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Katsushige Watanabe, Takashi Watanabe, Akio Takahashi, Nobuhito Saito, Masafumi Hirato and Tomio Sasaki

✓ The feasibility of high-frequency transcranial electrical stimulation (TES) through screw electrodes placed in the skull was investigated for use in intraoperative monitoring of the motor pathways in patients who are in a state of general anesthesia during cerebral and spinal operations.

Motor evoked potentials (MEPs) were elicited by TES with a train of five square-wave pulses (duration 400 µsec, intensity ≤ 200 mA, frequency 500 Hz) delivered through metal screw electrodes placed in the outer table of the skull over the primary motor cortex in 42 patients. Myogenic MEPs to anodal stimulation were recorded from the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The mean threshold stimulation intensity was 48 ± 17 mA for the APB muscles, and 112 ± 35 mA for the TA muscles. The electrodes were firmly fixed at the site and were not dislodged by surgical manipulation throughout the operation. No adverse reactions attributable to the TES were observed.

Passing current through the screw electrodes stimulates the motor cortex more effectively than conventional methods of TES. The method is safe and inexpensive, and it is convenient for intraoperative monitoring of motor pathways.

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Naoki Ikegaya, Akio Takahashi, Takanobu Kaido, Yuu Kaneko, Masaki Iwasaki, Nobutaka Kawahara and Taisuke Otsuki

Surgical treatment of the insula is notorious for its high probability of motor complications, particularly when resecting the superoposterior part. Ischemic damage to the pyramidal tract in the corona radiata has been regarded as the cause of these complications, resulting from occlusion of the perforating arteries to the pyramidal tract through the insular cortex. The authors describe a strategy in which a small piece of gray matter is spared at the bottom of the periinsular sulcus, where the perforating arteries pass en route to the pyramidal tract, in order to avoid these complications. This method was successfully applied in 3 patients harboring focal cortical dysplasia in the posterior insula and frontoparietal operculum surrounding the periinsular sulcus. None of the patients developed permanent postoperative motor deficits, and seizure control was achieved in all 3 cases. The method described in this paper can be adopted for functional preservation of the pyramidal tract in the corona radiata when resecting epileptogenic pathologies involving insular and opercular regions.

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Akio Morita, Shigeo Sora, Mamoru Mitsuishi, Shinichi Warisawa, Katopo Suruman, Daisuke Asai, Junpei Arata, Shoichi Baba, Hidechika Takahashi, Ryo Mochizuki and Takaaki Kirino

Object. To enhance the surgeon's dexterity and maneuverability in the deep surgical field, the authors developed a master—slave microsurgical robotic system. This concept and the results of preliminary experiments are reported in this paper.

Methods. The system has a master control unit, which conveys motion commands in six degrees of freedom (X, Y, and Z directions; rotation; tip flexion; and grasping) to two arms. The slave manipulator has a hanging base with an additional six degrees of freedom; it holds a motorized operating unit with two manipulators (5 mm in diameter, 18 cm in length). The accuracy of the prototype in both shallow and deep surgical fields was compared with routine freehand microsurgery. Closure of a partial arteriotomy and complete end-to-end anastomosis of the carotid artery (CA) in the deep operative field were performed in 20 Wistar rats. Three routine surgical procedures were also performed in cadavers.

The accuracy of pointing with the nondominant hand in the deep surgical field was significantly improved through the use of robotics. The authors successfully closed the partial arteriotomy and completely anastomosed the rat CAs in the deep surgical field. The time needed for stitching was significantly shortened over the course of the first 10 rat experiments. The robotic instruments also moved satisfactorily in cadavers, but the manipulators still need to be smaller to fit into the narrow intracranial space.

Conclusions. Computer-controlled surgical manipulation will be an important tool for neurosurgery, and preliminary experiments involving this robotic system demonstrate its promising maneuverability.

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Takanobu Kaido, Taisuke Otsuki, Akiyoshi Kakita, Kenji Sugai, Yoshiaki Saito, Takafumi Sakakibara, Akio Takahashi, Yuu Kaneko, Yuko Saito, Hitoshi Takahashi, Ryoko Honda, Eiji Nakagawa, Masayuki Sasaki and Masayuki Itoh

Object

Some patients are not seizure free even after epileptogenic cortical resection. The authors recently described a case of frontal lobe epilepsy cured after the resection of periventricular white matter and striatum, in which dysplastic neurons were revealed. The authors attempted to confirm similar cases.

Methods

They reviewed the records of 8 children with frontal lobe epilepsy who had daily (7) or monthly (1) seizures and underwent resections including deep brain structures.

Results

Five patients underwent multiple resections. Neuroimaging of the deep structures showed the transmantle sign in 3 patients, ictal hyperperfusion in 6, reduced iomazenil uptake in 2, and spike dipole clustering in 6. All patients became seizure free postoperatively. Focal cortical dysplasia of various types was diagnosed in all patients. Dysmorphic neurons were found in the cortex and subcortical white matter of 5 patients. The striatum was verified in 3 patients in whom dysmorphic neurons were scattered. In the periventricular white matter, prominent astrocytosis was evident in all cases.

Conclusions

Pathological abnormalities such as dysmorphic neurons and astrocytosis in deep brain structures would play a key role in epileptogenesis.

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Fumio Yamaguchi, Hirotomo Ten, Tadashi Higuchi, Tomoko Omura, Toyoyuki Kojima, Koji Adachi, Takayuki Kitamura, Shiro Kobayashi, Hiroshi Takahashi, Akira Teramoto and Akio Morita

Intraoperative 3D recognition of the motor tract is indispensable to avoiding neural fiber injury in brain tumor surgery. However, precise localization of the tracts is sometimes difficult with conventional mapping methods. Thus, the authors developed a novel brain mapping method that enables the 3D recognition of the motor tract for intrinsic brain tumor surgeries. This technique was performed in 40 consecutive patients with gliomas adjacent to motor tracts that have a risk of intraoperative pyramidal tract damage. Motor tracts were electrically stimulated and identified by a handheld brain-mapping probe, the NY Tract Finder (NYTF). Sixteen-gauge plastic tubes were mounted onto the NYTF and inserted in the estimated direction of the motor tract with reference to navigational information. Only the NYTF was removed, leaving the plastic tubes in their places, immediately after muscle motor evoked potentials were recorded at the minimum stimulation current. Motor tracts were electrically identified in all cases. Three-dimensional information on the position of motor tracts was given by plastic tubes that were neurophysiologically placed. Tips of tubes showed the resection limit during tumor removal. Safe tumor resection with an arbitrary safety margin can be performed by adjusting the length of the plastic tubes. The motor tract positioning method enabled the 3D recognition of the motor tract by surgeons and provided for safe resection of tumors. Tumor resections were performed safely before damaging motor tracts, without any postoperative neurological deterioration.

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Naoki Ikegaya, Masaki Iwasaki, Yuu Kaneko, Takanobu Kaido, Yuiko Kimura, Tetsuya Yamamoto, Noriko Sumitomo, Takashi Saito, Eiji Nakagawa, Kenji Sugai, Masayuki Sasaki, Akio Takahashi and Taisuke Otsuki

OBJECTIVE

Cognitive risk associated with insular cortex resection is not well understood. The authors reviewed cognitive and developmental outcomes in pediatric patients who underwent resection of the epileptogenic zone involving the insula.

METHODS

A review was conducted of 15 patients who underwent resective epilepsy surgery involving the insular cortex for focal cortical dysplasia, with a minimum follow-up of 12 months. The median age at surgery was 5.6 years (range 0.3–13.6 years). Developmental/intelligence quotient (DQ/IQ) scores were evaluated before surgery, within 4 months after surgery, and at 12 months or more after surgery. Repeated measures multivariate ANOVA was used to evaluate the effects on outcomes of the within-subject factor (time) and between-subject factors (resection side, anterior insular resection, seizure control, and antiepileptic drug [AED] reduction).

RESULTS

The mean preoperative DQ/IQ score was 60.7 ± 22.8. Left-side resection and anterior insular resection were performed in 9 patients each. Favorable seizure control (International League Against Epilepsy class 1–3) was achieved in 8 patients. Postoperative motor deficits were observed in 9 patients (permanent in 6, transient in 3). Within-subject changes in DQ/IQ were not significantly affected by insular resection (p = 0.13). Postoperative changes in DQ/IQ were not significantly affected by surgical side, anterior insular resection, AED reduction, or seizure outcome. Only verbal function showed no significant changes before and after surgery and no significant effects of within-subject factors.

CONCLUSIONS

Resection involving the insula in children with impaired development or intelligence can be performed without significant reduction in DQ/IQ, but carries the risk of postoperative motor deficits.

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Sho Kobayashi, Yukihiro Matsuyama, Kenichi Shinomiya, Shigenori Kawabata, Muneharu Ando, Tsukasa Kanchiku, Takanori Saito, Masahito Takahashi, Zenya Ito, Akio Muramoto, Yasushi Fujiwara, Kazunobu Kida, Kei Yamada, Kanichiro Wada, Naoya Yamamoto, Kazuhiko Satomi and Toshikazu Tani

Object

Although multimodal intraoperative spinal cord monitoring provides greater accuracy, transcranial electrical stimulation motor evoked potential (TcMEP) monitoring became the gold standard for intraoperative spinal cord monitoring. However, there is no definite alarm point for TcMEPs because a multicenter study is lacking. Thus, based on their experience with 48 true-positive cases (that is, a decrease in potentials followed by a new neurological motor deficit postoperatively) encountered between 2007 and 2009, the authors set a 70% decrease in amplitude as the alarm point for TcMEPs.

Methods

A total of 959 cases of spinal deformity, spinal cord tumor, and ossification of the posterior longitudinal ligament (OPLL) treated between 2010 and 2012 are included in this prospective multicenter study (18 institutions). These institutions are part of the Japanese Society for Spine Surgery and Related Research monitoring working group and the study group on spinal ligament ossification. The authors prospectively analyzed TcMEP variability and pre- and postoperative motor deficits. A 70% decrease in amplitude was designated as the alarm point.

Results

There were only 2 false-negative cases, which occurred during surgery for intramedullary spinal cord tumors. This new alarm criterion provided high sensitivity (95%) and specificity (91%) for intraoperative spinal cord monitoring and favorable accuracy, except in cases of intramedullary spinal cord tumor.

Conclusions

This study is the first prospective multicenter study to investigate the alarm point of TcMEPs. The authors recommend the designation of an alarm point of a 70% decrease in amplitude for routine spinal cord monitoring, particularly during surgery for spinal deformity, OPLL, and extramedullary spinal cord tumor.