Summary:Purpose: To test the sensitivity of extracranial magnetoencephalography (MEG) for epileptic spikes in different cerebral sites.Methods: We simultaneously recorded MEG and electrocorticography (ECoG) by using subdural electrodes with 1-cm interelectrode distances for one patient with lateral frontal epilepsy and one patient with basal temporal epilepsy. We analyzed MEG spikes associated with ECoG spikes and compared the maximal amplitude and number of electrodes involved. We estimated and evaluated the locations and moments of the equivalent current dipoles (ECDs) of MEG spikes.Results: In patient 1, MEG detected 100 (53%) of 188 ECoG lateral frontal spikes, including 31 (46%) of 67 spikes that activated three subdural electrodes. MEG spike amplitudes correlated with ECoG spike amplitudes and the number of electrodes activated (p < 0.01). ECDs were perpendicular to the superior frontal sulcus. In patient 2, MEG detected 31 (26%) of 121 ECoG basal temporal spikes, but none that activated only three subdural electrodes. ECDs were localized in the entorhinal and parahippocampal gyri, oriented perpendicular to those basal temporal cortical surfaces. The ECD strength was 136.6 ± 71.5 nAm in the frontal region, but 274.5 ± 150.6 nAm in the temporal region (p < 0.01).Conclusions: When lateral frontal ECoG spikes extend >3 cm 2 across the fissure, MEG can detect >50%, correlating with spatial activation and voltage. In the basal temporal region, MEG requires higher-amplitude discharges over a more extensive area. MEG shows a significantly higher sensitivity to lateral convexity epileptic discharges than to discharges in isolated deep basal temporal regions. Key Words: Magnetoencephalography-Electrocorticography-Epilepsy-Extent of epileptic spikes-Sensitivity.Magnetoencephalography (MEG) measures the extracranial magnetic fields generated by intraneuronal electric currents with superconducting quantum interference devices (1). Extracranial magnetic fields result from intracranial tangential currents, such as neuronal activity, in the fissural cortex, which makes up two thirds of the surface of the human brain (2). During MEG analysis, magnetic field recordings are fitted to an equivalent current dipole (ECD) model to localize sources of intracranial activity, such as epileptic spikes; the spike source locations are then overlaid onto magnetic resonance (MR) images of corresponding areas of the brain. Because magnetic fields are relatively unaffected by the different electrical conductivities of the brain, cerebral spinal fluid, skull, and skin, MEG can accurately localize the source of intraneuronal electric currents that contribute to extracranial magnetic fields (3).Electroencephalography (EEG) dipole recordings delineate both radial and tangential currents (4). However, the electrical fields, as measured by EEG, are affected by the conductivities of different tissues.MEG has clinical application for patients with partial epilepsy. Neurosurgeons use advanced multisensor helmet-shaped, whole-head neuromagnetomete...

OBJECTIVE Spinal lipomas are generally thought to occur as a result of failed primary neurulation. However, some clinical features cannot be explained by this theory. The authors propose a novel classification of spinal lipomas based on embryonic changes seen during primary and secondary neurulation. METHODS A total of 677 patients with occult spinal dysraphism underwent 699 surgeries between August 2002 and May 2015 at the National Center for Child Health and Development and Tokyo Metropolitan Children's Medical Center. This group of patients had 378 spinal lipomas, including 119 conus spinal lipomas, 27 lipomyelomeningoceles, and 232 filum lipomas, which the authors classified into 4 types based on neural tube formation during embryonic development. Type 1 is defined as pure primary neurulation failure; Type 2 ranges from primary to secondary neurulation failure; Type 3 consists of secondary neurulation failure (early phase); and Type 4 is defined as secondary neurulation failure (late phase). The authors also review embryogenesis in secondary neurulation and analyze the clinical utility of the new classification. RESULTS There were 55 Type 1 spinal lipomas, 29 Type 2, 62 Type 3, and 232 Type 4. All filum lipomas fell into the Type 4 spinal lipoma category. Association with anorectal and/or sacral anomalies was seen in none of the Type 1 cases, 15 (52%) of Type 2, 35 (56%) of Type 3, and 31 (13%) of Type 4. Urogenital anomalies were observed in none of the Type 1 or Type 2 cases, 1 (2%) of Type 3, and 28 (12%) of Type 4. Anomaly syndromes were present in none of the Type 1 cases, 6 (21%) of Type 2, 3 (5%) of Type 3, and 16 (7%) of Type 4. Associated anomalies or anomaly syndromes were clearly observed only for Type 2–4 spinal lipomas encompassing failed secondary neurulation. Radical resection was feasible for Type 1 spinal lipomas. CONCLUSIONS Secondary neurulation of the spinal cord gives rise to the conus medullaris and filum terminale, which are often involved in spinal lipomas. Formation of spinal lipomas seems to be a continuous process overlapping primary and secondary neurulation in some cases. Association with other anomalies was higher in Type 2–4 spinal lipomas, which included failed secondary neurulation, than in Type 1 lipomas, with failed primary neurulation. On the other hand, radical resection was indicated for Type 1, but not for Type 2, spinal lipomas. The new classification of spinal lipomas based on embryonic stage has the potential for clinical use and agrees well with both clinical and surgical findings. The classification proposed here is still preliminary. Further studies and verification are necessary to establish its clinical utility.

Longstanding hydrocephalus and raised intracranial pressure can lead to unusual anatomical variants in the floor of the third ventricle, which may be important when performing endoscopic third ventriculostomy. Two middle aged patients with symptomatic longstanding hydrocephalus had scans that showed ventricular hydrocephalus, an empty sella, and a dilated infundibular recess which herniated into the sella turcica. Endoscopic third ventriculostomy confirmed that instead of the tuber cinerum and infundibular recess, the anterior inferior floor of the third ventricle was hanging down ventral to the pons into the sellar floor. Third ventriculostomy to the prepontine cistern was made on the dorsal wall of the dilated infundibular recess to the area surrounded by the dorsum sellae, the basilar artery trunk, and the left superior cerebellar artery, with good symptomatic control. Association of the empty sella and persistence of the infundibular recess must be carefully evaluated by MRI before attempting endoscopic third ventriculostomy. Herniation of the anterior inferior floor of the third ventricle into the empty sella can lead to loss of anatomical landmarks that require special attention during third ventriculostomy. (J Neurol Neurosurg Psychiatry 2000;69:531-534) Keywords: hydrocephalus; endoscopy; third ventriculostomy Endoscopic third ventriculostomy plays an important part in the treatment of hydrocephalus.1 Anatomical landmarks are well established and the procedure is safe in well experienced hands. Recently we have encountered two adult patients who were diagnosed as "long standing overt hydrocephalus in the adult (LOVA)" 2 and in whom the floor of the third ventricule was seen to be completely diVerent from the normal anatomy. We report the cases and surgical techniques, and discuss the relation between hydrocephalus, empty sella, and persistence of infundibular recess which were associated with the patients. CASE 1 A 31 year old woman had had chronic headaches, which increased in frequency and were accompanied by dizziness. Brain CT showed marked ventriculogmegaly with flat- Case report

For the last 25 years, it has been proven that the occurrence or recurrence of neural tube defects can be prevented with the administration of folic acid before and early pregnancy. At present, over 80 countries in the world, except Japan, have mandated the fortification of wheat flour and/or rice with folic acid, which has resulted in a significant reduction in the prevalence of neural tube defects. In 2000, the Japanese government recommended folic acid 400 μg daily for young women of childbearing age and women who are planning to conceive. In 2002, the government started to present information about the importance of folic acid in the development of fetuses in the Mother-Child Health Booklet annually. Despite these endeavors, the prevalence of neural tube defects has remained unchanged. We discuss the risk factors of neural tube defects and propose preventive measures to decrease the number of neonates with neural tube defects. We believe that the government should implement the fortification of staple food with folic acid very soon, which will eventually decrease not only the neonatal mortality and morbidity, but also the economic burden on our health care system.

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OBJECT The untethering of a tethered spinal cord in patients with a tight filum terminale is a relatively simple procedure that can prevent or improve neurological symptoms. Postoperatively, patients are usually kept in the horizontal decubitus position to prevent a CSF leak. However, the optimal period for keeping patients flat has not been determined yet. The authors compared 2 cohorts with different periods of horizontal decubitus; one with 72 hours and the other with 8 days. METHODS The authors retrospectively analyzed surgical results in 2 cohorts of pediatric patients who had tethered spinal cord with a tight filum terminale. One cohort was maintained flat for 8 days and the other cohort for 72 hours postoperatively. The patients' charts were reviewed for demographic data, clinical presentation, surgical therapy, and clinical course. RESULTS Three hundred fifty-four patients underwent sectioning of a tight filum terminale. Of those, 238 were kept lying flat for 8 days postoperatively, and 116 were maintained flat for 72 hours. Magnetic resonance imaging was performed 1 to 2 weeks after the surgery. None of the patients in either cohort developed a CSF leak. Pseudomeningocele, which was confirmed by MRI, developed in 1 patient who had been kept flat for 8 days. The occurrence rates of a CSF leak and pseudomeningocele were not significantly different in either cohort. CONCLUSIONS Keeping patients flat for longer than 72 hours did not change the rate of postoperative CSF leakage or pseudomeningocele. Seventy-two hours or less would be an appropriate period for maintaining patients flat after transection of a tight filum terminale.

The role of diffusion weighted imaging and apparent diffusion coefficient in intracranial germ cell tumors has not been fully elucidated. The aim of this study was to evaluate whether the ADC correlates with the histologic subtypes of germ cell tumors. We also aimed to investigate whether the ADC values can predict treatment response. The authors retrospectively analyzed the ADC values of the enhancing and solid regions of germ cell tumors. The absolute ADC values and the normalized ADC values were compared among different histologic diagnoses. The ADC values before and after the first course of chemotherapy were also compared between the different prognostic groups. Ten patients were included in the study. The median age at diagnosis was 9.3 years (range 5.3-13.8 years). There were four patients with germinoma and six patients with nongerminomatous germ cell tumor (NGGCT) including five mixed germ cell tumors and one immature teratoma. The mean absolute and normalized ADC values (×10(-3) mm(2)/s) were significantly lower in germinomas [0.835 ± 0.065 (standard deviation) and 1.11 ± 0.096, respectively] than in NGGCTs (1.271 ± 0.145 and 1.703 ± 0.223, respectively) (p = 0.01). The ADC values before and after the first course of chemotherapy were available in four patients. The ADC value after the first chemotherapy had a tendency to increase more in patients who eventually demonstrated complete response with chemotherapy than in patients who required second-look surgery. Assessment of the ADC values of germ cell tumors is considered to facilitate differentiation of histological subtypes of germ cell tumors. Evaluation of the ADC may also be useful for predicting treatment response.

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