Abstracts

RATIONALE: In presurgical evaluation of patients with epilepsy discordant results or non-lesional MRI might complicate diagnostic work up. Ictal SPECT especially when postprocessed with interictal SPECT and MRI (SISCOM) might be an additional useful diagnostic tool. We examined the prospective value of SISCOM in presurgical evaluation with either non-lesional MRI or discordant results in semiology, EEG-recordings, MRI and/or neuropsychological testing.
METHODS: 55 patients with medically intractable epilepsy undergoing presurgical evaluation were included. 26 patients showed no abnormalities in MRI, 5 patients showed a doubtful lesion only, 18 patients showed lesional MRI, and 6 underwent an epilepsy-surgical intervention before with unsatisfying outcome but postoperative MRI showed no abnormalites besides the postoperative defect. At least in those patients with lesional MRI, results of EEG, MRI, semiology and/or neuropsychological testing were discordant.
SPECT imaging was performed with a CERASPECT (Digital Scintigraphics, Inc., Waltham, MA) with a FWHM of 6-8 mm. The field of view diameter was 214 mm and the matrix size was 128 x 128 resulting in 64 images with cubic voxel dimensions of 1.67 mm. A 3D-T1 weighted MRI dataset was performed on a 1,5 T ACS-NT system (Philips, Best, The Netherlands). SISCOM was claculated with ANALYZE PC 3.0 software (Biomedical Imaging Resource, Mayo Foundation, Rochester, MN).
RESULTS: 64% showed a focal hyperperfusion, 24% a multifocal hyperperfusion and 13% could not be calculated because of insufficient quality of ictal SPECT e. g. due to movement artifacts. 25% of the results with focal hyperperfusion were localized in the insular, 34% were localized in the temporal lobe and 20% were localized in the frontal lobe.
In 11 patients intracranial electrodes were implanted according to the SISCOM results, 9 ECoG results were concordant to the SISCOM localization and two were discordant to SISCOM. In three patients with concordant and one with discordant ECoG/SISCOM results surgery could not be performed due to high risk or a too widespread seizure onset area.
In 13 patients who underwent surgery so far SISCOM was concordant/discordant to site of surgery in 10/1 of patients. In two patients who underwent surgery SISCOM could not be calculated.
CONCLUSIONS: In presurgical epilepsy-evaluation of difficult cases SISCOM can provide helpful additional information to create a successful hypothesis for intracranial electrode placement. Furthermore, as SISCOM localized in about 1/4 of cases with focal hyperperfusion to eloquent areas, it might also identify patients who are inoperable. However, as SISCOM is a very time- and manpower-consuming diagnostic tool, it can be offered to a restricted number of patients only. Further investigations are necessary to evaluate the value of the variables as for example significance of multifocal results, injection latency, duration of seizure, type of seizure, or test-retest reliability.