Addressing a Deep Problem With Magnetoencephalography

Temporal lobe encephaloceles: Electro-clinical characteristics and seizure outcome after tailored lesionectomy

OBJECTIVE

Our study aimed to investigate the management of patients with medically refractory epilepsy related to temporal encephaloceles, focusing on the use of ancillary testing in the pre-surgical evaluation to optimize surgical outcomes.

METHODS

We conducted a retrospective analysis of electronic medical records from the Cleveland Clinic, covering the period from January 2000 to May 2020. Patients with drug-resistant temporal lobe epilepsy were included if they had temporal lobe encephaloceles and required surgical intervention. We reviewed the results of ancillary studies, including invasive EEG.

RESULTS

A total of 19 patients with temporal lobe encephaloceles underwent resection for drug-resistant epilepsy treatment. Among them, 63 % reported experiencing auras commonly associated with mesial temporal lobe epilepsy, such as autonomic, psychic, and abdominal symptoms, followed by dialeptic seizures. Ictal patterns were consistently ipsilateral, with high amplitude delta or medium amplitude theta activity at onset, predominantly localized to the frontotemporal region in more than half of the cases. In 35 % of these patients, encephaloceles were only diagnosed during surgery. Stereo-EEG evaluation revealed two distinct ictal patterns: one characterized by localized low voltage fast activity in the temporal pole evolving into a 3-4 Hz high amplitude diffuse spiky activity, and the other exhibiting low amplitude rhythmic theta activity in the temporal pole with late involvement of the amygdala/hippocampus. Surgical resection strategy was based on clinical history and ancillary data analysis. At one-year follow-up after resection, 63 % of the patients attained Engel I seizure control over an average duration of 44 months (ranging from 6 months to 7.3 years). Additionally, 18 % of the patients achieved an Engel II outcome.

SIGNIFICANCE

Tailored resection of the encephalocele and the surrounding temporal pole, while preserving the mesial temporal structures, can effectively control seizures in patients with temporal encephaloceles identified through MRI. Patients presenting with temporal lobe symptoms and scalp ictal patterns characterized by polymorphic high delta theta activity with frontotemporal evolution should be evaluated for temporal encephaloceles as a potential underlying cause of their seizures, especially when the MRI is otherwise unrevealing.

Improving Detection of Hippocampal Epileptiform Activity Using Magnetoencephalography

PURPOSE

Magnetoencephalography (MEG) defines the spike-generating zone and provides targets for invasive monitoring with stereotactic electroencephalography. This retrospective, blinded, cross-sectional study determined whether MEG virtual sensors could identify hippocampal epileptiform activity.

METHODS

Using MEG beamformer analysis, virtual sensors were manually placed in bilateral hippocampi and corresponding virtual sensor waveforms were analyzed for the presence of epileptiform activity. These findings were compared with hippocampal stereotactic electroencephalography in the same patients. Concordance was determined using sensitivity and specificity.

RESULTS

Thirty patients (mean age 12.5 ± 5.9 years) and 35 hippocampi were included. Patients were also placed into subgroups based on conventional MEG analysis: temporal (n = 19), extratemporal (n = 10), and normal (n = 1). Overall, sensitivity and specificity were 57.9% and 50.0%, respectively (n = 35). Patients with temporal sources based on conventional MEG analysis had sensitivity and specificity of 80.0% and 36.4%, respectively (n = 21). Those with extratemporal sources based on conventional MEG had sensitivity and specificity of 42.9% and 80.0%, respectively (n = 12).

CONCLUSIONS

When grouped by conventional MEG analysis, virtual sensors can be useful to confirm mesial temporal dipoles seen with conventional analysis.

SIGNIFICANCE

This work may help support the use of MEG for the detection of epileptiform activity in the hippocampus and influence the planning of invasive electrode placement.