Free Communications: Surgery

Abstract

Abstract Ictal SPECT in Supplementary Motor Area Seizure. 1 Masafumi Fukuda, 2 Hiroshi Masuda, 2 Junpei Honma, 2 Ayataka Fujimoto, 2 Shigeki Kameyama, and 1 Ryuichi Tanaka ( 1 Department of Neurosurgery, Brain Research Institute, University of Niigata 2 Department of Neurosurgery, Epilepsy Center, Nishi-Niigata-Chuo National Hospital, Niigata, Japan ). Purpose: The clinical semiology of supplementary motor area (SMA) seizures is characterized by abrupt, bilateral, tonic posturing of the extremities, vocalization, mostly preserved consciousness, and short duration. The SMA has multiple reciprocal connections with the primary sensorimotor cortex (SMC), anterior cingulate cortex (ACC), and various parietal somatosensory areas. Therefore, the epileptic discharges from SMA can rapidly propagate to these structures. In the present study, we used ictal SPECT to clarify the propagation pathways of epileptic discharges in patients with SMA seizures who were evaluated with chronic subdural electrodes for a definite localization of the seizure onset zone. Methods: We studied four patients (four males; age range, 18–27 years) with SMA seizures. The seizures occurred 1–10 times per day and lasted for 10–15 seconds. In two patients, proton magnetic resonance (MR) imaging revealed a hyperintense lesion indicative of focal cortical dysplasia (FCD) in the right SMA, where subdural electrode monitoring also localized the ictal onset. After complete resection of the FCD including the epileptic foci, these patients remained seizure free. In the other two patients, MR images were normal, but subdural electrode monitoring permitted verification of ictal onset in the left SMA. After partial resection of the SMA, including the epileptic foci, these patients experienced a significant (>90%) reduction of seizure frequency and were classified as class IIB outcome according to Engel's classification. SPECT studies were performed in all patients as a preoperative evaluation. Ictal SPECT was performed during seizures that occurred while the patients were undergoing inpatient video-EEG monitoring. The radioisotope 99mTc-ECD was injected immediately after seizure onset. The interval from seizure onset to the time of injection was no more than 3 seconds. Ictal and interictal SPECT images were acquired within 30 minutes after radioisotope injections. Regional cerebral blood flow (rCBF) measurements obtained under ictal and interictal conditions were compared on a voxel-by-voxel basis using the paired t-test option in SPM99. Images from the two patients with no lesions on MR images were reversed such that the hemisphere having epileptic foci appeared on the right. The changes were considered significant when the p-value was less than 0.001, uncorrected for multiple independent comparisons. Results: SPM analysis revealed significant increases of rCBF in bilateral ACC (x= 10, y=–6, z= 44 mm; Zmax= 4.97 and x=–18, y=–20, z= 42; Zmax= 4.49), the right globus pallidus (x= 20, y=–2, z= 2; Zmax= 4.23), and the cerebellar hemisphere (x=–26, y=–48, z=–38; Zmax= 4.22) in ictal condition. The right ACC contained a cluster with a submaximum in the right primary SMC (x= 36, y=–18, z= 46; Z= 4.35). No reduction in rCBF was observed in ictal condition. Conclusions: In patients with SMA seizures, hyperperfusion areas depicted on ictal SPECT did not localize within the SMA but spread to the adjacent cortex such as ACC and SMC ipsilateral to the epileptic foci. Additionally, epileptic discharges propagated to remote areas such as the globus pallidus and cerebellum that have direct or indirect reciprocal connections with the SMA. We caution that in patients with SMA seizures, ictal SPECT localization is not always concordant with epileptogenic foci but reveals already spread seizure activities.