Makoto Oishi

Epileptic Spikes: Magnetoencephalography versus Simultaneous Electrocorticography

Summary:  Purpose: To test the sensitivity of extracranial magnetoencephalography (MEG) for epileptic spikes in different cerebral sites.

Single and Multiple Clusters of Magnetoencephalographic Dipoles in Neocortical Epilepsy: Significance in Characterizing the Epileptogenic Zone

Summary:  Purpose: To characterize the epileptogenic zone in neocortical epilepsy (NE) by using magnetoencephalography (MEG).

Surgical strategy and outcomes for epileptic patients with focal cortical dysplasia or dysembryoplastic neuroepithelial tumor.

Summary:  Purpose: The purpose of this study was to clarify and compare the influence of surgical strategy on relief from seizures in patients with focal cortical dysplasia (FCD) and those with dysembryoplastic neuroepithelial tumor (DNT).

Facial nerve motor-evoked potential monitoring during skull base surgery predicts facial nerve outcome

Objective: To determine whether monitoring facial nerve motor-evoked potentials (FNMEPs) elicited by transcranial electrical stimulation during skull base tumour surgery is useful for predicting facial nerve outcome. Methods: This study analysed FNMEP findings in 26 patients with skull base tumours. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supramaximal stimuli (180–550 V). FNMEPs were recorded from the orbicularis oculi and oris muscles. The correlation between the final-to-baseline FNMEP ratio and postoperative facial nerve function was examined. Results: Postoperative facial nerve function correlated significantly with the FNMEP ratios in the orbicularis oculi (p = 0.004) and orbicularis oris (p<0.001) muscles. An FNMEP ratio of <50% consistently predicted immediate postoperative facial palsy, although the degree of palsy differed among patients. All patients had satisfactory facial nerve function (House and Brackmann grades I and II) postoperatively if the FNMEP ratio remained at >50%. Conclusions: Intraoperative FNMEP monitoring can be useful for predicting facial nerve function after skull base surgery. This new method is a valuable adjunct to conventional facial nerve monitoring.

Magnetoencephalography in Patients with Tuberous Sclerosis and Localization-related Epilepsy

Summary:  Purpose: To clarify the usefulness of magnetoencephalography (MEG) for diagnosis of the spatial relations between spike foci and suspicious epileptogenic tubers on MRI in patients with tuberous sclerosis (TS) and to compare MEG spike foci with single‐photon emission computed tomography (SPECT) findings.

Stereotactic radiofrequency thermocoagulation for hypothalamic hamartoma with intractable gelastic seizures

Management of hypothalamic hamartoma with intractable gelastic epilepsy remains controversial. We have used stereotactic thermocoagulation for treatment of hypothalamic hamartoma with intractable gelastic epilepsy since 1997. Herein, we review our experience in five cases to clarify the usefulness of this treatment. A total of five patients with hypothalamic hamartoma were treated by stereotactic thermocoagulation at our hospital during the period October 1997 through February 2004. In all patients, the hamartoma was less than 10mm in diameter and was located on the floor of the third ventricle with sessile attachment to the wall. To identify ictal onset, chronic intracranial electroencephalography was performed in three patients with the use of a depth electrode implanted in the hamartoma. Attempts were made to induce gelastic seizure by electrical stimulation of the hamartoma in three patients. After magnetic resonance imaging-guided targeting, radiofrequency thermocoagulation of the boundary between the hamartoma and normal hypothalamus was performed to achieve disconnection effects. Marked reductions in seizure frequency were obtained in all cases, with three patients becoming seizure-free after the procedure. No intraoperative complications occurred except in one patient who experienced acute and transient panidrosis with hot flushes during coagulation. Our results suggest that stereotactic thermocoagulation of hypothalamic hamartoma is an acceptable treatment option for patients with intractable gelastic seizures.

Neurophysiologic findings of neuronal migration disorders : Intrinsic epileptogenicity of focal cortical dysplasia on electroencephalography, electrocorticography, and magnetoencephalography

We define specific neurophysiologic characteristics for focal cortical dysplasia, a neuronal migration disorder. We reviewed data from published reports and our patients with focal cortical dysplasia. Our patients underwent preoperative scalp video-electroencephalography (EEG), magnetic resonance imaging (MRI), magnetoencephalography, and intraoperative or extraoperative electrocorticography monitoring. Scalp EEG showed trains of rhythmic epileptiform spike or sharp waves. Positive spikes correlated with early seizure onset, MRI lesion around the rolandic fissure, hemiparesis, and a less favorable outcome. Interictal electrocorticography showed continuous epileptogenic discharges: repetitive electrographic seizures and bursting discharges or continuous or quasicontinuous rhythmic spiking. Ictal electrocorticography showed paroxysmal fast and/or repetitive spiking. Magnetoencephalography showed clustered spike sources within and extending from the lesion. Cortical stimulation gave more frequent, lower-threshold afterdischarges and higher-threshold primary motor function. Focal cortical dysplasias are highly and intrinsically epileptogenic. For surgical seizure control, EEG, electrocorticography, and magnetoencephalography must delineate the intrinsic epileptogenic zone within and extending from the focal cortical dysplasia identified by MRI. (J Child Neurol 2005;20:357—363).

Presurgical simulation with advanced 3-dimensional multifusion volumetric imaging in patients with skull base tumors.

BACKGROUND: Despite recent diagnostic and technical advancements in the field of neurosurgery, surgical treatment for tumors in the skull base region, ie, skull base tumors (SBTs), remains a challenge. OBJECTIVE: To validate the utility of presurgical simulation for the treatment of SBTs by 3-dimensional multifusion volumetric imaging (3D MFVI), including volume rendering and image fusion, to combine data from various imaging modalities. METHODS: We performed presurgical simulation using 3D MFVI for 21 SBTs (acoustic neurinomas, jugular neurinomas, meningiomas, chordomas, and others) in 20 patients. We collected targeted data from computed tomography, magnetic resonance imaging, computed tomography or magnetic resonance angiography, and digital subtraction angiography and combined these data using image-analyzing software. The simulations were used to assess the 3D relationships among the microsurgical anatomical components, the appropriate surgical approach, and the resectable parts of the tumor. Finally, we compared the results of the simulation with the operative results. RESULTS: In all patients, the 3D MFVI techniques enabled adequate visualization of the microsurgical anatomy and facilitated presurgical simulation, thereby allowing the surgeons to determine an appropriate and feasible surgical approach. All procedures to open the bone window were performed in accordance with the simulations, except for the surgical exposure of the acoustic canal for 2 acoustic neurinomas. In 3 of the 21 cases, tumor removal could not be performed according to the simulations because of unexpected bleeding or other restrictions. CONCLUSION: The 3D MFVI technique was of a sufficiently high quality to enable visualization of the 3D microsurgical anatomy. This promising method can facilitate determination of the most appropriate approach and safe and precise surgical procedures for SBTs.

Clinicopathological factors related to regrowth of vestibular schwannoma after incomplete resection

OBJECT The authors retrospectively analyzed various clinicopathological factors to determine which are related to regrowth during a long-term follow-up period in patients who underwent incomplete vestibular schwannoma (VS) resection. METHODS This study involved 74 patients (25 men and 49 women) in whom a VS was treated surgically via the lateral suboccipital approach, and who had postoperative follow-up periods exceeding 5 years. The mean follow-up was 104.1 months (range 60-241 months), and the mean patient age at surgery was 48.1 years (range 19-75 years). The tumors ranged in size from 0 mm (localized within the internal auditory canal) to 56 mm (28.3 ± 12.2 mm [mean ± SD]). RESULTS Gross-total resection (GTR) was performed in 41 (55%) of the 74 patients; subtotal resection ([STR]; 90-99%) in 25 (34%); and partial resection ([PR]; < 90%) in 8 (11%). Regrowth rates in the GTR, STR, and PR groups were 2.4% (1 of 41 cases), 52% (13 of 25), and 62.5% (5 of 8), respectively, and the times to regrowth ranged from 6 to 76 months (median 31.9 months). The regrowth-free survival curves differed significantly between the complete (GTR) and incomplete (STR and PR) resection groups. Eighteen (54.5%) of the 33 patients who underwent incomplete resection showed evidence of regrowth during follow-up. Univariate and multivariate analyses of various factors revealed that both the thickness of the residual tumor, based on MR imaging after surgery, and the MIB-1 index were positively related to residual tumor regrowth. The receiver operating characteristic curves, plotted for both the thickness of the residual tumor and the MIB-1 index, identified the optimal cutoff points for these values as 7.4 mm (sensitivity 83.3%, specificity 86.7%) and 1.6 (sensitivity 83.3%, specificity 66.7%), respectively. CONCLUSIONS Greater residual tumor thickness, based on MR imaging after the initial surgery, and a higher MIB-1 index are both important factors related to postoperative tumor regrowth in patients who have undergone incomplete VS resection. These patients require frequent neuroimaging investigation during follow-up to assure early detection of tumor regrowth.

Ictal magnetoencephalographic discharges from elementary visual hallucinations of status epilepticus

Purpose: To report the rare opportunity to study ictal magnetoencephalography (MEG) in a 26 year old man with simple partial status epilepticus that presented as elementary visual hallucinations (EVHs) in the right upper visual field. Methods: The patient described his EVHs as “snowing on TV,” “flickering lights,” and “rotating coloured balls” that continued for several days. MEG and simultaneous EEG were recorded twice: during an episode of EVHs (ictal recordings) and after EVHs were controlled by medications (interictal recordings). Results: During EVHs, MEG showed continuous periodic epileptiform discharges over the left posterior superior temporal region, while simultaneous EEG showed rhythmic theta waves and sporadic spikes over the left temporal region. The MEG discharge consisted of a three phase spike complex. Equivalent current dipoles (ECDs), modelled from spike complexes, localised in the left superior temporal area. After drug treatment controlled the EVHs, interictal MEG and EEG showed rare spikes over the same left temporal region. The average ictal ECD moment (mean (SD)) (128.7 (32.8 nAm)) was significantly weaker than the average interictal ECD moment (233.0 (63.9) nAm) (p<0.05). Conclusions: The continuous, periodic, and clustered discharges seen on ictal MEG were the sources of EVH. The weaker ictal ECD sources were frequently not detected by scalp EEG, while the stronger interictal sources, presumably originating from an extensive interictal zone, were sufficiently large to be seen as EEG spikes.