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Biomedical subjects

M Samii

Publications and source records attributed to M Samii.

At least 127 records · Page 7Linked to original sources
PubMed1998

CSF dynamics in a rodent model of closed head injury.

Using ICP measurements and the bolus injection technique dynamic parameters of the cerebrospinal fluid system as there are pressure-volume-index (PVI) and resistance to CSF outflow (Rout) were investigated in a new model of diffuse closed head injury (CHI) in the rat. It was found that in the absence of brain oedema and ICP alterations an increase in PVI and Rout was present in the early (4h) period following head injury. This may be indicative for a reduction in cerebral blood flow and cerebral blood volume, both shown previously to occur after CHI. Furthermore an early impairment of CSF absorption mechanisms is evident. To answer the question, whether bolus injection techniques are advisable for clinical routine and whether results might have a predictive value, further investigations covering longer observation intervals and in the presence of secondary insults to the brain are necessary.

Animals↗
PubMed1998

Treatment of elevated intracranial pressure by infusions of 10% saline in severely head injured patients.

The management of intracranial pressure (ICP) is a factor in outcome of patients with head trauma. However, recent studies have revealed that the current strategies, which have been applied to control ICP for adequate cerebral perfusion, are unsatisfactory. Against this background, the efficacy of short-term infusions of hypertonic saline on ICP was investigated. In severely head injured (SHI) patients, hypertonic saline (100 ml 10% NaCl) was administered when standard agents (mannitol, sorbitol, THAM) failed in reducing ICP. To evaluate the pressure reduction after saline infusions the resulting ICP relaxations were analysed statistically in respect to the parameters amplitude, duration and dynamic behaviour of the ICP responses. In 42 randomized relaxations, the relative ICP decrease was 43% [28%-58%] (median [interquartile range]). The corresponding pressure drop was 18 mmHg [15-27 mm Hg]. Relaxations lasted for 93 min [64-126 min] and a relative ICP minimum was reached 26 min [12-33 min] after infusion. In the individual cases the temporal course of the parameters amplitude and decline interval depict a tendency toward lower and higher values, respectively, under conditions of a generally increasing ICP. As expected, the infusion of hypertonic saline reduces ICP in patients suffering from SHI. The pressure drop, duration and dynamic behaviour are suspected to depend both on the pressure level to reduce and concomitant medications.

Adolescent↗
PubMed1998

Time-dependent expression of donor- and host-specific major histocompatibility complex class I and II antigens in allogeneic dopamine-rich macro- and micrografts: comparison of two different grafting protocols.

Neural transplantation, as a therapeutic approach to Parkinson's disease, still requires allogeneic graft material and raises questions of immunosuppression and graft rejection. The present study investigated the time course of major histocompatibility complex (MHC) expression and astrocytic response in allogeneic dopaminergic grafts, comparing two different grafting protocols. Adult 6-hydroxydopamine-lesioned Lewis 1.W rats received intrastriatal cell suspension grafts from the ventral mesencephalon of DA rat fetuses, either as single 1-microliter macrograft via metal cannula or as four micrografts of 250 nl/deposit via a glass capillary. No immunosuppression was administered. Immunohistochemistry was performed at 1, 3, 6, and 12 weeks after grafting, using antibodies against donor- and host-specific MHC class I and II antigen, glial fibrillary acidic protein (GFAP) and tyrosine hydroxylase (TH). Most animals showed good allograft survival up to 12 weeks after transplantation with no signs of rejection. Reinnervation of the lesioned striatum by TH-positive neurites was observed from 3-6 weeks on. Expression of donor-specific MHC class I was comparably low in both allogeneic grafting groups, while host MHC class I and II reaction as well as astrocytic response tended to be higher in the macrografted animals. Donor MHC class II was not observed at any time point. It is concluded that intraparenchymal allografts of fetal mesencephalic cell suspensions can survive well in the rat Parkinson model without immunosuppression for at least 12 weeks, and that the expression of moderate amounts of donor-specific MHC class I antigen does not suffice to initiate a rejection process. In addition, the microtransplantation approach may reduce the level of trauma and subsequent MHC and GFAP expression and may, thereby, minimize the risk of graft rejection.

Animals↗
PubMed1998

An experimental approach to image guided skull base surgery employing a microscope-based neuronavigation system.

INTRODUCTION: A cadaveric study was undertaken to investigate the usefulness and reliability of a microscope based navigation system (NS) for skull base surgery. MATERIAL AND METHODS: CT-scans (1 mm slices) were performed in 10 fixed cadaver heads after implantation of fiducials. There upon, various skull base dissections were undertaken: transethmoidal-transsphenoidal approach to sella and clivus, retrosigmoidal approach to the internal auditory canal (IAC) and to the posterior semicircular canal (PSCC). The navigated dissections were performed with the MKM, a microscope based navigation system of Carl Zeiss (Oberkochen, Germany). RESULTS: The registration assessment by the NS yielded a mean deviation of 0.23 mm +/- 0.03 mm (mean +/- SD, n = 7, range 0.19 to 0.27 mm). The real anatomical deviation during dissection was 0.67 mm +/- 0.2 mm for navigation to the IAC and 0.71 mm +/- 0.37 mm to the PSCC. This accuracy was achieved with three fiducials (4 x 1 mm titanium screws) arranged as a triangle (side length 4-6 cm) nearby the surgical field. Navigation data on current position, direction and distance to a target structure were helpful in the transethmoidal-transsphenoidal approach to the clivus, as well as for accessing deep seated structures (C1-C2 junction, petrous bone tip). The contouring feature was beneficial for identifying structures embedded in the bone. However, due to inaccurate 3-D modelling this feature has a restricted reliability. DISCUSSION: Our cadaveric skull base study has shown that the MKM is a reliable tool with high anatomical accuracy and usefulness of most navigation features. However, in order to effectively and reliably use any NS the surgeon must be familiar with its potential features and limitations as is demonstrated in this study.

Equipment Design↗
PubMed1998

Sinusoidal intrathecal infusion for assessment of CSF dynamics in kaolin-induced hydrocephalus.

OBJECTIVE: To evaluate whether changes of CSF outflow resistance and compliance in hydrocephalus can be assessed by an intrathecal infusion which is performed at a sinusoidal varying rate. METHODS: Hydrocephalus was produced in 10 Sprague Dawley rats by instillation of 0.0375 g of kaolin in 0.9% saline into the cisterna magna. Measurements were performed 4 weeks later: With each animal both, three successive constant rate infusions (0-0.02 ml/min) and a sinusoidal infusion (0-0.02 ml/min, frequency 0.006 Hz) were performed. 6 normal animals served as control. The pressure recordings of both infusion techniques were used for the assessment of the CSF outflow resistance. The time constant and the pressure volume index were calculated only from the sinusoidal input testing. RESULTS: The sinusoidal test as well as the constant rate infusion both demonstrated a severe impairment of CSF absorption. By the sinusoidal input, a decreased compliance was confirmed additionally. Thus, the sinusoidal infusion test demonstrated a high resistance and low compliance hydrocephalus in the kaolin-treated group. A simple graphical procedure is presented which allows an easy assessment of CSF dynamics by the sinusoidal infusion test.

Animals↗
PubMed1998

Differences in acquisition and full performance in skilled forelimb use as measured by the 'staircase test' in five rat strains.

Skilled forelimb use was examined in five different rat strains (DA/Ztm, LEW/Ztm-ci, LEW.1W/Ztm, SD/Ztm, SPRD/Ztm-Cu3) by means of the 'staircase test', as originally described by Montoya et al. [20] (C.P. Montoya, H.L. Campbell, K.D. Pemberton, S.B. Dunnett, The 'staircase test': A measure of independent forelimb reaching and grasping abilities in rats, J. Neurosci. Methods 36 (1991) 219-228). Strain-dependent differences were observed most prominently during the acquisition phase, and less pronounced, at the full performance level. SD/Ztm and DA/Ztm rat strains seemed to be particularly skilled in their forelimb use, although with varying levels of activity. Interestingly, significant differences in skilled forelimb movements were found between the related Sprague-Dawley derived and Lewis congenic rat strains. No clear-cut correlation was found between skilled forelimb use and basic nutrition-dependent measures, such as pretest body weight or weightloss during the test period. Based on previous observations on strain-dependent behavioral variations it seems likely that the differences in skilled forelimb use, as observed in the present study, might be caused by morphological and/or functional strain-dependent alterations in the involved neuronal circuitries, such as motor cortex, caudate-putamen unit and mesotelencephalic dopamine system. However, they should also be considered as potentially influencing parameters in studies related to the behavioral effects of lesions and restorative therapies in the central nervous system.

Animals↗
PubMed1998

Ossified and de novo cavernous malformations in the same patient.

We report the case of a 44-year-old patient with a MRI scan showing a newly developed cavernoma after two highly calcified lesions had been excised surgically. Six other cavernous malformations had been followed by MR imaging over a 2-year period. The coexistence of the two extremes of cavernous malformations in terms of lesions development--de novo and ossified lesions has not been reported previously and has implications for both the follow-up and the natural history of these malformations. The potential for developing new cavernous malformations persists and does not seem to be related to the evolutional stage of pre-existing lesions. It is suggested that these patients need to be followed up by MRI on a regular basis.

Adult↗
PubMed1998

Direct magnification technique for cerebral angiography in the rat.

RATIONALE AND OBJECTIVES: The authors evaluated the performance of direct magnification radiography (DIMA) with digital image processing for cerebral angiography in the rat. METHODS: A microfocal x-ray unit with a focal spot of 5 microns was used for cerebral angiography in 10 rats. The animals were examined form x 4 up to x 20 magnification after injection of 0.2 mL x-ray contrast medium into the common carotid artery. RESULTS: Direct magnification radiography technology provides high resolution images and enables the visualization of very small vessels with high quality. It allows the peripheral branches of the middle cerebral artery or the ophthalmic artery to be visualized. Superimposition and noise effects can be excluded with digital subtraction and image processing. CONCLUSIONS: The experiments show that DIMA radiography is a suitable technique for cerebral angiography in the rat.

Animals↗
PubMed1998

Surgery of spinal nerve sheath tumors with special reference to neurofibromatosis.

OBJECTIVE: We conducted a retrospective study of 87 patients with spinal nerve sheath tumors to determine the overall clinical outcome and specific features in 20 patients affected with neurofibromatosis Types 1 and 2 (NF-1 and NF-2, respectively). METHODS: Case records, operation notes, outpatient files, and radiological examinations were analyzed for all patients treated between September 1977 and August 1994. Additional follow-up data were obtained using outpatient examinations, questionnaires, and telephone calls. RESULTS: During the study period, 128 spinal neuromas (i.e., schwannomas) and 6 neurofibromas in 87 patients were treated. Fifty-seven neuromas were associated with NF-2 in 17 patients and six neurofibromas with NF-1 in 3 patients. Patients with NF-2 and symptomatic neuromas presented with more severe neurological deficits compared to patients without NF-2. Eighty-six percent of the neuromas were removed completely. On average, most preoperative deficits or symptoms improved in patients without NF-2, whereas neurological symptoms remained unchanged in patients with NF-2. Multiple regression analysis revealed that partial removal, surgery of a recurrent tumor, NF-2, and old age predisposed for tumor recurrence. No increased risk of recurrence was observed for patients with NF-1. For patients without NF-2, we observed overall recurrence rates of 10.7% after 5 years and 28.2% after 10 and 15 years, respectively, as determined by Kaplan-Meier analysis. For NF-2, the recurrence rate at 5 years was 39.2%, and all tumors had recurred by 9 years. CONCLUSION: Spinal nerve sheath tumors carry an excellent prognosis in patients with NF-1 and in patients without neurofibromatosis. Symptomatic neuromas occurring in association with NF-2 present with more severe neurological deficits, demonstrate little postoperative improvement, and have a very high recurrence rate.

Adolescent↗
PubMed1998

PET and CBF studies of chronic hydrocephalus: a contribution to surgical indication and prognosis.

The authors investigate whether measurement of cerebral blood flow (CBF) in chronic hydrocephalus is a reliable indicator in selecting patients to undergo ventriculoperitoneal shunting. Global and regional CBF is quantified (Kety-Schmidt one-compartment model) by positron emission tomography in 21 patients. CBF is determined following injection of 15O-H2O at three time points: 1 week before, 7 days after, and 7 months after shunting. The neurological status of these patients is classified, and cerebrospinal fluid (CSF) dynamics continuous intracranial pressure [ICP] monitoring and CSF infusion tests) were assessed prior to surgery. Preoperative global CBF values correlate well with clinical outcome. Patients with a significantly lower global CBF value show clinical improvement after 7 months, whereas patients with higher CBF values do not (mean, 33 vs. 45 ml/100 ml per minute; p < 0.05). In contrast to conventional methods, including long-term ICP measurement and CSF infusion tests, preoperative global CBF values are discriminating in terms of clinical outcome. Thus, measurement of CBF may be helpful in evaluating the ultimate utility of shunt therapy in chronic hydrocephalus.

Aged↗
PubMed1998

Microvascular decompression for superior oblique myokymia: first experience. Case report.

Superior oblique myokymia (SOM) is a rare eye movement disorder presenting as uniocular rotatory microtremor due to intermittent contractions of the superior oblique muscle. Medical treatment usually fails to provide long-term benefit for the patient and has considerable side effects. Surgical alternatives including tenotomy or partial tenectomy of the superior oblique tendon often result in incomplete resolution of the visual symptoms. The authors report a patient who experienced immediate cessation of disabling SOM following microvascular decompression of the fourth nerve at the root exit zone. Temporary double vision at downgaze resolved 5 months after surgery. There was no recurrence of oscillopsia during a follow-up of 22 months to date. From this single observation it appears likely that vascular compression of the trochlear nerve could be a significant pathophysiological factor contributing to SOM. In the hands of an experienced surgeon, microvascular decompression at the brainstem exit zone of this nerve may evolve as the method of choice for selected cases of disabling SOM.

Decompression↗
PubMed1998

Dopaminergic graft-induced long-term recovery of complex sensorimotor behaviors in a rat model of Parkinson's disease.

Transplantation of embryonic dopamine neurons has evolved as an alternative neurosurgical treatment strategy for patients with Parkinson's disease and it is therefore of great interest to further optimise this procedure in experimental studies. We have applied a modified microtransplantation approach in unilaterally 6-hydroxydopamine lesioned rats and observed a substantial and long-lasting functional recovery in complex spontaneous behaviors, such as skilled forelimb use and stepping behavior. The results demonstrate that the rat model of Parkinson's disease is a highly useful tool to study mechanisms of neural plasticity and regeneration. The ability of dopaminergic grafts to restore complex sensorimotor behaviors in animals also indicate their great potential for the development of a successful clinical application.

Animals↗
PubMed1997

Hemispheric asymmetries in spontaneous firing characteristics of substantia nigra pars reticulata neurons following a unilateral 6-hydroxydopamine lesion of the rat nigrostriatal pathway.

Single unit activity of substantia nigra pars reticulata (SNR) neurons was recorded bilaterally in rats subjected to unilateral 6-hydroxydopamine lesions of the ascending mesostriatal dopaminergic pathway, resulting in an almost complete loss of dopaminergic neurons in the ipsilateral SN pars compacta. Firing rate and firing pattern of SNR neurons in lesioned rats were compared with respective data from sham-lesioned rats and naive controls. In lesioned rats, the mean firing rate of SNR neurons at the lesioned side was significantly reduced and there was an increase in the occurrence of bursting activity. In contrast, firing rate in the contralateral SNR was significantly increased without change in the frequency of bursting neurons. This asymmetrical change in spontaneous firing characteristics of SNR neurons following the lesion could be involved in the complex behavioral changes seen in this model of Parkinson's disease.

Animals↗
PubMed1997

[Diagnosis and surgical indications of traumatic brachial plexus lesions from the neurosurgery viewpoint].

The precise preoperative clinical and electrophysiological evaluation of the brachial plexus as well as an exact radiological evaluation are the keystones for the treatment of traumatic injuries of the brachial plexus. Furthermore, surgical management and prognosis of traction injuries of the brachial plexus depend on the accurate diagnosis of root avulsion from the spinal cord. Myelography, myelo-computed tomography and recently magnetic resonance imaging are the main radiological methods for preoperative diagnose of cervical root avulsions. Surgical experience shows that in may cases, extraspinal findings diverge from intradural findings. Consequently, only correlation with the intradural surgical findings will allow us to define the factual accuracy of myelo-CT and MRI studies. Accuracy of the preoperative myelo-CT based diagnosis related to the intraoperative intradural findings was 85% On the other hand, MRI showed an accuracy of only 52%. Therefore, myelo-CT scans with 1 to 3 mm axial slices proves to be the most reliable method to evaluate preoperatively the presence of complete or partial root avulsion in traumatic brachial plexus injuries. However in 15% of the cases preoperative exact radiological diagnosis is unfortunately not reliable. In these special cases intraspinal surgical exposure of the cervical roots will provide the accurate diagnosis of root avulsion. Accurate clinical evaluation and exact assessment of intraspinal root avulsion simplify enormously the decision concerning the choice of donor nerves for transplantation and/or neurotization during brachial plexus surgery.

Brachial Plexus↗
PubMed1997

[Nerve transfer (neurotization) for functional reconstruction of arm functions in cervical root avulsions].

Neurotization procedures represent an important therapeutic option in patients with complete root avulsion due to traumatic brachial plexus injuries. A variety of normal donor nerves can be used, including intercostal nerves, accessory nerve, parts of the cervical plexus, phrenic nerve, and/or the contralateral C7 nerve root. The reconstructive neurotization procedure should be performed within 3-6 months following the trauma and, when successful, can lead to substantial improvement in motor function for the shoulder and upper arm and in sensory function for the forearm, hand and finger region. Neurotization can also be combined with neurolysis and/or transplantation to restore upper limb motor and sensory function in order to achieve greater therapeutic benefit for patients with posttraumatic brachial plexus lesions.

Arm↗
PubMed1997

[Nerve transplantation and neurolysis of the brachial plexus after post-traumatic lesions].

Autologous transplantation in brachial plexus injuries has become significantly more efficacious through increased knowledge of the microtopographic anatomy of the fascicle structures and the refinement of microneurosurgical techniques. Recovery of shoulder and upper arm functions can be achieved with autologous transplantation in the majority of patients under optimized conditions. However, attempts to restore forearm, hand and finger functions in this way have been disappointing so far. Therapeutic success is primarily governed by early decision making, selection of adequate surgical strategies and intensive and longlasting postoperative management.

Arm↗
PubMed1997

[Pain management after post-traumatic brachial plexus lesions. Conservative and surgical therapy possibilities].

The occurrence of sever pain is one of the most disabling symptoms after the traumatic lesion of the brachial plexus. Avulsion of one or more cervical roots of the brachial plexus is the main cause of severe pain, known as deafferentation pain. Lesion of the dorsal horn of the cervical spinal cord due to root avulsion may lead to important pathological changes and scarring that are responsible for the induction of pain sensations. Different medical and surgical treatment modalities have been established to relief such pain after brachial plexus injury. In contrast to drug therapy, which usually offers only limited benefit, surgical treatment over the last years has shown positive results. Coagulation of the dorsal root entry zone (DREZ) is one of the most efficient surgical treatments for these patients. Understanding of the pathophysiological changes and different pain mechanisms induced by traumatic injury of the brachial plexus is fundamental for the planning and step-wise treatment of such patients.

Brachial Plexus↗