COMPARISON OF ICTAL SPECT AND INTERICTAL PET IN THE PRESURGICAL EVALUATION OF TEMPORAL-LOBE EPILEPSY

We retrospectively compared ictal technetium 99m hexamethylpropyleneam ineoxime single-photon emission computed tomography (SPECT) and interi ctal F-18-fluorodeoxyglucose positron emission tomography (PET) in 35 patients with well-lateralized temporal lobe epilepsy (TLE). Based on SPECT scans the two observers correctly lateralized seizure foci with certainty in 89% of patients; interobserver agreement was excellent. B oth observers incorrectly lateralized the seizure focus on two SPECT s cans; one error was explained by rapid electroencephalographic spread to the contralateral side and for the other patient, isotope was injec ted during a brief aura. Based on PET scans, observers correctly later alized the foci with certainty in 63% and with lesser confidence in 83 %; four incorrect lateralizations were made by one observer and none b y the other. PET interobserver disagreement was explained by differenc es between observers in weighting the relative hypometabolism in media l and lateral temporal regions. The detection rate for PET was lower i n the absence of structural imaging abnormalities (60 vs 87%). PET yie lded correct lateralizations in the 2 patients for whom SPECT interpre tation was difficult. We conclude that both ictal SPECT and interictal PET are sensitive methods for the lateralization of TLE, but SPECT ca n be interpreted with greater certainty and is more sensitive when mag netic resonance imaging findings are negative. False lateralization is rare with ictal SPECT and can be explained when interpreted in conjun ction with electroclinical data. Both investigations have complementar y roles when localization is difficult.