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Biomedical subjects

T Shibazaki

Publications and source records attributed to T Shibazaki.

At least 19 recordsLinked to original sources
PubMed2001

Stress analysis in the TMJ during jaw opening by use of a three-dimensional finite element model based on magnetic resonance images.

This study was designed to investigate temporomandibular joint (TMJ) stress distribution during mouth opening using a finite element (FE) model of an individual TMJ based on magnetic resonance (MR) images. A dry skull with a silicon disk was used to test the three-dimensional reconstruction procedure, and showed enough accuracy and reproducibility in linear dimensions and disk volume for the following FE modelling for stress analysis in the TMJ. From an individual FE analysis of a normal subject, relatively high stresses were observed in the anterior and posterior regions of the disk during mouth opening, and furthermore, the superior boundary contacting with the glenoid fossa exhibited lower stresses than those on the inferior boundary facing the condyle. During transmission of stress through the disk, mechanical stress may be reduced by the stress redistribution function of the disk.

Adult↗
PubMed2001

Lesioning the thalamus for dyskinesia.

Recent advances on understanding the pallidothalamic relation lead us to perform Vim-Vo thalamotomy (combined thalamic lesion in ventralis intermedius nucleus and ventralis oralis nucleus) for cases with dyskinesia. In our recent series of thalamotomies, there are 12 cases of dyskinesia caused by various etiologies. Therefore the clinical manifestation of the involuntary movement was different in each case, including, more or less, some elements of irregular involuntary hyperkinetic movement. Stereotactic operation was performed using Leksell's apparatus aided by Surgiplan and MRI. The Vim nucleus was identified by physiological study using microelectrodes. High background activity and kinesthetic neurons are reliable indicators of Vim nucleus (but only for the lateral part). Then, selective coagulation was made by dual coagulation needles. Since the Vo nucleus is located just rostral to the Vim nucleus, the coagulation needle was turned toward the anterior part to partly cover the Vo nucleus. Thus, selective Vim-Vo thalamotomy was shown to be quite successful for the treatment of dyskinesia.

Antiparkinson Agents↗
PubMed2000

Parenchymal perianeurysmal cystic changes in the brain: report of five cases.

PURPOSE: To describe parenchymal perianeurysmal cystic changes in the brain. MATERIALS AND METHODS: Among 247 patients with cerebral aneurysms described in the medical or radiologic records in three institutions, five had perianeurysmal cystic changes. These were evaluated with computed tomography or magnetic resonance (MR) imaging and were categorized according to size, appearance, and the presence of hemosiderin deposit. Confirmation at stereotactic needle biopsy was available in one case. RESULTS: Perianeurysmal cysts comprised multiple clustered cysts in three cases and a unilocular cyst in two, and diameters were 1.5-3.5 cm. Hemosiderin was depicted at MR imaging in one unilocular cyst. Associated aneurysms had diameters of 0.7-4.0 cm, and prominent aneurysmal thrombosis and calcifications were seen in two cases. Findings at stereotactic needle biopsy were of mild reactive gliosis. At long-term follow-up in two patients, the cystic regions were stable. CONCLUSION: Parenchymal perianeurysmal cysts are rare and may display various morphologic characteristics from unilocular to multilocular. Since there may or may not be evidence of previous hemorrhage, other mechanisms such as abnormal angiogenesis factors may play a role.

Adult↗
PubMed2000

Gamma knife radiosurgery as a primary treatment for prolactinomas.

OBJECT: The purpose of this study was to estimate the efficacy of gamma knife radiosurgery (GKS) in controlling tumor growth and endocrinopathy associated with prolactinomas. METHODS: Between 1993 and 1997, 164 of 469 patients with pituitary adenomas treated by GKS harbored prolactinomas. The dose to the tumor margin ranged from 9 to 35 Gy (mean 31.2 Gy), and the visual pathways were exposed to a dose of less than 10 Gy. The mean tumor diameter was 13.4 mm. The mean follow-up time for 128 cases was 33.2 months (range 6-72 months). Tumor control was observed in all but two patients who underwent surgery 18 and 36 months, respectively, after GKS. Clinical cure was achieved in 67 cases. Clinical improvement was noted with a decrease in the hyperprolactinemia after GKS. Nonetheless, in 31 (29%) of 108 patients who were followed for more than 2 years no improvement in serum prolactin levels was demonstrated, although this could be normalized by bromocriptine administration after treatment. Nine infertile women became pregnant 2 to 13 months after GKS and all gave birth to normal children. There was no visual deterioration related to GKS. Five women experienced premature menopause. In these patients there was subtotal disappearance of the tumor and an empty sella developed. CONCLUSIONS: Gamma knife radiosurgery as a primary treatment for prolactinomas can be safe and effective both for controlling tumor growth and for normalization of prolactin hypersecretion. A higher margin dose (> or = 30 Gy) seemed to be associated with a better clinical outcome. Gamma knife radiosurgery may make prolactinomas more sensitive to the bromocriptine.

Humans↗
PubMed1999

Pituitary adenomas treated by microsurgery with or without Gamma Knife surgery: experience in 122 cases.

The clinical outcome of 122 patients with pituitary adenomas treated by microsurgery and/or Gamma Knife radiosurgery (GKRS) was analyzed to evaluate patient selection criteria and the role of GKRS. Sixty-six resections were performed in 59 patients. All tumors were macroadenomas, except for 5 ACTH-producing adenomas. Twenty-four of the 31 hypersecreting adenomas showed normal serum hormone values after treatment. Postoperative complications were rhinorrhea, cranial nerve palsies, and a small thalamic infarct. GKRS was performed on 18 of the operated patients because of residual tumors, mostly in the cavernous sinus. Thirty-five of the 63 patients treated by GKRS were followed for more than 2 years. All adenomas except 2 were stable or had decreased in size. Eleven of 17 functioning adenomas showed normal serum hormone values after treatment. It is concluded that tumors that compress the optic pathway should be removed and that residual tumors in the cavernous sinus are good indications for radiosurgery.

Adenoma↗
PubMed1997

Acute lymphoblastic leukemia with isolated adrenocorticotropic hormone deficiency.

A 57-year-old female was admitted to our hospital because of Philadelphia chromosome (Ph)-positive acute lymphoblastic leukemia (ALL). On admission, disturbance of consciousness and hyponatremia were recognized. The patient's endocrinological data showed low levels of adrenocorticotropic hormone (ACTH) (less than 5 pg/ml) and cortisol (5.9 microg/dl). Other anterior pituitary hormones were normal. Plasma ACTH and cortisol did not respond to the corticotropin releasing factor (CRF) test. A diagnosis of isolated ACTH deficiency was made. This is a rare case of isolated ACTH deficiency complicated with hematological malignancies.

Adrenocorticotropic Hormone↗
PubMed1996

Gamma knife for glioma: selection factors and survival.

PURPOSE: To determine factors associated with survival differences in patients treated with radiosurgery for glioma. METHODS AND MATERIALS: We analyzed 189 patients treated with Gamma Knife radiosurgery for primary or recurrent glioma World Health Organization (WHO) Grades 1-4. RESULTS CONCLUSION: The median minimum tumor dose was 16 Gy (8-30 Gy) and the median tumor volume was 5.9 cc (1.3-52 cc). Brachytherapy selection criteria were satisfied in 65% of patients. Median follow-up of all surviving patients was 65 weeks after radiosurgery. For primary glioblastoma patients, median survival from the date of pathologic diagnosis was 86 weeks if brachytherapy criteria were satisfied and 40 weeks if they were not (p = 0.01), indicating that selection factors strongly influence survival. Multivariate analysis showed that increased survival was associated with five variables: lower pathologic grade, younger age, increased Karnofsky performance status (KPS), smaller tumor volume, and unifocal tumor. Survival was not found to be significantly related to radiosurgical technical parameters (dose, number of isocenters, prescription isodose percent, inhomogeneity) or extent of preradiosurgery surgery. We developed a hazard ratio model that is independent of the technical details of radiosurgery and applied it to reported radiosurgery and brachytherapy series, demonstrating a significant correlation between survival and hazard ratio. CONCLUSIONS: Survival after radiosurgery for glioma is strongly related to five selection variables. Much of the variation in survival reported in previous series can be attributed to differences in distributions of these variables. These variables should be considered in selecting patients for radiosurgery and in the design of future studies.

Adolescent↗
PubMed1996

Relevance of the arginine transport activity to the nitric oxide synthesis in mouse peritoneal macrophages stimulated with bacterial lipopolysaccharide.

Transport of arginine and production of nitrite have been investigated in mouse peritoneal macrophages stimulated with bacterial lipopolysaccharide (LPS). The arginine transport activity was induced by LPS at very low concentration (maximally induced at 1 ng/ml), whereas much higher concentration of LPS was required for the induction of nitrite production. Arginine was more concentrated in the cells when its transport activity was induced. Lysine, which is a competitive inhibitor of the transport of arginine, neutralized the concentrative effect of the induced transport activity and thus inhibited the nitrite production. Induction of the arginine transport activity seems to be prerequisite to the enhanced synthesis of nitric oxide in activated macrophages.

Amino Acid Transport Systems↗
PubMed1996

Radiobiological effects of gamma knife radiosurgery on brain tumors studied in autopsy and surgical specimens.

To elucidate the radiobiological effect of Gamma Knife radiosurgery on brain tumors, we performed a histological study on nine cases. In two, the material was obtained at autopsy and in seven following surgery. In the central region of the radiation field, destructive changes occurred both in tumor cells and in vessels. In the peripheral area, destructive and proliferative vascular changes were intermingled with residual tumor tissue. Immunohistochemical staining of surgical specimens showed that the vascular proliferative changes consisted of pericytic proliferation with or without endothelial proliferation. These characteristic changes might suppress tumor growth, at least in the short-term.

Adolescent↗
PubMed1996

Gamma thalamotomy for parkinsonian and other kinds of tremor.

On the basis of our experiences with selective ventralis intermedius thalamotomy with microrecording, certain cases of tremor with Parkinson's disease (PD, six cases), intentional tremor (one case) and essential tremor (one case) were treated by Gamma Knife. In all cases, 140-150 Gy were irradiated using 4-mm collimators. Three different strategies were used. (1) Gamma thalamotomy as the primary surgical treatment. (2) As a secondary treatment, irradiation of the symmetric point of the contralateral selective thalamotomy. (3) Extension of the previous thalamotomy. For the first three cases (all PD), a special plug pattern (100 plugs) was used, but was not employed for the later cases. No acute untoward effects were noted, and overall there appeared to be a reduction in tremor. The time course of tremor reduction varied from case to case, from about 5-6 months to 1 year.

Adult↗
PubMed1996

Gamma Knife radiosurgery for acoustic schwannoma: effects of low radiation dose and functional prognosis.

The effects of relatively low dose Gamma Knife irradiation on acoustic schwannoma were evaluated in 29 patients followed over 2 years after treatment. The mean dose delivered to the tumor periphery was 12.1 Gy. Lowering of the magnetic resonance signal intensity in the tumor center appeared in 69% and signs of tumor shrinkage appeared in 59% of cases. The cyst in the tumor enlarged in 3 cases, and 2 cases developed hydrocephalus. The percentage of pure-tone hearing preservation was 82% at 3 months, 73% at 6 months, 68% at 12 months. 64% at 18 months and 59% at 24 months in 22 out of 29 cases. Relatively low dose Gamma Knife radiosurgery was effective in suppressing tumor growth, with preservation of hearing.

Adult↗
PubMed1996

Pathobiology of cerebral gliomas in children and the role of radiosurgery.

Twenty-five gliomas of the cerebral hemisphere in children were examined. Most hemispheric gliomas in children have relatively clear margins and less infiltrative potential. Radiosurgery has a role in the treatment of these tumors in addition to reducing the risk of radiation injuries developing later. Fifteen patients were alive 1-27 years (mean 8.4) following treatment and 10 patients died. Histologic examination demonstrated 10 differentiated gliomas, 10 poorly differentiated gliomas and 5 other gliomas. Most tumors had relatively clear margins on computed tomography and/or magnetic resonance images, and peritumoral edema was slight. In 9 autopsy cases, tumor dissemination and/or metastasis were seen in 7. However, tumor infiltration was not extensive, and clear tumor margins were found in some cases. Thus, cerebral gliomas in children have relatively clear margins and low infiltrative potential. Radiosurgery has a role in the treatment of these tumors.

Adolescent↗
PubMed1996

Grade II astrocytoma visualized by technetium-99m-ECD SPECT.

We present a case of primary brain tumor demonstrating increased uptake of 99mTc-ECD. Astrocytoma (Grade II) showed significantly increased cerebral blood perfusion on dynamic images and homogeneously increased uptake on static images with 99mTc-ECD brain SPECT. There seems to be some difference in perfusion and mechanism of tumor uptake among the cerebral blood flow imaging agents (99mTc-ECD, 99mTc-HMPAO and [123I]-IMP) and 201TI-chloride.

Adult↗
PubMed1995

Parkinsonian rigidity, dopa-induced dyskinesia and chorea--dynamic studies on the basal ganglia-thalamocortical motor circuit using PET scan and depth microrecording.

Regional cerebral glucose metabolism (rCMRGlu-18FDG) was measured in 6 cases with rigid type Parkinson's disease (PD) (2 cases with dopa-induced dyskinesia = DID), 6 cases with chorea (Ch), 5 cases with essential tremor (EssT) and 2 cases with normal subjects (N). The effects of L-Dopa on rCMRGlu was studied in 3 cases with PD. With the aid of depth microrecording study, stereotactic pallidotomy was performed in all cases with PD. Thalamotomy was performed in 3 cases with Ch. In the EssT and N group, the metabolic pattern was high in the frontal cortex (FCx) but low in the lenticular nucleus (LN). In contrast, all cases with a rigid type PD showed lower rCMRGlu in FCx (premotor, prefrontal area). However, 4 out of 6 cases were higher in LN than the control group. Administration of L-Dopa shifted rCMRGlu toward the normal pattern in this group. Five out of 6 cases with Ch represented higher rCMRGlu in FCx (3 focal, 2 diffuse) but lower in LN. Moreover, when DID occurred, it showed almost the same pattern as in Ch. Electrophysiological studies showed high background neuronal activity (BNA) in the medial segment of the globus pallidus (GP) but low BNA in the lateral segment of the GP in the rigid type of PD. In cases with Ch, irregular burst discharges were often encountered in ventro-oral thalamus. From these results, the on-going changes of basal ganglia-thalamocortical motor circuit in cases with a rigid type PD, DID and Ch are discussed. The underlying mechanisms of Parkinsonian rigidity was considered to contrast with those of DID and Ch within the same motor circuit.

Antiparkinson Agents↗
PubMed1995

Gamma Knife radiosurgery for the treatment of brainstem tumors.

Ten patients with brainstem tumors (BST) underwent Gamma Knife radiosurgery. In 5 cases, there were definitive histological diagnoses; ependymoma (n = 3) and CNS lymphoma (n = 2). The others were diagnosed as ependymoma (n = 1), CNS lymphoma (n = 2) and glioma (n = 2) on clinical grounds. Of 4 cases with ependymoma, the tumor showed a marked response in 3 cases. Of 4 cases with CNS lymphoma, all responded rapidly and the clinical symptoms improved markedly. However, in the 2 cases with glioma, the tumor remained unchanged or continued to grow. Gamma Knife radiosurgery was effective in local growth control of BST without adverse effects. An alternative treatment design will be required in glioma cases.

Adult↗
PubMed1995

Classification of arteriovenous malformations for radiosurgery. Neuroimaging, histopathology and radiobiologic effects.

Arteriovenous malformations (AVMs) were classified based on morphologic and hemodynamic factors. They were categorized as Moya type, shunt type or mixed type on the basis of hemodynamic factors, and as homogeneous or heterogeneous types on the basis of morphology. Histopathologic and radiobiologic characteristics were evaluated with respect to these AVM types. Classification depending on the type as well as the size of an AVM is important for modern treatment modalities, especially radiosurgery.

Cerebral Angiography↗
PubMed1995

Gamma Knife thalamotomy for the treatment of functional disorders.

Gamma Knife thalamotomy was performed with a 4-mm collimator in 2 cases with thalamic pain following a stroke and in 1 case of Parkinson's disease with tremor. In both cases with pain the maximum dose of 130 Gy was focused at the mediocaudal region of the previous thalamic lesion. In the case with tremor in Parkinson's disease, the maximum dose was 150 Gy. Longer follow-up is now proceeding, but the short-term results are encouraging. Based on data obtained from selective thalamotomy with depth microrecording, Gamma Knife thalamotomy could be a safe and effective technique for the treatment of these functional disorders.

Aged↗