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Shiro Waga, Atsunori Morikawa and Tadashi Kojima

✓ A patient is reported with a purely pial arteriovenous malformation (AVM) supplied from the posterior parietal artery. The prominent middle meningeal artery contributed to opacification of the angular branches distal to the AVM, but did not contribute to the AVM. After total removal of the AVM, the angular branches became opacified from the middle cerebral artery. Review of the literature suggests that hypertrophied dural arteries which do not contribute to the AVM's but which do opacify the cortical branches distal to the AVM's are rare.

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Shiro Waga, Shinichi Shimosaka and Tadashi Kojima

✓ Nine cases with arteriovenous malformations (AVM's) predominantly involving the lateral ventricle are presented. All the AVM's were small, but caused intraventricular hemorrhage in eight cases. Only two patients had an intracerebral hemorrhage large enough to warrant evacuation. Eight patients were under the age of 40 years at the onset of their disease. Computerized tomography demonstrated intraventricular hemorrhage in eight patients, and after intravenous administration of contrast medium a small area of enhancement with dilated subependymal draining veins was seen in seven. The lateral ventricles were of normal size in seven cases, and only two patients required a shunting procedure. Angiography demonstrated that the lesion was an AVM in eight patients, and did not visualize the lesion in the ninth. One patient suffered a recurrent intraventricular hemorrhage when the AVM was demonstrated, although repeated angiography had failed to disclose a vascular lesion at his first intraventricular hemorrhage 14 months before.

All nine lesions were resected by microsurgical techniques, and the results were excellent in eight patients. Of four caudate lesions, three were resected through a frontal transcortical approach and the other was operated on through an anterior transcallosal approach; the results were excellent in three of these patients. Only one (Case 4) was left with neurological deficits; he had confusion and disorientation following a right frontal transcortical approach. Even in the dominant hemisphere, lesions in the head of the caudate nucleus could be safely resected by an anterior transcallosal approach. Two choroidal lesions located in the temporal horn and trigone on the dominant side were resected through a middle temporal gyrus approach, and three thalamic lesions through a posterior transcallosal approach, all with excellent results. In all cases the brain opening required was about the width of the retractor (maximum 2.0 cm, average 1.5 cm).

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Hiroshi Sakaida, Shiro Waga, Tadashi Kojima, Yoshichika Kubo, Shigehiko Niwa and Toshio Matsubara

✓ The authors report on the case of a 20-year-old man who presented with a transient tetraparesis. Neuroimaging studies demonstrated atlantoaxial dislocation and ventral compression of the rostral spinal cord caused by a quite rare association of os odontoideum and hypertrophic ossiculum terminale. The patient underwent removal of two free ossicula via a transoral approach and posterior fusion in which an autogenous bone graft was placed.

The majority of cases of os odontoideum are believed to be an acquired form; however, controversy with regard to the congenital causes of os odontoideum remains. One hypothesis is that os odontoideum results from the failure of fusion and the hypertrophy of the proatlas, although considerable confusion surrounds this hypothesis because definitive classification of os odontoideum—to differentiate between similar anomalies—has not been established. This rare coincidence in the current case supports the belief that os odontoideum has a different embryological origin from ossiculum terminale, which is thought to be a proatlantal remnant.

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Kazuhiro Ohtakara, Kenichi Murao, Kenji Kawaguchi, Yoshihiro Kuga, Tadashi Kojima, Waro Taki and Shiro Waga

✓ The authors describe the case of a 51-year-old man with a Type 1 dural arteriovenous fistula (AVF) located at the junction of the transverse and sigmoid sinuses. The dural AVF developed after the patient underwent a craniotomy for an acute extradural hematoma. The patient suffered pulsatile tinnitus 3 months after surgery. After several attempts at transarterial embolization (TAE), the venous channel located close to the skull fracture was accessed via a transfemoral—transvenous approach and was embolized by administering a liquid nonadhesive agent. Successful embolization of the dural AVF was achieved both clinically and radiologically without causing considerable hemodynamic alterations. This procedure, either alone or combined with TAE, would seem to be an alternative treatment for dural AVFs in this location, without causing compromise of flow within the affected sinuses, when selective venous access is available.

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Takeo Shimizu, Shiro Waga, Tadashi Kojima and Shigehiko Niwa

✓ A case of cerebellar infarction induced by repeated neck rotation (“bow-hunter's stroke”) is reported. The most likely mechanism is that repeated rotational neck movement brings about thickening of the atlanto-occipital membrane, fixing the vertebral artery in the vascular groove of the atlas. The vertebral artery is thus pinched at the time of neck rotation, leading to thrombus formation. Embolization results in cerebellar infarction. Surgical decompression of the vertebral artery at the level of the atlas in this case relieved the symptoms, and postoperative angiography demonstrated good flow within the vertebral artery even when the neck was rotated. It was not necessary to restrict the patient's neck movement postoperatively.

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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.