Abstracts

Rationale: Interictal PET and ictal subtraction SPECT scans of the brain have been shown to be valuable tests in the detection of seizure foci in patients with medically intractable epilepsy. The authors describe their experience with the use and comparison of such scans in the evaluation of patients for epilepsy surgery. Methods: Between 2003 and 2009, clinical information on all patients at our institution undergoing intracranial EEG monitoring was charted in a prospectively recorded database. Patients who underwent interictal PET and ictal subtraction SPECT prior to intra-cranial EEG were selected from this database. Patient characteristics and the findings on PET and ictal subtraction SPECT scans were analyzed. Sensitivity for detection of seizure foci with each imaging modality was compared; with the results of intracranial EEG monitoring being treated as the gold standard for localization. Results: Fifty-three patients underwent intracranial EEG monitoring with pre-operative interictal PET and ictal subtraction SPECT scans. The average age was 32.7 years (median 32 years, range 1-60 years). Twenty seven patients were female. Twenty-four patients had findings of focally reduced metabolism on interictal PET scan. All 53 patients studied demonstrated at least one region of relative hyperperfusion on ictal subtraction SPECT. Intracranial EEG monitoring identified a single seizure focus in 45 patients, with 41 eventually undergoing resective surgery. Among the 45 patients in whom a seizure focus was localized, PET scan showed hypometabolism in the same region in 25 (56% sensitivity). Ictal SPECT scan showed hyperperfusion in the same region in 39 patients (87% sensitivity). Intracranial EEG was concordant with at least one imaging study in 41 cases (91%) and with both studies in 23 cases (51%). In 16 out of 20 cases (80%) where PET did not correlate with intracranial EEG, the SPECT study was concordant. Conversely, PET and intracranial EEG were concordant in 2 out of the 6 cases (33%) where SPECT did not demonstrate the seizure focus outlined by intracranial EEG. Conclusions: Interictal PET and ictal subtraction SPECT studies can provide important information in the pre-operative evaluation of medically intractable epilepsy. SPECT is more sensitive, but when both studies are used together they provide complementary information. Such information guides the placement of intracranial electrodes and improves the sensitivity for detection of seizure foci.