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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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Masakazu Takayasu, Masahito Hara, Katsuaki Yamauchi, Mitsuhiro Yoshida and Jun Yoshida

✓ Although atlantoaxial transarticular screw fixation is technically demanding and there is a significant risk of vertebral artery (VA) injury, transarticular screw insertion in the middle and lower cervical spine is simple and can be performed safely with the aid of lateral fluoroscopic guidance. The authors describe the surgical techniques and outcome of transarticular screw fixation in the middle and lower cervical spine.

Transarticular screw insertion into C2–3 or caudal cervical joints was performed from the articular pillar, directing the screw anterocaudally to penetrate the facet joint and the anterior cortex of the articular pillar, parallel to the sagittal plane. Because the VA and the nerve roots are anterior to the articular pillar at these levels, the screw can be placed safely with the assistance of lateral fluoroscopic guidance. Twenty-five patients ranging in age from 15 to 84 years underwent transarticular screw fixation, with a total of 81 screws. The transarticular screw was used as an anchor screw in combination with posterior cervical instrumentation in 19 patients and for facet screw fixation itself in six patients. Screw placement was successful and uncomplicated in all cases. The follow-up period ranged from 3 months to 5 years. No instance of screw backout or loosening was identified radiographically; fusion was achieved in all patients. Biomechanical strength is maintained by penetrating four cortical layers. When performed appropriately, this method is safe and reliable and deserves more widespread use.

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Mitsuhiro Hara, Chikafusa Kadowaki, Yoshifumi Konishi, Motohide Ogashiwa, Mitsuo Numoto and Kazuo Takeuchi

✓ An implantable device for measurement of cerebrospinal fluid (CSF) flow in a ventriculoperitoneal shunt tube has been developed. The unit is energized by an extracorporeal high-frequency generator (200 KHz), and electrolysis creates bubbles in the shunt tube. Velocity of bubble flow is detected by a pair of ultrasonic Doppler probes placed a certain distance apart on the skin surface and in parallel with the implanted tube. The CSF flow rate is calculated taking into account velocity and tube diameter, and is expressed in ml/min. The unit consists of a coil with a capacitor, a silicon diode to rectify the high frequency, and a Zener diode to regulate maximum output voltage of 20 V. The output is fed to a pair of platinum electrodes placed inside the unit's tunnel through which the CSF flows. These components are molded in epoxy resin and coated with medical-grade silicone rubber. In animal experiments, CSF flow rates ranging from 0.033 to 1.0 ml/min could be measured by this flowmeter. Clinically, CSF flow has been measured to date in several cases. In two cases of communicating hydrocephalus occurring after the onset of cerebrovascular disease, and in which the CSF flow was continuously monitored for 24 hours, the flow rate ranged between 0.05 and 0.78 ml/min. The CSF flow rate fluctuates in a 24-hour period, increasing in the morning, especially between 12 midnight and 6 a.m., which suggests a circadian rhythm.

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Toshihiro Takami, Kenji Ohata, Misao Nishikawa, Takeo Goto, Yuzo Terakawa, Yuichi Inoue, Kenichi Wakasa and Mitsuhiro Hara

✓ The authors discuss the utility of anterior transposition of the oculomotor nerve from the lateral wall of the cavernous sinus to widen the corridor posterior to the cisternal segment of the oculomotor nerve; this allows exposure of the anterolateral surface of the midbrain. This additional exposure was successfully used for the resection of a large calcified cavernoma in the upper brainstem of a 67-year-old woman who had presented with sudden onset of left hemiparesis and oculomotor palsy. The patient's postoperative course was uneventful and she displayed symptomatic improvement.

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Takeo Goto, Kenji Ohata, Toshihiro Takami, Misao Nishikawa, Akimasa Nishio, Michiharu Morino, Naohiro Tsuyuguchi and Mitsuhiro Hara

Object. The authors evaluated an alternative method to avoid postoperative posterior tethering of the spinal cord following resection of spinal ependymomas.

Methods. Twenty-five patients with spinal ependymoma underwent surgery between 1978 and 2002. There were 16 male and nine female patients whose ages at the time of surgery ranged from 14 to 64 years (mean 41.8 years). The follow-up period ranged from 6 to 279 months (mean 112.4 months). In the initial 17 patients (Group A), the procedure to prevent arachnoidal adhesion consisted of the layer-to-layer closure of three meninges and laminoplasty. In the subsequently treated eight patients (Group B), the authors performed an alternative technique that included pial suturing, dural closure with Gore-Tex membrane—assisted patch grafting, and expansive laminoplasty. In Group A, postoperative adhesion was radiologically detected in eight cases (47%), and delayed neurological deterioration secondary to posterior tethering of the cord was found in five cases. In Group B, there was no evidence of adhesive posterior tethering or delayed neurological deterioration. A significant intergroup statistical difference was demonstrated for radiologically documented posterior tethering (p < 0.05, Fisher exact test). Moreover, patients with radiologically demonstrated posterior tethering suffered a significant delayed neurological functional deterioration (p < 0.01, Fisher exact test).

Conclusions. This new technique for closure of the surgical wound is effective in preventing of postoperative posterior spinal cord tethering after excision of spinal ependymoma.

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Takeo Goto, Kenji Ohata, Michiharu Morino, Toshihiro Takami, Naohiro Tsuyuguchi, Akimasa Nishio and Mitsuhiro Hara

Object

The authors evaluated their surgical experience over 20 years with 14 treated falcotentorial meningiomas.

Methods

In the past 20 years, 14 patients with falcotentorial junction meningiomas were surgically treated. There were seven men and seven women, whose ages ranged from 34 to 79 years. On the basis of neuroimaging studies, the authors analyzed the influence of the anatomical relationship of the tumor to the vein of Galen, patency of the vein of Galen, tumor size, and the signal intensities on the magnetic resonance images to determine possible difficulties that might be encountered during surgery and to prognosticate the outcome of surgery. Depending on the relationship with the vein of Galen, tumors were labeled as either a superior or an inferior type. All tumors were resected via an occipital transtentorial approach.

The surgical outcome in eight patients was excellent; in the remaining six patients, it was fair. Of the prognostic factors, tumor location especially seemed to be the most important (p < 0.01, Fisher exact test). The outcome associated with the inferior type of tumor was significantly less optimal probably due to the relationship to the deep veins and the brainstem. In this series, the occlusion of deep veins did not significantly influence outcome.

Conclusions

Classification of the tumor location by preoperative neuroimaging studies can be helpful in estimating the surgical difficulty that might be encountered in treating the falcotentorial junction meningioma.

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Takeo Goto, Naohiro Tsuyuguchi, Kenji Ohata, Tsuyoshi Tsutada, Hideji Hattori, Masahiro Shimogawara, Yasuhiro Matusaka, Sinichi Sakamoto and Mitsuhiro Hara

Object. Objective assessment of sensory function disorders is difficult. In the present study, the authors investigated the possibility of assessing cervical myelopathy—induced sensory disorders by using magnetoencephalography (MEG) to measure somatosensory evoked magnetic fields (SSEMFs).

Methods. In 12 patients with cervical myelopathy, SSEMFs were measured before and after surgery by using a 160-channel helmet-type MEG system to stimulate the median nerve, and the intensity and latency of N20m (first response occurring 20 msec after stimulation) were then determined. Additionally, the severity of the sensory disorder was assessed before and after surgery by obtaining sensory scores determined using the Neurosurgical Cervical Spine Scale. Furthermore, in 11 healthy individuals (control group), the intensity and latency of N20m were measured in the same fashion. Analysis of the results showed that the preoperative intensity of N20m in the 12 patients with cervical myelopathy was significantly lower than that demonstrated in the control patients (p < 0.005, Student t-test). In addition, of six patients in whom sensory scores improved postoperatively, there were significant increases in the intensity of N20m (p < 0.005, paired t-test). Furthermore, there was a significant correlation between sensory scores and dipole intensity (p < 0.001, Spearman correlation coefficient by rank test).

Conclusions. Somatosensory evoked magnetic field measurements determined by MEG are useful in objectively and noninvasively assessing sensory disorders caused by cervical myelopathy.

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Takeo Goto, Kenji Ohata, Toshihiro Takami, Misao Nishikawa, Naohiro Tsuyuguchi, Michiharu Morino, Yasuhiro Matusaka, Akimasa Nishio, Yuichi Inoue and Mitsuhiro Hara

Object. The authors describe a new surgical technique for cervical laminoplasty that was performed in 25 patients. The posterior elements along with the various ligaments are removed en bloc and are stabilized in a lift-up position by placing hydroxyapatite (HA) laminar spacers and titanium miniplates and screws. The procedure and clinical results are discussed.

Methods. The posterior spinal elements, including the lamina(e), spinous process(es), and various attached ligaments, are removed en bloc by incising the lamina in its lateral aspect. Trapezoid-shaped HA spacers are placed between the cut ends of the laminae or between the laminae and lateral masses bilaterally at each level. Malleable titanium miniplates and screws are used for fixation of the spacers. The fixation of transected laminae was judged to be successful. Postoperative care included application of a soft neck collar for 1 week but no further restriction of activity. Surgery-related outcome was assessed in the 21 patients who attended more than 6 months of follow up after laminoplasty. There were 18 men and three women who ranged in age from 27 to 81 years. Cervical stenotic myelopathy was demonstrated in 15 patients who underwent decompressive and expansive laminoplasty, and spinal tumors were documented in six patients who underwent a nonexpansive laminoplasty. Postoperative and follow-up computerized tomography scans demonstrated no hardware failure. Bone formation around the spacers was observed either at 6- or at 9-month follow-up examination in all 21 patients. Fusion of the reconstructed laminae was found to be completed at 12 months in all 18 patients able to attend follow up for this duration. Spinal alignment and the range of motion of the cervical spine were well preserved. In patients with stenotic cervical myelopathy, neurological and anatomical outcome of canal expansion were satisfactory.

Conclusions. This technique enables rigid laminoplasty while maintaining anatomical and biomechanical integrity of posterior elements of cervical spine. Expansive and nonexpansive laminoplasty procedures are possible.

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Naohiro Tsuyuguchi, Ichiro Sunada, Yoshiyasu Iwai, Kazuhiro Yamanaka, Kiyoaki Tanaka, Toshihiro Takami, Yumiko Otsuka, Shinichi Sakamoto, Kenji Ohata, Takeo Goto and Mitsuhiro Hara

Object. In this study the authors examined how to differentiate radiation necrosis from recurrent metastatic brain tumor following stereotactic radiosurgery by using positron emission tomography (PET) with l-[methyl-11C]methionine (MET).

Methods. In 21 adult patients with suspected recurrent metastatic brain tumor or radiation injury, MET-PET scans were obtained. These patients had previously undergone stereotactic radiosurgery and subsequent contrast-enhanced magnetic resonance (MR) examinations before nuclear medicine imaging. Positron emission tomography images were obtained as a static scan of 10 minutes performed 20 minutes after injection of 370 MBq of MET. On MET-PET scans, the portion of the tumor with the highest accumulation of MET was selected as the region of interest (ROI), and the ratio of tumor tissue to normal tissue (T/N) was defined as the mean counts of radioisotope per pixel in the tumor divided by the mean counts per pixel in normal gray matter. The standardized uptake value (SUV) was calculated using the same ROI in the tumor. The accuracy of the MET-PET scan was evaluated by correlating findings with results of subsequent histological analysis (11 cases) or, in cases in which surgery or biopsy was not performed, with subsequent clinical course and MR imaging findings (10 cases).

Histological examinations performed in 11 cases showed viable tumor cells with necrosis in nine and necrosis with no viable tumor cells in two. Another 10 cases were characterized as radiation necrosis because the patients exhibited stable neurological symptoms with no sign of massive enlargement of the lesion on follow-up MR images after 5 months. The mean T/N was 1.15 in the radiation necrosis group (12 cases) and 1.62 in the tumor recurrence group (nine cases). The mean SUV was 1.78 in the necrosis group and 2.5 in the recurrence group. There were statistically significant differences between the recurrence and necrosis groups in T/N and SUV. Furthermore, the borderline T/N value was 1.42 according to a 2 × 2 factorial table (high T/N or low T/N, recurrence or necrosis). From this result, the sensitivity and specificity of MET-PET scanning in detecting tumor recurrence were determined to be 77.8 and 100%, respectively.

Conclusions. The use of MET-PET scanning is a sensitive and accurate technique for differentiating between metastatic brain tumor recurrence and radiation necrosis following stereotactic radiosurgery. This study reveals important information for creating strategies to treat postradiation reactions.