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  • Author or Editor: Kazunari Yoshida x
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Ryosuke Tomio, Takenori Akiyama, Takayuki Ohira and Kazunari Yoshida

OBJECTIVE

The aim of this study was to determine the most effective electrode montage to elicit lower-extremity transcranial motor evoked potentials (LE-tMEPs) using a minimum stimulation current.

METHODS

A realistic 3D head model was created from T1-weighted images. Finite element methods were used to visualize the electric field in the brain, which was generated by transcranial electrical stimulation via 4 electrode montage models. The stimulation threshold level of LE-tMEPs in 52 patients was also studied in a practical clinical setting to determine the effects of each electrode montage.

RESULTS

The electric field in the brain radially diffused from the brain surface at a maximum just below the electrodes in the finite element models. The Cz-inion electrode montage generated a centrally distributed high electric field with a current direction longitudinal and parallel to most of the pyramidal tract fibers of the lower extremity. These features seemed to be effective in igniting LE-tMEPs.

Threshold level recordings of LE-tMEPs revealed that the Cz-inion electrode montage had a lower threshold on average than the C3–C4 montage, 76.5 ± 20.6 mA and 86.2 ± 20.6 mA, respectively (31 patients, t = 4.045, p < 0.001, paired t-test). In 23 (74.2%) of 31 cases, the Cz-inion montage could elicit LE-tMEPs at a lower threshold than C3–C4.

CONCLUSIONS

The C3–C4 and C1–C2 electrode montages are the standard for tMEP monitoring in neurosurgery, but the Cz-inion montage showed lower thresholds for the generation of LE-tMEPs. The Cz-inion electrode montage should be a good alternative for LE-tMEP monitoring when the C3–C4 has trouble igniting LE-tMEPs.

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Raita Fukaya, Kazunari Yoshida, Takenori Akiyama and Takeshi Kawase

The origin of moyamoya disease remains unknown. The onset of the angiographically apparent changes of typical moyamoya disease occurs in childhood, but de novo development of the disease has not been confirmed angiographically. The authors report on a case of de novo development of moyamoya disease in a middle-aged female whose cerebral angiography demonstrated no abnormal findings 5 years previously. To the best of the authors' knowledge, this case is the first reported instance of de novo development of definite moyamoya disease verified angiographically. This case demonstrates that the de novo development of moyamoya disease in a middle-aged adult did in fact occur, and angiographically visible features of the disease took < 5 years to complete.

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Ryosuke Tomio, Takenori Akiyama, Masahiro Toda, Takayuki Ohira and Kazunari Yoshida

OBJECTIVE

Transcranial motor evoked potential (tMEP) monitoring is popular in neurosurgery; however, the accuracy of tMEP can be impaired by craniotomy. Each craniotomy procedure and changes in the CSF levels affects the current spread. The aim of this study was to investigate the influence of several craniotomies on tMEP monitoring by using C3–4 transcranial electrical stimulation (TES).

METHODS

The authors used the finite element method to visualize the electric field in the brain, which was generated by TES, using realistic 3D head models developed from T1-weighted MR images. Surfaces of 5 layers of the head (brain, CSF, skull, subcutaneous fat, and skin layer) were separated as accurately as possible. The authors created 5 models of the head, as follows: normal head; frontotemporal craniotomy; parietal craniotomy; temporal craniotomy; and occipital craniotomy. The computer simulation was investigated by finite element methods, and clinical recordings of the stimulation threshold level of upper-extremity tMEP (UE-tMEP) during neurosurgery were also studied in 30 patients to validate the simulation study.

RESULTS

Bone removal during the craniotomy positively affected the generation of the electric field in the motor cortex if the motor cortex was just under the bone at the margin of the craniotomy window. This finding from the authors' simulation study was consistent with clinical reports of frontotemporal craniotomy cases. A major decrease in CSF levels during an operation had a significantly negative impact on the electric field when the motor cortex was exposed to air. The CSF surface level during neurosurgery depends on the body position and location of the craniotomy. The parietal craniotomy and temporal craniotomy were susceptible to the effect of the changing CSF level, based on the simulation study. A marked increase in the threshold following a decrease in CSF was actually recorded in clinical reports of the UE-tMEP threshold from a temporal craniotomy. However, most frontotemporal craniotomy cases were minimally affected by a small decrease in CSF.

CONCLUSIONS

Bone removal during a craniotomy positively affects the generation of the electric field in the motor cortex if the motor cortex is just under the bone at the margin of the craniotomy window. The CSF decrease and the shifting brain can negatively affect tMEP ignition. These changes should be minimized to maintain the original conductivity between the motor cortex and the skull, and the operation team must remember the fluctuation of the tMEP threshold.

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Yohei Kitamura, Takenori Akiyama, Hikaru Sasaki, Yuichiro Hayashi and Kazunari Yoshida

Meningiomas rarely cause CSF dissemination, and CSF seeding to the optic nerve (ON) is extremely rare. This is the first report of 2 cases of atypical meningioma with subacute visual loss due to ON seeding. The authors present the genetic characteristics of these atypical meningiomas with CSF dissemination. The patient in Case 1 was a 36-year-old woman with a 1.5-cm mass within the left ON, and the patient in Case 2 was a 70-year-old woman with a 0.9-cm mass around the right ON. Both individuals had undergone multiple surgeries for primary lesions and local recurrent lesions. They presented with subacute visual loss, and both tumors were completely resected. The pathological diagnosis was atypical meningioma with high MIB-1 indices and p53-positive cell ratios in each case. Comparative genomic hybridization showed significant chromosomal copy number alterations similar to the results of previous surgeries, confirming that the tumors were disseminated lesions. The present findings suggest that genetic characteristics, such as 1p and 10qcen-23 losses and 17q and 20 gains, shared by the 2 cases might be associated with CSF dissemination of meningiomas.