The promise of subtraction ictal SPECT co-registered to MRI for improved seizure localization in pediatric epilepsies: Affecting factors and relationship to the surgical outcome

Abstract

Objective Ictal SPECT is promising for accurate non-invasive localization of the epileptogenic brain tissue in focal epilepsies. However, high quality ictal scans require meticulous attention to the seizure onset. In a relatively large cohort of pediatric patients, this study investigated the impact of the timing of radiotracer injection, MRI findings and seizure characteristics on ictal SPECT localizations, and the relationship between concordance of ictal SPECT, scalp EEG and resected area with seizure freedom following epilepsy surgery. Methods Scalp EEG and ictal SPECT studies from 95 patients (48 males and 47 females, median age = 11 years, (25th, 75th) quartiles = (6.0, 14.75) years) with pharmacoresistant focal epilepsy and no prior epilepsy surgery were reviewed. The ictal SPECT result was examined as a function of the radiotracer injection delay, seizure duration, epilepsy etiology, cerebral lobe of seizure onset identified by EEG and MRI findings. Thirty two patients who later underwent epilepsy surgery had postoperative seizure freedom data at <1, 6 and 12 months. Results Sixty patients (63.2%) had positive SPECT localizations - 51 with a hyperperfused region that was concordant with the cerebral lobe of seizure origin identified by EEG and 9 with discordant localizations. Of these, 35 patients (58.3%) had temporal and 25 (41.7%) had extratemporal seizures. The ictal SPECT result was significantly correlated with the injection delay (p<0.01) and cerebral lobe of seizure onset (specifically frontal versus temporal; p = 0.02) but not MRI findings (p = 0.33), epilepsy etiology (p ≥ 0.27) or seizure duration (p = 0.20). Concordance of SPECT, scalp EEG and resected area was significantly correlated with seizure freedom at 6 months after surgery (p=0.04). Significance Ictal SPECT holds promise as a powerful source imaging tool for presurgical planning in pediatric epilepsies. To optimize the SPECT result the radiotracer injection delay should be minimized to ≤ 25 s, although the origin of seizure onset (specifically temporal versus frontal) also significantly impacts the localization.

Subtraction Ictal SPECT coregistered to MRI (SISCOM) as a guide in localizing childhood epilepsy

“…Overall, 16/44 (36.4%) patients were selected for resective surgery (twelve with temporal, four with frontal lesions). This is in line with other similar studies in which final selection for surgery was completed in almost one‐third of the patients entering the epilepsy surgery screening protocol (22%‐54%) . Of those undergoing surgery, both SISCOM and MRI were equally localizing the PEZ in 13/16 cases (81.3%).…”

“…Finally, temporal lobe localization of the PEZ correlated with better SISCOM outcomes, compared to extratemporal localizations (76.9% vs 42.1%). This ability of SISCOM to better localize temporal foci has already been reported in both adult and pediatric studies . Depending on their origin of onset among other factors, seizures may have different propagation patterns that can influence SISCOM outcome.…”

“…Injection delay is crucial for ictal SPECT outcome, and different studies have suggested better localizations when the radiotracer injection occurs within 30 seconds from seizure onset. 19,24 Noteworthy, injection time did not influence SISCOM outcome in this study, probably because it was performed within 30 seconds in nearly all patients. Similar results have been recently reported in a highly specialized pediatric center.…”

“…Subtraction ictal SPECT coregistered to MRI (SISCOM) is a high‐resolution imaging tool that provides high sensitivity and specificity localization of the seizure focus with a remarkable predictive value of good surgical outcome . SISCOM has been used with variable positive outcomes in adults, but large studies applied to the pediatric population are lacking . The scope of the present study is to assess the feasibility of SISCOM in a pediatric clinical setting and to determine whether it is useful to localize the presumed epileptogenic zone (PEZ) in children who are candidate for resective surgery.…”

“…15 SISCOM has been used with variable positive outcomes in adults, 7,[16][17][18] but large studies applied to the pediatric population are lacking. 19 The scope of the present study is to assess the feasibility of SISCOM in a pediatric clinical setting and to determine whether it is useful to localize the presumed epileptogenic zone (PEZ) in children who are candidate for resective surgery.…”