Magnetoencephalogram in a postoperative case with a large skull defect
Harumi Yoshinaga1, Katsuhiro Kobayashi, Tohru Hoshida
1Department of Child Neurology, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan. magenta@md.okayama-u.ac.jp
Insights
Magnetoencephalography (MEG) successfully identified residual epileptogenic zones in a pediatric epilepsy patient, guiding further surgical intervention. This imaging technique proved crucial for detecting seizure sources missed by electroencephalography (EEG) due to a bone defect.
Area of Science:
- Neuroscience
- Epileptology
- Medical Imaging
Background:
- Congenital porencephaly can lead to refractory epilepsy.
- Accurate localization of epileptogenic zones is critical for successful epilepsy surgery.
- Electroencephalography (EEG) may face limitations in seizure source detection, especially with cranial bone defects.
Observation:
- A 12-year-old boy with congenital porencephaly presented with refractory seizures.
- Initial surgery for seizure control was partially successful, but residual seizures persisted.
- Magnetoencephalography (MEG) was utilized for presurgical and postsurgical evaluations.
Findings:
- Ictal MEG dipoles localized seizure activity to the left frontal lobe, correlating with intraoperative electrocorticography.
- Post-excision MEG identified residual epileptogenic zones missed by EEG due to a bone defect.
- Subsequent targeted re-excision led to a dramatic reduction in seizure frequency.
Implications:
- MEG is a valuable tool for localizing seizure foci in complex pediatric epilepsy cases.
- MEG can overcome limitations of EEG in patients with significant cranial bone defects.
- Successful surgical management of refractory epilepsy can be achieved with advanced neuroimaging guidance.
Abstract:
We present a patient in whom magnetoencephalograms were successfully performed in presurgical and postsurgical evaluations. A 12-year-old boy with congenital porencephaly was admitted with refractory adversive seizures and frontal absence seizures. Ictal magnetoencephalographic dipoles with frontal absence seizures were located in the left frontal lobe, anterior to the porencephalic cyst, and concordant with the same area detected by intraoperative electrocorticography. A partial cortical excision was performed, and the patient's cranial bone flap was removed because of an epidural abscess. The frontal absences then disappeared. The magnetoencephalogram revealed that secondary bilateral synchrony of focal discharges from the lesion may have caused the generalized seizures in this patient. Because of residual partial seizures, second and third magnetoencephalograms were performed, and we detected residual spike dipoles clustering in the area posterior to the cavity of cortical excision and anterior to the porencephalic cyst. Another excision of the area between the cavity and frontal edge of the cyst was performed, and seizure frequency diminished dramatically. In this case, despite the failure of dipole estimation by electroencephalogram in the context of a large bone defect, the magnetoencephalogram was useful in detecting the residual epileptogenic zone after failed epilepsy surgery.
