized clinical trials, meta-analyses, and clinical retrospective case studies (≥20 patients with ≥1 year of follow-up) were identified using Medical Subject Headings and indexed text terms in EMBASE (1988-November 29, 2014); MEDLINE (1946-December 2, 2014), Cochrane Central Register of Controlled Trials (1991-October 31, 2014), and Cochrane Database of Systematic Reviews (2005-October 31, 2014). Twenty-seven articles describing 3163 patients were included. Neuroimaging techniques analyzed included magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT). Subpopulations and prognostic factors were identified.
Findings: Of the 27 studies evaluated (3163 patients), 7 showed the outcome was more favorable in patients with MRI-identified hippocampal atrophy indicating mesial temporal sclerosis. Five additional studies indicated that the outcome was less favorable in patients with unremarkable MRI studies. There are conflicting findings regarding the prognostic importance of PET-identified focal hypometabolism; however, 2 investigations indicated that the presence of a PET imaging study demonstrating abnormalities in individuals with unremarkable MRI results showed an operative outcome similar to that in patients with mesial temporal sclerosis. The studies assessing SPECT use in temporal lobe epilepsy did not reveal a correlation with outcome.
Conclusions and relevance: There is strong evidence that preoperative MRI-identified hippocampal atrophy consistent with mesial temporal sclerosis concordant with the seizure origin in the temporal lobe is a significant factor associated with a favorable outcome. PET studies may be valuable in individuals with unremarkable MRI findings. The current evidence does not support the prognostic importance of SPECT in patients undergoing temporal lobe surgery.