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Koki Shimoji, Michiko Matsuki and Hiroyuki Shimizu

✓ The evoked spinal electrogram (SEG) in man was recorded from the epidural space, applying the technique of continuous epidural block, and compared with cord dorsum potential (CDP) in wakeful rabbits. Wave-form characteristics of the evoked SEG's activated by the segmental nerves were almost the same in both cervical and lumbar regions. Somatosensory evoked response from the scalp was clearly demonstrated by stimulation of both the tibial nerve and fifth toe skin, whereas the evoked SEG was produced only by stimulation of the former. This finding might indicate that large nerve fibers are more responsible for producing the evoked SEG. Central latencies to the peaks of the second components of the P2 wave were 29 to 33 and 42 to 48 msec, in cervical and lumbar enlargements, respectively. This probably indicates the presence of a long feedback loop producing the second components. The amplitude of the N1 wave showed a steeper decline along the spinal cord than that of the P2 deflection, indicating the different origins of these two components. Polarity of both the N1 and P2 waves became reversed when the recording electrode was situated in the anterior epidural space. The wave-form characteristics of the evoked SEG in man were very similar to those of the CDP in wakeful rabbits.

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Koki Shimoji, Hiroyuki Shimizu and Yoichi Maruyama

✓ Somatosensory evoked response from the cervical skin surface over the spine (the cervical SER) was recorded, and compared with the cord dorsum potential (CDP) simultaneously recorded from the posterior epidural space at the same segment. The cervical SER evoked by segmental nerve stimulation consisted of an initially positive spike (P1), the peak latency being the same as that of the P1 of the CDP, followed by a smaller negative wave with two peaks. The latency of the second peak of the negative wave (N1) coincided with that of the N1 of the CDP. Subsequent to this negative wave, a slow positive wave (P2) with peak latency similar to that of the P2 of the CDP, could be noticed in some subjects. The cervical SER could not be evoked even by strong stimulation of the cauda equina. Thus, the cervical SER might reflect a segmental phenomenon rather than the conducted potential along the cord, and originate from the spinal root and cord in the same way as the segmentally evoked CDP.

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Phyo Kim, Buichi Ishijima, Hiroshi Takahashi, Hiroyuki Shimizu and Masayuki Yokochi

✓ The case is reported of a patient with progressive left hemiparesis due to vascular compression of the medulla oblongata. Metrizamide computerized tomography cisternography revealed that the left vertebral artery was compressing and distorting the left lateral surface of the medulla. Compression was surgically relieved and symptoms improved postoperatively. Neurological and symptomatic considerations are discussed in relation to the topographical anatomy of the lateral corticospinal tract.

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Michiharu Morino, Hiroyuki Shimizu, Kenji Ohata, Kiyoaki Tanaka and Mitsuhiro Hara

Object. Functional hemispherectomy, itself a modification of anatomical hemispherectomy, has been further modified to a less invasive method (hemispherotomy), in which cortical resection is minimized and the rest of the affected hemisphere is functionally isolated by transecting its projection and commissural fibers. Although descriptions of three different types of hemispherotomy procedures have been published, the authors believe that it is important to develop a common and universally acceptable method based on a systematic analysis of topographic anatomy and neuronal connections. To this end, they have analyzed the three aforementioned procedures on the basis of meticulous fiber dissections in previously frozen formalin-fixed human brains.

Methods. The brain anatomy pertinent to surgical hemispherotomy is described in conjunction with dissection studies in 14 previously frozen, formalin-fixed human brains. The anatomical landmarks necessary for performing particular neuronal fiber resections are identified, and their relationships with operative methods are discussed, with an emphasis on commonalities among the three hemispherotomy procedures.

Conclusions. In this analysis the authors confirmed that hemispherotomy typically consists of four common procedures: 1) interruption of the internal capsule and corona radiata; 2) resection of the medial temporal structures; 3) transventricular corpus callosotomy; and 4) disruption of the frontal horizontal fibers. After meticulous dissection of cadavers, the authors have designated a reliable method for performing these four operations that may be applicable as a commonly used procedure.

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Atsushi Koike, Hiroyuki Shimizu, Ichiro Suzuki, Buichi Ishijima and Morihiro Sugishita

✓ It has been widely accepted that the right temporal lobe plays a major role in the processing of music. One of the main lines of evidence was derived from Milner's study, published in 1962, which reported that right temporal lobectomy led to a decline in patient scores on four of the six subtests (Tonal Memory, Timbre, Loudness, and Time subtests) of the Seashore Measures of Musical Talents. That finding had led some surgeons and patients to hesitate in choosing right temporal lobectomy as a treatment for intractable epilepsy. The authors examined performance on the Seashore Measures before and after operations in 20 patients with right temporal lobectomy and nine patients with left temporal lobectomy. No disturbances in the Seashore Measures were detected after temporal lobectomy on either side. The extent of these temporal lobectomies was smaller than that of the temporal lobectomies in Milner's study, as measured along the sylvian fissure (1.5–4 cm; mean 2.7 cm, standard deviation (SD) 0.92 cm) and the base of the temporal lobe (3.5–5.5 cm; mean 4.7 cm, SD 0.63 cm). These findings indicate that the region resected on right temporal lobectomy in the present study is not essential for basic musical processing.

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Atsushi Koike, Hiroyuki Shimizu, Ichiro Suzuki, Buichi Ishijima and Morihiro Sugishita

It has been widely accepted that the right temporal lobe plays a major role in the processing of music. One of the main lines of evidence was derived from Milner's study, published in 1962, which reported that right temporal lobectomy led to a decline in patient scores on four of the six subtests (Tonal Memory, Timbre, Loudness, and Time subtests) of the Seashore Measures of Musical Talents. That finding had led some surgeons and patients to hesitate in choosing right temporal lobectomy as a treatment for intractable epilepsy. The authors examined performance on the Seashore Measures before and after operations in 20 patients with right temporal lobectomy and nine patients with left temporal lobectomy. No disturbances in the Seashore Measures were detected after temporal lobectomy on either side. The extent of these temporal lobectomies was smaller than that of the temporal lobectomies in Milner's study, as measured along the sylvian fissure (1.5–4 cm; mean 2.7 cm, standard deviation (SD) 0.92 cm) and the base of the temporal lobe (3.5–5.5 cm; mean 4.7 cm, SD 0.63 cm). These findings indicate that the region resected on right temporal lobectomy in the present study is not essential for basic musical processing.

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Kensuke Kawai, Hiroyuki Shimizu, Akira Yagishita, Taketoshi Maehara and Kimiko Tamagawa

Object. Epilepsy in patients with bihemispheric malformations of cortical development (MCD) is typically medically intractable. Focal resection has been reported to be ineffective. Corpus callosotomy has been advocated as a treatment option, but the results have been reported only in several case reports. The authors describe a series of 10 patients with bihemispheric MCDs who underwent total corpus callosotomy.

Methods. The MCDs in these patients included lissencephaly, band heterotopia, perisylvian polymicrogyria, and tuberous sclerosis. Preoperatively all patients suffered disabling drop attacks or intense head drop seizures that caused frequent physical injuries. The follow-up period ranged from 1.4 to 5.8 years (median 3.2 years). Seizure outcome, parental assessment of daily function, and parental satisfaction with outcome were assessed postoperatively. Drop attacks disappeared completely during the entire follow-up period in eight patients and decreased to less than 10% of baseline in one. Other types of seizures were resolved completely in one patient and decreased in seven. Overall daily function improved and parents were satisfied with the surgery-related results in all patients except one who experienced a recurrence of drop attacks. There were no signs of significant and persistent neurological deficits in any case.

Conclusions. Results of total corpus callosotomy in patients with bihemispheric MCDs were favorable in most cases. The procedure was particularly effective against drop attacks causing physical injuries and impaired quality of life in these patients.

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Kazuya Motomura, Lushun Chalise, Fumiharu Ohka, Kosuke Aoki, Kuniaki Tanahashi, Masaki Hirano, Tomohide Nishikawa, Junya Yamaguchi, Hiroyuki Shimizu, Toshihiko Wakabayashi and Atsushi Natsume

OBJECTIVE

Lower-grade gliomas (LGGs) are often observed within eloquent regions, which indicates that tumor resection in these areas carries a potential risk for neurological disturbances, such as motor deficit, language disorder, and/or neurocognitive impairments. Some patients with frontal tumors exhibit severe impairments of neurocognitive function, including working memory and spatial awareness, after tumor removal. The aim of this study was to investigate neurocognitive and functional outcomes of frontal LGGs in both the dominant and nondominant hemispheres after awake brain mapping.

METHODS

Data from 50 consecutive patients with diffuse frontal LGGs in the dominant and nondominant hemispheres who underwent awake brain surgery between December 2012 and September 2018 were retrospectively analyzed. The goal was to map neurocognitive functions such as working memory by using working memory tasks, including digit span testing and N-back tasks.

RESULTS

Due to awake language mapping, the frontal aslant tract was frequently identified as a functional boundary in patients with left superior frontal gyrus tumors (76.5%). Furthermore, functional boundaries were identified while evaluating verbal and spatial working memory function by stimulating the dorsolateral prefrontal cortex using the digit span and visual N-back tasks in patients with right superior frontal gyrus tumors (7.1%). Comparing the preoperative and postoperative neuropsychological assessments from the Wechsler Adult Intelligence Scale–Third Edition (WAIS-III) and Wechsler Memory Scale–Revised (WMS-R), significant improvement following awake surgery was observed in mean Perceptual Organization (Z = −2.09, p = 0.04) in WAIS-III scores. Postoperative mean WMS-R scores for Visual Memory (Z = −2.12, p = 0.03) and Delayed Recall (Z = −1.98, p = 0.04) were significantly improved compared with preoperative values for every test after awake surgery. No significant deterioration was noted with regard to neurocognitive functions in a comprehensive neuropsychological test battery. In the postoperative course, early transient speech and motor disturbances were observed in 30.0% and 28.0% of patients, respectively. In contrast, late permanent speech and motor disturbances were observed in 0% and 4.0%, respectively.

CONCLUSIONS

It is noteworthy that no significant postoperative deterioration was identified compared with preoperative status in a comprehensive neuropsychological assessment. The results demonstrated that awake functional mapping enabled favorable neurocognitive and functional outcomes after surgery in patients with diffuse frontal LGGs.

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Hiroyuki Shimizu, Kazuya Motomura, Fumiharu Ohka, Kosuke Aoki, Kuniaki Tanahashi, Masaki Hirano, Lushun Chalise, Tomohide Nishikawa, Junya Yamaguchi, Jun Yoshida, Atsushi Natsume and Toshihiko Wakabayashi

OBJECTIVE

The current study aimed to evaluate the treatment outcomes and toxicities of patients with intracranial germ cell tumors (GCTs).

METHODS

This study retrospectively included 110 consecutive patients (70 patients in the germinomatous group and 40 patients in the nongerminomatous GCT [NGGCT] groups) receiving surgery, platinum-based chemotherapy, and radiotherapy for newly diagnosed primary intracranial GCTs. In the authors’ protocol, patients with GCTs were further divided into the following four groups: the germinomatous group and the NGGCT groups (mature teratoma, intermediate prognosis, or poor prognosis).

RESULTS

The median overall survival (OS) and progression-free survival (PFS) rates of the patients in the germinomatous group were significantly higher than those in the NGGCT group (p < 0.001). The 5-, 10-, and 20-year OS rates in the germinomatous group were 97.1%, 95.7%, and 93.2%, respectively, with a median follow-up of 11.0 years. On the contrary, the 5-, 10-, and 20-year OS rates in the NGGCT group were 67.3%, 63.4%, and 55.4%, respectively. The 5-, 10-, and 20-year PFS rates were 91.4%, 86.6%, and 86.6%, respectively, in the germinomatous group, whereas those of the NGGCT group were approximately 67.4%, 60.2%, and 53.5%, respectively. Based on the four types of classification in our study, the 5-, 10-, and 20-year OS rates in the NGGCT intermediate prognosis group were 78.9%, 71.8%, and 53.8%, respectively. On the contrary, the 3- and 5-year OS rates in the NGGCT poor prognosis group were 42.9% and 34.3%, respectively. Moreover, toxicities with the treatment of intracranial GCTs were found to be tolerable in the present study population. The multivariate survival models for OS in the NGGCT intermediate prognosis and poor prognosis groups demonstrated that only the alpha-fetoprotein status was significantly associated with worsened OS (HR 3.88, 95% CI 1.29–11.66; p = 0.02).

CONCLUSIONS

The authors found that platinum-based chemotherapy and radiotherapy result in favorable survival outcomes in patients with germinomatous GCTs. Clinical outcomes were still unfavorable in the NGGCT intermediate prognosis and poor prognosis groups; therefore, a new protocol that increases the survival rate of patients belonging in both groups should be considered.

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