Search Results

You are looking at 1 - 10 of 24 items for

  • Author or Editor: Yoshikazu Okada x
Clear All Modify Search
Restricted access

Yasuo Aihara, Ichiro Shoji and Yoshikazu Okada

Object

The CSF shunt valve is a medical device whose main function is to regulate intracranial pressure and drain excess CSF. The authors have developed a new therapeutic method for treating hydrocephalus, namely the tandem shunt valve system, which has the potential of flexibly controlling the CSF flow rate and intracranial pressure in patients.

Methods

The properties of the tandem system were verified by performing in vitro experiments. An in vitro system with a manometer was built to measure pressure and flow rates of water in open systems using the Codman Hakim Programmable Valve and the Strata adjustable pressure programmable valve. A single valve and 2 single shunt valves connected in series (the tandem shunt valve system) were connected to the manometer to check the final pressure.

Results

Conventional single shunt valve systems require valve pressures to be set higher to slow down the CSF flow rate, which inevitably results in a higher final pressure. On the other hand, the tandem shunt valve system uses the combination of 2 valves to slow the CSF flow rate without increasing the final pressure.

Conclusions

The authors succeeded in experimentally demonstrating in vitro results of tandem systems and their effectiveness by applying a model to show that the valve with the higher pressure setting determined the final pressure of the entire system and the flow rate became slower than single shunt valve systems.

Restricted access

Yoshikazu Okada, Takeshi Shima, Noboru Yokoyama and Tohru Uozumi

✓ The authors produced occlusion of the middle cerebral artery (MCA) trunk in dogs by two methods: silicone cylinder embolization and trapping. Comparative analyses of the clinicopathological features in these models, extending from the acute to chronic stage, were performed.

Within 24 hours after embolization, the brain exhibited swelling without macroscopic infarction. Microangiograms revealed impaired filling in the deep areas of the brain with midline shift. At 4 to 7 days after embolization, the animals showed major neurological deficits, evident deep cerebral infarction, and poorly perfused areas in the deep cerebrum with prominent midline shift. At 3 to 4 weeks after embolization, the neurological deficits improved and the affected regions showed cavities or localized lesions. Microangiograms demonstrated hypervascular areas with abnormal vessels in the affected cerebrum. On the other hand, trapping of the MCA trunk produced mild neurological deficits, although there was no evidence of macroscopic lesions or impairment of filling. This study shows that silicone cylinder embolization in the MCA trunk produces a reliable and reproducible deep cerebral infarction in dogs.

Restricted access

Yoshikazu Okada, Takeshi Shima, Shuichi Oki and Tohru Uozumi

✓ The effects of microsurgical embolectomy were investigated clinicopathophysiologically in 60 dogs after occlusion of the middle cerebral artery (MCA) trunk with a silicone cylinder embolus. One group of animals served as a control (non-embolectomized group), and in the other two groups the embolus was removed 3 or 6 hours after occlusion (3-hour or 6-hour embolectomy group). In the non-embolectomized animals, major neurological deficits with deep cerebral infarction were observed. Regional cerebral blood flow (CBF) in the basal ganglia decreased most prominently. Sensory evoked potentials also declined to about 50% of the control level 3 hours after embolization. In the 3-hour embolectomy group, mild neurological deficits with minimal infarctions were found. One hour after embolectomy, CBF was restored to the original level in all regions, and the sensory evoked potentials surpassed the control level. In the 6-hour embolectomy group, most animals exhibited major neurological deficits and severe brain swelling with hemorrhagic infarction. This study suggests that early microsurgical embolectomy of the MCA trunk restores blood flow in the perforating arteries and prevents deep cerebral infarction.

Restricted access

Yoshikazu Okada, Takeshi Shima, Masahiro Nishida and Kanji Yamane

✓ The authors describe the application of a Dacron tube as a retroauricular subcutaneous tunnel in extracranial-intracranial autologous vein bypass graft.

Restricted access

Yoshikazu Okada, Takeshi Shima, Mitsuo Yamamoto and Tohru Uozumi

✓ Regional cerebral blood flow (rCBF), sensory evoked potentials (SEP), and intracranial pressure (ICP) were investigated in dogs with focal cerebral ischemia produced by a silicone cylinder embolus in the middle cerebral artery (MCA) trunk as compared to that produced by trapping the same vessel. These variables were measured at intervals of 1 hour for a period of 6 hours after MCA occlusion.

In the embolized animals, rCBF decreased most extensively at the basal ganglia, from a control level of 53.9 ± 3.9 (mean ± SE) to 21.5 ± 2.7 ml/100 gm/min at the 6th hour. Sensory evoked potentials decreased progressively from the resting level of 100% to 53.0% ± 7.2% at the 3rd hour. Intracranial pressure, measured by epidural pressure on the occluded side, increased rapidly during the first 3 hours, from 10.6 ± 0.3 to about 30 cm H2O.

In the animals with trapping, the decreases in rCBF and declines of SEP were significantly less than those in the embolized animals, and no evident brain swelling was observed. This study demonstrates that MCA trunk occlusion by silicone cylinder embolization produces a more marked decrease in deep CBF, with diminution of SEP and increase in ICP, than that produced by trapping.

Restricted access

Yoshikazu Okada, Otmar Kloiber and Konstantin A. Hossmann

✓ Experimental brain tumors were produced in cats by xenotransplantation of the rat glioma clone F98 into the white matter of the left hemisphere. One to 4 weeks after implantation, local adenosine triphosphate (ATP), glucose, lactate, and tissue pH were measured via imaging techniques in cryostat sections passing through the center of the tumor and correlated with changes in water and electrolyte content. The tumors exhibited a heterogeneous metabolic pattern, with a tendency for ATP to decrease and lactate to increase during tumor development. Tissue pH was above 7.5 in tumors with high ATP content but it sharply declined at low ATP levels. In peritumoral edema, ATP also decreased and lactate increased but, in contrast to tumor tissue, pH became more alkaline. Metabolic changes were associated with edema formation, as evidenced by the rise in water and sodium content. There was a distinct difference between tumor tissue and peritumoral edema: in tumor tissue, pH declined with increasing water content, whereas in peritumoral edema it increased.

These observations are interpreted as follows: 1) in tumor tissue, “lactacidosis” and ATP depletion are attributed to disturbances in blood flow, resulting in metabolic failure and the intracellular “cytotoxic” accumulation of water; 2) in peritumoral edema, “lactalkalosis” is the result of an efflux of (alkaline) lactate salts from the tumor into the expanded extracellular compartment, and the decrease in ATP is the volumetric effect of extracellular “vasogenic” edema fluid and not the result of cellular energy failure. These findings are of importance for the interpretation of volume-selective magnetic resonance spectroscopy and may contribute to the establishment of spectroscopic criteria for the evaluation of therapeutical interventions.

Restricted access

Tetsuji Inagawa, Masaaki Shibukawa, Futoshi Inokuchi, Yoshio Tokuda, Yoshikazu Okada and Kazunori Okada

Object. The purpose of this study was to assess the overall management and surgical outcome of primary intracerebral hemorrhage (ICH) and aneurysmal subarachnoid hemorrhage (SAH) among the 85,000 residents of Izumo City, Japan.

Methods. During 1991 through 1996, 267 patients with ICH and 123 with SAH were treated in Izumo. Of the 267 patients with ICH, 25 underwent hematoma removal by open craniotomy or suboccipital craniectomy and 34 underwent stereotactic evacuation of the hematoma, whereas aneurysm clipping was performed in 71 of the 123 patients with SAH; operability rates were thus 22% for ICH and 58% for SAH (p < 0.0001). The overall 30-day survival rates were 86% for ICH and 66% for SAH (p < 0.0001) and the 2-year survival rates were 73% and 62% (p = 0.0207), respectively. In patients who underwent surgery, 30-day and 2-year survival rates were 93% for ICH and 100% for SAH (p = 0.0262), and 75% for ICH and 97% for SAH (p = 0.0002), respectively. In patients with ICH, the most important predictors of 30-day case-fatality rates were the volume of the hematoma, the Glasgow Coma Scale (GCS) score, rebleeding, and midline shifting, whereas those for 2-year survival were the GCS score, age, rebleeding, and hematoma volume. In patients with SAH, the most important determinants of 30-day case-fatality rates were the GCS score and age, whereas only the GCS score had a significant impact on 2-year survival.

Conclusions. The overall survival rates for patients with ICH or SAH in Izumo were more favorable than those in previously published epidemiological studies. However, despite improved surgical results, the overall management of ICH and SAH still produced an unsatisfactory outcome, mainly because of primary brain damage.

Full access

Taku Yoneyama, Takakazu Kawamata, Masahiko Tanaka, Koji Yamaguchi and Yoshikazu Okada

In carotid endarterectomy (CEA), the traditional retractors are often difficult to use because they tend to obstruct surgical manipulations, especially in the deep operative field on the rostral side. The authors have invented a new omnidirectional retractor-supporting ring (OD ring) to solve the problems of traditional retractors. The OD ring has an ellipsoid-shaped frame (major axis: 275 mm, minor axis: 192 mm) with 22 equally spaced outward protrusions. Rubber bands from which blunt mini-hooks are hung are twisted around the protrusions. The OD ring was placed on the operative area, and the skin edges were retracted by mini-hooks placed symmetrically. The hooks were moved gradually from the shallow to the deep operative field as surgical dissection continued to expose the carotid bifurcation and distal internal carotid artery (ICA). The OD ring was used in 158 consecutive CEAs in the authors' institute between July 2010 and October 2013. The OD ring provided a flatter surgical field and was less obstructive than traditional retractors, thereby facilitating surgical manipulation in the deep operative field such as at the distal ICA. Furthermore, because of its simpler shape, angiorrhaphy could be conducted more smoothly, with less tangled thread during closure of the arteriotomy. There were no technical complications related to the OD ring. As a new retractor system for CEA, the OD ring is less obstructive and provides a flatter surgical field than traditional retractors, thereby facilitating surgical manipulations in the deep operative field around the distal ICA.

Restricted access

Seiichiro Eguchi, Yasuo Aihara, Kohji Yamaguchi and Yoshikazu Okada

A fetus at 30 gestational weeks was observed on fetal ultrasonography to have a dilated right lateral ventricle. After delivery, the entity was diagnosed as a prenatal intracerebral hemorrhage (ICH) due to a ruptured arteriovenous malformation (AVM). Ultrasonography and MRI examinations performed before birth indicated a cerebral aneurysm in the territory of the right middle cerebral artery. However, digital subtraction angiography revealed an intracystic hemorrhage due to a ruptured cerebral AVM.

Arteriovenous malformations in children are rare, difficult to diagnose, and result in permanent sequelae after delayed treatment. Patient prognosis depends on early and accurate diagnosis and intervention. Outcomes can be improved if an AVM in a child is detected at the onset of ICH for young infants in the prenatal or early postnatal periods. Early AVM diagnosis is limited to fetal ultrasonography and MRI, and special consideration through invasive examination including neonatal digital subtraction angiography is urged unless a correct and clear diagnosis is made at an early stage. Prenatal ICH due to an AVM is rare. The authors discuss their observations and findings.

Free access

Hideo Okada, Yoshikazu Matsuda, Joonho Chung, R. Webster Crowley and Demetrius K. Lopes