PubMed Health⌕ Search

Biomedical subjects

Namio Kodama

Publications and source records attributed to Namio Kodama.

At least 19 recordsLinked to original sources
PubMed2007

High-frequency monopolar electrical stimulation of the rat cerebral cortex.

OBJECTIVE: Intraoperative monitoring of the motor-evoked potential has been widely used in patients undergoing neurosurgery. Direct stimulation of the brain with high-frequency monopolar stimulation (HFMS) is one of the most common methods to produce motor-evoked potential. We studied the influence of HFMS on the rat cerebral cortex. METHODS: We applied 1.5, 15, 30, 40, or 50 mA of HFMS to the rat sensorimotor cortex by a short sequence of five monopolar, monophasic, anodal rectangular 500-Hz pulses. We delivered one short five-pulse train 100 times every 5 seconds and examined pre- and post-stimulation electroencephalograms and histological changes at the stimulation site. RESULTS: We observed no spike waves after HFMS in any of the rats. There was no change in the power spectrum or frequency content in any of the rats exposed to HFMS. Histologically, there was significant swelling of the dendrites in rats sacrificed immediately after exposure to 40- and 50-mA stimulation; the 50-mA stimulation group also exhibited slight swelling of the mitochondria. These findings were not obtained in any of the rats sacrificed 30 days after stimulation. CONCLUSION: In rats exposed to a stimulation intensity of 30-mA or less, no morphological or electrophysiological changes were observed. However, the possibility that HFMS may affect neural tissue cannot be ruled out.

Action Potentials↗
PubMed2006

[Intraoperative monitoring of visual evoked potentials].

Our success rate of intraoperative monitoring of visual evoked potential (VEP) had been approximately 30% in the past. In order to improve recording rate of intraoperative VEP, we developed a new stimulating device using high power light emitting diodes. Electroretinogram was simultaneously recorded to understand whether flash stimulation reached the retina. In addition, total venous anesthesia with propofol was used to avoid the adverse effect of inhalation anesthesia. We report the results after introduction of these improvements. Intraoperative monitoring of VEP was attempted in 35 cases. We evaluated success rate of VEP recording, correlation between VEP findings and postoperative visual function, and reasons why recording was not successful. Stable and reproducible waveforms were obtained in 59 sides (84%). Two cases, whose VEP deteriorated intraoperatively, developed postoperative visual disturbance: In 11 sides (16%), stable waveforms were not obtained. There were two main causes. In 8 sides out of 11, the cause was attributed to pre-existing severe visual disturbance. In these 8 sides, VEP in the awake state was not recordable or was recordable, but with very low amplitudes under 1 microV. In the other 3 sides, the cause was attributed to movement of a stimulating device by reflecting the fronto-temporal scalp flap. In conclusion, the successful recording rate was increased to 84% from approximately 30%, after introduction of various trials. We need further improvement in recording intraoperative VEP to establish a reliable intraoperative monitoring method for VEP.

Aged↗
PubMed2005

Melanotic neuroectodermal tumor of infancy in the skull: case report and review of the literature.

BACKGROUND: Melanotic neuroectodermal tumor of infancy (MNTI) is a rare neoplasm that develops during the first year of life and grows rapidly. Early diagnosis and radical surgery are critical for a long-term cure. We report a rare case of MNTI in the skull and discuss the importance of the radical surgery and the long-term follow-up results. CASE PRESENTATION: We describe a case of a 4-month-old girl with an MNTI in the skull who underwent the operation 11 years ago. The mass in the frontotemporosphenoid region grew rapidly after birth. The patient underwent a craniotomy. By referring to the histological findings of frozen section during surgery, a total excision of the tumor including its adjacent hypertrophic bone was performed. The patient has remained well without evidence of recurrence or neurological abnormality for 11 years. CONCLUSION: Radical surgery for MNTI provides complete cure. According to the literature including our case, there should be follow-up for at least 2 years after surgery. Especially in cases in which tumors recur, follow-up should be for longer periods because of the possibility of its malignant change.

Child↗
PubMed2005

Experimental model of intracranial arteriovenous shunting in the acute stage.

A model of intracranial arteriovenous (AV) shunting must incorporate local hypoperfusion and simulate the hemodynamics of arteriovenous malformations. In this study, the hemodynamics of an intracranial AV shunt model in the acute stage were clarified. End-to-side anastomoses with a femoral vein graft were performed between a cortical branch of the middle cerebral artery (MCA) and the superior sagittal sinus in anesthetized dogs. Local cerebral blood flow (l-CBF) was measured by laser Doppler blood flowmetry. l-CBF decreased suddenly by 34.2% when the shunt was opened in the ipsilateral MCA territory. Upon re-occlusion, l-CBF immediately equaled or exceeded the pre-opening value and returned to the pre-opening value within the next 15 minutes. Opening the shunt produced little change in l-CBF in the territory of the ipsilateral or contralateral anterior cerebral artery. The decrease in l-CBF was correlated with shunt volume only in the MCA territory. l-CBF manifested a PaCO(2)-dependent increase before shunt opening, but CO(2) reactivity was impaired after opening the shunt only in the MCA territory. This dog model features local hypoperfusion due to intracranial AV shunting and disturbance of CO(2) reactivity in the acute stage. The hemodynamics of this model will be confirmed in the chronic stage.

Animals↗
PubMed2005

Optic nerve evoked potentials elicited by electrical stimulation.

This study investigated whether the optic nerve evoked potential (ONEP) elicited by electrical stimulation of the optic nerve can serve as a reliable intraoperative indicator of visual function. In the experimental study, two silver-ball stimulating electrodes were placed on the dog optic nerve adjacent to the apex of the orbit and one recording electrode was placed on the optic nerve near the chiasm. The nerve was stimulated with 0.1 to 10 mA rectangular pulses. Stable and reproducible ONEPs were obtained. The ONEPs were not influenced by electromyographic potentials and were recorded more clearly on the optic nerve than on the surrounding tissue. Stepwise incremental transection of the thickness of the nerve resulted in incremental amplitude reduction proportional to the transected area. No response was recorded after complete sectioning of the nerve. In the clinical study, recordings were obtained from 15 patients after craniotomy to treat parasellar tumors or cerebral aneurysms. Reproducible ONEPs were recorded intraoperatively from the electrode placed on the optic nerve near the chiasm in 14 of 15 patients. In the remaining patient, the ONEP, recorded only after tumor removal because the optic nerve was stretched and extremely thin, was remarkably small and the patient developed unilateral blindness postoperatively. These experimental and clinical results suggest the possibility of intraoperative monitoring of visual function in patients undergoing craniotomy for the treatment of lesions near the optic nerve.

Adult↗
PubMed2005

Medico-legal aspects of traumatic injury of the vertebrobasilar artery.

Based on our experiences with medico-legal autopsies, we analyzed traumatic injury of the vertebrobasilar artery (VBA) in traffic accident victims. VBA rupture occurred in six cases with traumatic medullary lesions, but in none with cervical cord injury. A relatively small external force applied to the head or neck can induce isolated traumatic subarachnoid hemorrhage (SAH), which accounts for approximately 11% of fatal head injuries. We examined the relationship between site of impact and site of vascular injury in 16 cases of isolated traumatic SAH. The results showed that the vertebral artery (VA) on the side of impact tended to be longitudinally injured in victims experiencing an external force equivalent to that of a fist punch to the head or face. There was no clear relationship between the site of impact and the site of vascular injury in victims who had sustained an external force greater than that of a fist punch. However, our results suggest that an external force causing rotation of the head was likely to cause tearing of the artery. In cases in which an external force equivalent to that of a fist punch was applied to the head, a raised blood alcohol level was a significant risk factor for artery rupture. Furthermore, a difference in the diameters of the left and right VAs was a risk factor for artery rupture. To determine why the VA, the most frequent site of arterial dissection, is also frequently the site of injury, we histologically examined normal and dissected VBAs. We also discuss medico-legal issues of the causal relationship between external force applied and rupture or dissection of the VA.

Basilar Artery↗
PubMed2005

Effects of N-methyl-d-aspartate, glutamate, and glycine on the dorsal column axons of neonatal rat spinal cord: in vitro study.

The effects of N-methyl-D-aspartate (NMDA), glutamate, and glycine on the developmental axons of the neonatal rat spinal cord were investigated. Isolated dorsal column preparations from postnatal day (PN) 0 to 14 Long-Evans hooded rats (n = 119) were used in vitro. Compound action potentials (CAPs) were recorded from the cuneate and gracile fasciculi with a glass micropipette electrode. NMDA (100 microM) significantly increased CAP amplitude in PN 0-6 cords by 21.5 +/- 9.2% (mean +/- standard error of the mean, p < 0.001, n = 8) and in PN 7-14 cords by 6.7 +/- 6.6% (p < 0.001, n = 10). NMDA (10 microM) significantly increased the CAP amplitude by 6.3 +/- 2.9% in PN 0-6 cords (p < 0.01, n = 10). The increase of CAP amplitude induced by NMDA (100 microM) in PN 0-6 cords was significantly greater than that in PN 7-14 cords (p < 0.005). Glutamate (100 microM) significantly increased the CAP amplitude by 8.8 +/- 8.1% in PN 0-6 cords (p < 0.001, n = 29) and 6.7 +/- 7.5% in PN 7-14 cords (p < 0.01, n = 14), and glutamate (10 microM) significantly increased by 6.3 +/- 2.9% in PN 0-6 cords (p < 0.01, n = 21). The amplitudes induced by glutamate (100 microM or 10 microM) did not significantly differ between PN 0-6 and PN 7-14 cords. Application of glycine (100 microM) did not significantly alter CAP amplitudes induced by NMDA (100 microM or 10 microM) and glutamate (100 microM or 10 microM). D(-)-2-amino-5-phosphonopentanoic acid (NMDA receptor antagonist) blocked the effects of NMDA and glutamate. These results suggest that NMDA receptor is present on afferent dorsal column axons and may modulate axonal excitability, especially during the 1st week after birth.

Age Factors↗
PubMed2005

Intraoperative monitoring of blood flow insufficiency during surgery of middle cerebral artery aneurysms.

OBJECT: The usefulness of motor evoked potential (MEP) monitoring to detect blood flow insufficiency (BFI) in the cortical branches of the middle cerebral artery (MCA) and lenticulostriate arteries (LSAs) during MCA aneurysm surgery was investigated based on the correlation between MEP and somatosensory evoked potential (SEP) monitoring. METHODS: Fifty-three patients with MCA aneurysms underwent surgery accompanied by intraoperative MEP and SEP monitoring. There was no postoperative motor paresis in 43 patients in whom MEP and SEP results remained unchanged. In the other 10 patients, nine manifested transient MEP changes; in five of these, SEP changes did not occur. The transient MEP changes were thought to be attributable to BFI of the MCA cortical branches in two patients, the LSA in three, and either the MCA branches or the LSA in four patients. Of these nine patients, six did not present with postoperative motor paresis; transient motor paresis was recognized in the other three. In the 10th patient, MEP waves disappeared and did not recover. This patient's SEPs remained at 70% of the control level, and he developed severe hemiparesis. A postoperative computerized tomography scan revealed a new low-density area in the corona radiata and putamen. CONCLUSIONS: Blood flow insufficiency in both the LSA and MCA cortical branches that perfuse the corticospinal tract can be detected by intraoperative MEP monitoring. Somatosensory evoked potential monitoring is not reliable enough to detect BFI in the MCA branches and the LSAs.

Aged↗
PubMed2005

3D-CT arteriography and 3D-CT venography: the separate demonstration of arterial-phase and venous-phase on 3D-CT angiography in a single procedure.

Although 3D-CT angiography provides valuable anatomic information regarding lesion and their surrounding vessels and bony structures, it cannot demonstrate lesions, arteries, and veins, separately. The separate demonstration of arterial-phase 3D-CT angiography (3D-CT arteriography) and venous-phase 3D-CT angiography (3D-CT venography) will facilitate the understanding of the vascular anatomy within lesions, thus, allowing improvement of diagnostic accuracy and potentially a safer surgical approach. We describe 3D-CT arteriography and 3D-CT venography by using a multidetector row helical CT.

Adult↗
PubMed2004

Management of poor-grade patients with aneurysmal subarachnoid hemorrhage in the acute stage: Importance of close monitoring for neurological grade changes.

BACKGROUND: The optimal management of poor-grade patients with aneurysmal subarachnoid hemorrhage (SAH) remains controversial. We evaluated therapeutic outcomes to identify appropriate treatments for SAH patients admitted with a poor grade. METHODS: We retrospectively studied 136 patients admitted within 6 hours after SAH onset with a poor Hunt & Kosnik Grade (IV and V). RESULTS: Of 136 poor-grade patients, 20 with massive intracerebral or subdural hematoma underwent urgent hematoma evacuation and aneurysmal neck clipping. Seven of these achieved a favorable outcome (good recovery or moderate disability). Another 7 patients with prominent hydrocephalus or massive intraventricular hematoma underwent urgent continuous ventricular drainage. Of these, 4 manifested spontaneous grade improvement and underwent neck clipping; the other 3 died resulting from rebleeding. The remaining 109 patients whose poor grade was primarily because of SAH were observed without immediate surgery. In 43 patients of 109, the grade improved within 24 hours after hospitalization and within 38 hours in the other 4 patients. Aneurysmal neck clipping was performed in these 47 patients and a favorable outcome was achieved in 25 patients. The remaining 62 patients did not improve and the outcome was unfavorable. CONCLUSIONS: Poor-grade SAH patients should be treated according to the pathogenesis underlying their poor grade. Close monitoring for a grade change over the first 24 hours after hospitalization is mandatory in patients whose poor grade is primarily because of the SAH and helps to determine the appropriateness of surgery.

Adult↗
PubMed2004

Perinidal dilated capillary networks in cerebral arteriovenous malformations.

OBJECTIVE: The perinidal vascular structures of cerebral arteriovenous malformations were examined, to clarify their pathomorphological features. METHODS: Twenty-two resected specimens of human brain structures adjacent to the nidus were examined. The vessels surrounding the nidus were three-dimensionally reconstructed with a computer graphics system. RESULTS: In all cases, the analysis of serial sections revealed that perinidal dilated capillaries were located in brain tissue 1 to 7 mm from the nidal border. The vessels surrounding the nidus demonstrated markedly dilated capillary networks (perinidal dilated capillary network [PDCN]). The diameters of the vessels forming the PDCN were 10 to 25 times those of normal capillaries. The PDCN connected not only to the nidus, feeding arteries, and draining veins, via arterioles and venules, but also to the normal capillary network, arterioles, and venules. CONCLUSION: Without exception, each nidus was accompanied by a PDCN, which connected not only to the nidus, feeding arteries, and draining veins, via arterioles and venules, but also to normal capillaries, arterioles, and venules. The PDCN should be considered in studies aimed at gaining an understanding of the mechanisms underlying the intraoperative and postoperative bleeding, growth, and recurrence of surgically treated cerebral arteriovenous malformations.

Adolescent↗
PubMed2004

Thalamic arteriovenous malformation with an unusual draining system--case report.

A 52-year-old man suddenly experienced headache and vomiting. Computed tomography demonstrated a small area of hemorrhage in the right cerebellar hemisphere. Angiography revealed a thalamic arteriovenous malformation (AVM) fed by the bilateral medial posterior choroidal arteries and left marginal tentorial artery, and drained into the confluence via the cerebellar veins without flow into the supratentorial venous system. The draining veins included two varices, one of which, in the right cerebellar hemisphere, was thought to be the source of bleeding. The AVM nidus was removed via the right occipital transtentorial approach. A portion of a drainer adhered to the surface of the great vein of Galen but without opening into the galenic system and all drainers from this thalamic AVM flowed into the infratentorial cerebellar venous system.

Cerebral Angiography↗
PubMed2004

Histological study of the normal vertebral artery--etiology of dissecting aneurysms.

Histological evaluation of dissecting aneurysms of the cerebral arteries has suggested that defects in the internal elastic lamina (IEL) induce dissection of the arterial wall. Dissecting aneurysms occur most frequently in the vertebral artery (VA). The present study examined sections of the normal VA to elucidate the mechanisms of arterial dissection. Bilateral VAs (20 vessels) were obtained from 10 patients who died of causes other than intracranial lesions. The VAs were detached from the VA union to the site 10 mm proximal from the point penetrating the dura mater. The VAs were cut at 5-mm intervals, and each segment was observed using modified Masson's trichrome staining for elastic fibers. The thickness of the media and adventitia significantly thinned after the origin of the posterior inferior cerebellar artery (PICA). IEL defects were observed at 35 sites in 11 vessels from six subjects. There was a high incidence of IEL defects in the extradural portion and near the origin of the PICA, areas frequently involved in arterial dissection. There was a high incidence of intimal thinning at areas of IEL defects (19 of 35), and thinning was particularly marked distal to the origin of the PICA. In the absence of intimal thickening, the vascular strength at the site of IEL defects may be reduced, which would promote the occurrence and progression of arterial dissection.

Adult↗
PubMed2004

Monitoring and preventing blood flow insufficiency due to clip rotation after the treatment of internal carotid artery aneurysms.

The authors report a case in which anterior choroidal artery (AChA) blood flow insufficiency due to aneurysm clip rotation was detected intraoperatively by motor evoked potential (MEP) monitoring and ischemia was successfully avoided. The patient had an incidentally discovered aneurysm for which occlusion of its neck was performed through a standard frontotemporal craniotomy without changing the MEP amplitude. After it was confirmed that the surrounding arteries were not stenotic, the brain retractor on the frontal lobe was released; MEP amplitude subsequently decreased. Rotation of the clip toward the frontal base by repositioning of the frontal lobe caused the AChA stenosis at the origin of its branches. On reorienting the clip toward the frontal lobe, the AChA stenosis was released and MEP amplitude recovered. To prevent repeated clip rotation, a large amount of gelatin (Spongel) was inserted between the frontal base and the clip. The authors confirmed that clip rotation did not occur after repositioning of the frontal lobe. Motor evoked potential amplitude was maintained until dural closure. Postoperatively, the patient demonstrated no neurological deficit and there was no newly developed low-density area on computerized tomography scans.

Adult↗