Subtraction SPECT coregistered to MRI in focal malformations of cortical development: localization of the epileptogenic zone in epilepsy surgery candidates

PURPOSE: To determine the extent to which periictal subtraction single-photon emission computed tomography (SPECT) may improve detection and definition of the epileptogenic zone in patients with focal malformations of cortical development (MCDs). METHODS: Subtraction SPECT coregistered to magnetic resonance (MR) images (SISCOM) were constructed for 22 consecutive patients with focal MCDs who underwent periictal SPECT injection (18 ictal and four postictal). In the 17 patients who had epilepsy surgery, concordance between the site of SISCOM localization and site of surgical resection was determined by coregistration of SISCOM images with postoperative MRIs. RESULTS: SISCOM images were localizing in 19 (86%) patients, including eight of the 10 with nonlocalizing MRI. Concordance of SISCOM localization was 91% with MRI localization, 93% with scalp ictal EEG localization, and 100% with intracranial EEG localization. Eight patients whose SISCOM localization was concordant with the surgical resection site had lower postoperative seizure frequency scores (SFSs; p = 0.04) and greater postoperative improvement in SFSs (p = 0.05) than the nine patients whose SISCOM was either nonconcordant or nonlocalizing. On multiple regression analysis, a model combining SISCOM concordance with surgical resection site and extent of MRI lesion resection was predictive of postoperative SFS (R2 = 0.47; p = 0.03). CONCLUSIONS: Periictal subtraction SPECT using the SISCOM technique provides useful information for seizure localization in patients with focal MCDs, even when MRI is nonlocalizing.