Subtraction ictal single-photon emission computed tomography coregistered to magnetic resonance imaging in evaluating the need for repeated epilepsy surgery

Object. The aim of this study was to determine whether ictal single-photon emission computed tomography (SPECT) is useful in localizing the site of seizure onset in patients in whom surgery for intractable epilepsy failed and who are being considered for repeated surgery. Methods. Subtraction ictal SPECT coregistered to magnetic resonance imaging (SISCOM) studies were retrospectively analyzed in 58 patients who were being evaluated for possible repeated resection for intractable partial epilepsy between January 1, 1996, and October 31, 1999. All patients had persistent seizures subsequent to an initial resection and underwent another excision. The SISCOM-demonstrated abnormalities were classified as concordant, discordant, or indeterminate, compared with the localization of the epileptogenic zone revealed on video electroencephalography monitoring. The ability of SISCOM to predict operative outcome was also determined in patients who had undergone repeated surgical procedures. The SISCOM studies revealed a localized hyperperfused alteration in 46 (79%) of 58 patients. Forty-one (89%) of these 46 patients had a SISCOM-demonstrated alteration in the hemisphere of the previous epilepsy surgery. Imaging changes in 33 (72%) of the 46 patients were at the site of the previous focal cortical resection. Eight (17%) of the 46 had SISCOM-demonstrated abnormalities remote from the lobe in which surgery had been performed but in the ipsilateral hemisphere. The hyperperfusion focus was in the contralateral hemisphere in the remaining five patients (11%). The site of the epileptogenic zone was concordant with the SISCOM focus in 32 (70%) of 46 patients. Twenty-six patients underwent repeated resection and were followed up for a mean of 44 months thereafter; 11 of these patients (42%) had a significant reduction in seizure tendency. Only five patients (19%) were seizure free. Ten (50%) of 20 patients with a concordant SISCOM focus compared with none (0%) of three patients with a discordant focus had a favorable surgical outcome (p = 0.23). Conclusions. The SISCOM method might be useful in the evaluation of, and the surgical planning for, patients with intractable partial epilepsy in whom previous resective treatment has failed and who are being considered for reoperation.