Comparison of the diagnostic value of pet with EEG and MRI in patients with complex partial seizures

Interictal PET, by showing the changes in the cerebral glucosemetabolism, is a functional imaging modality used in the preoperative evaluationof intractable epilepsy patients. The purpose of the preoperative evaluation is tomake the decision for surgery by correctly localizing the epileptogenic zone, andto determine the area to be resected in order to gain seizure freedom.201 patients with intractable complex partial seizures were included in thisstudy. All patients underwent PET, routine EEG, video EEG monitoring (ictal andinterictal), MRI. MRS and invasive EEG monitoring was performed on some ofthe patients. In the operated lesional and nonlesional temporal lobe epilepsy(TLE) and frontal lobe epilepsy patients, the correlation of the results of thesediagnostic tests with the operation site was evaluated to determine whether thetests showed lobar concordance with the operation site. For the patients operatedfor VNS or for the patients not operated, the results of PET, MRI and interictalEEG were compared with the ictal EEG results for determining the lobarconcordance between them. In the evaluation of post-operative seizure outcome,Engel?s classification was used. The potential predictive factors for seizurefreedom were also evaluated.In the operated TLE group, interictal PET showed the highest lobarconcordance rate (%100) with the operation site, thus correctly localized theepileptogenic zone in all patients. ?ctal EEG, interictal EEG, MRI and MRSshowed lobar concordance rates of %98, %87, %83 and %54 respectively. PETshowed a %100 lobar concordance in both the lesional and non-lesional TLEgroups.Seizure freedom was achieved in %81 of the non-lesional TLE and %89 ofthe lesional TLE patients, and in both of these groups of patients there were nosignificant difference in the postoperative outcome. All of the lesional and non-lesional patients were either Engel class I or class II, meaning acceptable surgicaloutcome.The finding of bilateral temporal hypometabolism on PET was found to bethe only predictive factor for seizure freedom. The presence of unilateral temporalhypometabolism on PET increases the probability of seizure freedom 12 times,compared to the presence of bilateral temporal hypometabolism.In the patients operated for frontal lobe epilepsy, PET findings werecorrelated with the operation site in all of the patients, and all of these patientswere seizure free.Evaluations of the patients not operated were done in the TLE andextratemporal lobe epilepsy (ETLE) groups. In the TLE group, PET showed lobarconcordance with ictal EEG in %57 of the patients, while in the ETLE group thelobar concordance with icta EEG was %25. In the VNS patients, whom wereevaluated as not good candidates for resective surgery, all of the preoperative testswere mostly not concordant with ictal EEG.As a result, interictal PET not only localized the epileptogenic zone inlesional TLE, but also localized the epileptogenic zone correctly in the non-lesional TLE patients whose chance for being a candidate for surgery is ratherlower. The facts that there were no significant difference in the postoperativeoutcome of these two groups, and that more than %80 of the patients were seizurefree shows the role of PET in the decision making for surgery especially in thenon-lesional TLE patients. The relationship with PET findings showing nobilateral temporal hypometabolism and seizure freedom after surgery, points outthe role of PET in predicting postoperative outcome.