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Biomedical subjects

M Brock

Publications and source records attributed to M Brock.

At least 37 records · Page 2Linked to original sources
PubMed2002

Impact of brain shift on intraoperative neurophysiological monitoring with cortical strip electrodes.

BACKGROUND: Intraoperative neurophysiological monitoring has become the standard procedure for locating eloquent regions of the brain. Such continuous electrical stimulation of motor pathways is usually applied by means of flat silicon-embedded electrodes placed directly on the motor cortex. However, shifting of the silicon strip on the cortical surface as well as electrode displacement due to brain shift underneath the electrode can lead to inaccurate recordings not directly caused by intraoperative impairment of the motor cortex or the motor pathways. METHOD: This prospective study was conducted to quantify cortical brain shift during open cranial surgery and to assess its impact on electrode positioning in 31 procedures near the precentral gyrus. Three groups of different lesion volumes were distinguished. Movement of the cortex between opening of the dura and completion of tumor removal as well as cortical electrode shifting were digitally measured and analyzed. FINDINGS: Cortical surface structures evidenced a significantly larger shift (up to 23.4 mm) in comparison to the electrode strips (up to 4.2 mm) in lesions with a volume of over 20 ml. Cortex shifting highly correlated with lesion volume, whereas strip electrode movement was almost unidirectional and did not differ significantly among the three groups. However, the way they were placed (completely on the cortex vs. partly underlying or overlapping the craniotomy borders) affected the magnitude of their intraoperative displacement. As a consequence, 3 of the 31 cases (9.3%) showed a significant change in the recorded motor responses due to intraoperative dislocation of the stimulating electrode. INTERPRETATION: Changes in the location of cerebral structures due to intraoperative brain shift may exert a marked influence on intraoperative neurophysiological monitoring if cortical strip electrodes are used. Therefore, long-term monitoring of the central region requires continuous checking of the position of stimulating electrodes and, if necessary, correction of their location.

Adult↗
PubMed2002

Spontaneous bilateral chronic subdural haematoma of the posterior fossa. Case report and review of the literature.

INTRODUCTION: Chronic subdural haematomas of the posterior fossa in adults without a history of trauma are very rare. To our knowledge, only 15 cases have so far been reported in the literature, including those with anticoagulation therapy. A case of spontaneous bilateral infratentorial chronic subdural haematoma associated with anticoagulation therapy in an alive adult is presented and the relevant literature is reviewed. CASE REPORT: A 70 year old female presented with progressive dizziness, vertigo and gait ataxia. She was on anticoagulation therapy for heart disease. Neuro-imaging revealed bilateral infratentorial subdural masses. The subdural masses were suspects for chronic subdural haematomas by neuroradiological criteria. Because of the progressive symptomatology, the haematomas were emptied through burrhole trepanations. Chocolate-colored fluid, not containing clotted components, gushed out under great pressure. The source of bleeding could not be identified. The patient recovered well from surgery, but died 4 months later shortly after admission to another hospital from heart failure. DISCUSSION: The chronic subdural haematomas in this patient may have been due to rupture of bridging veins caused by a very mild trauma not noticed by the patient and possibly aggravated by the anticoagulation therapy. Infratentorial chronic subdural haematoma should at least be a part of the differential diagnosis in elderly patients with cerebellar and vestibular symptomatology even without a history of trauma.

Aged↗
PubMed2002

Results of chronic subthalamic nucleus stimulation for Parkinson's disease: a 1-year follow-up study.

BACKGROUND: Deep brain stimulation (DBS) has been established as an alternative approach for the treatment of advanced Parkinson's disease (PD). Recently, the subthalamic nucleus (STN) has been identified as the optimal target for DBS. METHODS: Thirty-eight patients have undergone surgery for advanced PD since 1996. They include 12 females and 26 males with a mean age of 55.6 years. The mean stage on the Hoehn and Yahr Scale was 3.5 (off condition). Electrodes (Medtronic DBS 31389) were stereotactically implanted into the STN bilaterally. Targeting was performed using computerized tomography (CT) scans and ventriculography (VG). After 4 days of external stimulation, permanent neurostimulators were implanted. Patients were evaluated preoperatively and 1, 6, and 12 months postoperatively. Evaluations were performed in defined on and off states using the Unified Parkinson's Disease Rating Scale (UPDRS) as well as the Hoehn and Yahr Scale, the dyskinesia scale, and the Activities of Daily Living (ADL) Scale. RESULTS: Significant improvement of all motor symptoms was found in all patients (UPDRS motor score 32/48 preoperatively versus 15/30 at 12-month follow-up, p < 0.001). Daily off-times were reduced by 35%. Dyskinesias also improved markedly (UPDRS IV: 3.2/3.1 [on/off] vs. 0.9/1.3 at 12 months follow-up). Postoperative L-dopa medication was adjusted (mean reduction: 53%). Complications occurred in two patients (5%) who developed infections, leading to system removal. Systems were replaced after 6 months. Two patients (5%) had a permanent worsening of a previously known depressive state and developed progressive dementia. CONCLUSIONS: TN stimulation is a relatively safe procedure for treating advanced PD. The possibility of readjusting the stimulation parameters postoperatively improves the therapeutic outcome and reduces side effects in comparison to ablative methods.

Electric Stimulation Therapy↗
PubMed2002

[Cost analysis of intraoperative neurophysiological monitoring (IOM)].

INTRODUCTION: A number of studies demonstrate that a significant reduction of postoperative neurological deficits can be achieved by applying intraoperative neurophysiological monitoring (IOM) methods. A cost analysis of IOM is imperative considering the strained financial situation in the public health services. MATERIAL AND METHODS: The calculation model presented here comprises two cost components: material and personnel. The material costs comprise consumer goods and depreciation of capital goods. The computation base was 200 IOM cases per year. Consumer goods were calculated for each IOM procedure respectively. The following constellation served as a basis for calculating personnel costs: (a) a medical technician (salary level BAT Vc) for one hour per case; (b) a resident (BAT IIa) for the entire duration of the measurement, and (c) a senior resident (BAT Ia) only for supervision. RESULTS: An IOM device consisting of an 8-channel preamplifier, an electrical and acoustic stimulator and special software costs 66,467 euros on the average. With an annual depreciation of 20%, the costs are 13,293 euros per year. This amounts to 66.46 euros per case for the capital goods. For reusable materials a sum of 0.75 euro; per case was calculated. Disposable materials were calculate for each procedure respectively. Total costs of 228.02 euro; per case were,s a sum of 0.75 euros per case was calculated. Disposable materials were calculate for each procedure respectively. Total costs of 228.02 euros per case were, calculated for surgery on the peripheral nervous system. They amount to 196.40 euros per case for spinal interventions and to 347.63 euros per case for more complex spinal operations. Operations in the cerebellopontine angle and brain stem cost 376.63 euros and 397.33 euros per case respectively. IOM costs amount to 328.03 euros per case for surgical management of an intracranial aneurysm and to 537.15 euros per case for functional interventions. Expenses run up to 833.63 euros per case for operations near the motor cortex and to 117.65 euros per case for intraoperative speech monitoring. DISCUSSION: Costs for inpatient medical rehabilitation have increased considerably in recent years. In view of the financial situation, it is necessary to reduce postoperative morbidity and the costs it involves. IOM leads to a reduction of morbidity. The costs for IOM calculated here justify its routine application in view of the legal and socioeconomic consequences of surgery-related neurological deficits.

Algorithms↗
PubMed2001

Ultrastructural changes in paravertebral muscles associated with degenerative spondylolisthesis.

STUDY DESIGN: The paravertebral muscle of 30 patients with spondylolisthesis and 30 control patients were investigated histologically. OBJECTIVE: To propose myopathologic paravertebral muscle changes in cases of degenerative lumbar spondylolisthesis. SUMMARY OF BACKGROUND DATA: The stability of the vertebral column is based on both active and passive systems. The passive system is composed of the vertebrae, the intervertebral discs, and the ligaments. Surrounding muscles and tendons constitute the active system. The autochthonous back muscles take over support functions if the passive system is ineffective. In some cases, muscles are overstrained for a long period, ultimately leading to muscular changes. This study was performed to determine the histopathologic correlates of this permanent strain. METHODS: Between July 1998 and July 1999, paravertebral muscle biopsies were performed for 30 patients with monosegmental degenerative spondylolisthesis undergoing posterior lumbar interbody fusion. The tissue samples were submitted to histologic analysis including immune and enzyme histochemistry and electron microscopy. In addition, the muscle fibers were submitted to morphometry. RESULTS: Severe pathologic alterations were found. The findings showed that 22 patients (73.3%) had ragged red fibers with evident ultrastructural mitochondrial anomalies. The cristae appeared irregular in 12 patients (40%) Type 1 paracrystalline inclusions were detected in five samples (16.6%) and dense bodies in eight (26.6%). Fibers with ubiquitin-positive inclusions were detected by immunohistochemistry in 13 patients (43.3%). As shown by the electron microscope, these corresponded to granulofilamentous inclusions and polyglucosan bodies. The samples were submitted to genetical analysis because biochemical studies showed reduced activity of the respiratory chain enzymes. Normal mitochondrial deoxyribonucleic acids of unchanged length were detected. CONCLUSIONS: Apart from nonspecific myopathic changes such as those observed in rimmed vacuoles and rods, increased numbers of polyglucosan bodies were detected. This increase in polyglucosan bodies currently has not been described in patients with otherwise normal muscles.

Adult↗
PubMed2001

Aspergillus nidulans DigA, a potential homolog of Saccharomyces cerevisiae Pep3 (Vps18), is required for nuclear migration, mitochondrial morphology and polarized growth.

The fungal vacuole is an acidic organelle that is involved in a variety of physiological processes, such as protein turnover, ion and pH homeostasis and osmoregulation. The function of the vacuole largely depends on vesicle transport providing the organelle with enzymes and substrates. The process of vesicle transportation has been studied best in Saccharomyces cerevisiae, where several proteins that are crucial for intracellular vesicle sorting have been identified. One such protein is Pep3 (Vps18). In pep3 mutants vacuole function and vacuole morphology are affected. We cloned the gene for a potential homolog of Pep3 from the filamentous fungus Aspergillus nidulans. The gene, digA (for dichotomous growth), was identified in a screen for nuclear migration mutants. A. nidulans digA encodes a protein of 108.3 kDa, which includes a 122-amino acid clathrin repeat motif, two short coiled-coil regions, and a RING finger Zn-binding motif at the C-terminus. All three sequence motifs suggest interaction of DigA with other proteins. DigA is 25% identical to a homolog from Schizosaccharomyces pombe, 23% to a protein from human, 21% to the product of the Drosophila melanogaster gene deep orange (dor) and 18% to S. cerevisiae Pep3 (Vps18). We localized DigA as a HA-epitope-tagged protein in the cytoplasm of A. nidulans vegetative cells, by secondary immunofluorescence. A digA mutant displays a pleiotropic phenotype with clustered mitochondria, clustered nuclei and a defect in polarization of the actin cytoskeleton. These results suggest that vacuolar functions are required for organelle positioning and polarized growth.

Adaptor Proteins, Vesicular Transport↗
PubMed2001

[Neurosurgical therapy of Parkinson disease. Deep brain stimulation].

The introduction of continuous high frequency stimulation (deep brain stimulation) into functional neurosurgery has opened up new avenues in the treatment of Parkinson's disease. This new technique expands the therapeutic possibilities available to those patients in whom, over the years, the effectiveness of drug treatment has deteriorated, or severe side effects developed. In the individual case, the decision as to whether to operate is taken on the basis of interdisciplinary cooperation between the care-providing neurologist and the neurosurgeon specialized in this particular field.

Basal Ganglia↗
PubMed2001

Intracranial image-guided neurosurgery: experience with a new electromagnetic navigation system.

BACKGROUND: The aim of image-guided neurosurgery is to accurately project computed tomography (CT) or magnetic resonance imaging (MRI) data into the operative field for defining anatomical landmarks, pathological structures and tumour margins. To achieve this end, different image-guided and computer-assisted, so-called "neuronavigation" systems have been developed in order to offer the neurosurgeon precise spatial information. METHOD: The present study reports on the experience gained with a prototype of the NEN-NeuroGuard neuronavigation system (Nicolet Biomedical, Madison, WI, USA). It utilises a pulsed DC electromagnetic field for determining the location in space of surgical instruments to which miniaturised sensors are attached. The system was evaluated in respect to its usefulness, ease of integration into standard neurosurgical procedures, reliability and accuracy. FINDINGS: The NEN-system was used with success in 24 intracranial procedures for lesions including both gliomas and cerebral metastases. It allowed real-time display of surgical manoeuvres on pre-operative CT or MR images without a stereotactic frame or a robotic arm. The mean registration error associated with MRI was 1.3 mm (RMS error) and 1.5 mm (RMS error) with CT-data. The average intra-operative target-localising error was 3.2 mm (+/- 1.5 mm SD). Thus, the equipment was of great help in planning and performing skin incisions and craniotomies as well as in reaching deep-seated lesions with a minimum of trauma. INTERPRETATION: The NEN-NeuroGuard system is a very user-friendly and reliable tool for image-guided neurosurgery. It does not have the limitations of a conventional stereotactic frame. Due to its electromagnetic technology it avoids the "line-of-sight" problem often met by optical navigation systems since its sensors remain active even when situated deep inside the skull or hidden, for example, by drapes or by the surgical microscope.

Adult↗
PubMed2001

2-Methylisocitrate lyases from the bacterium Escherichia coli and the filamentous fungus Aspergillus nidulans: characterization and comparison of both enzymes.

In Escherichia coli and Aspergillus nidulans, propionate is oxidized to pyruvate via the methylcitrate cycle. The last step of this cycle, the cleavage of 2-methylisocitrate to succinate and pyruvate is catalysed by 2-methylisocitrate lyase. The enzymes from both organisms were assayed with chemically synthesized threo-2-methylisocitrate; the erythro-diastereomer was not active. 2-Methylisocitrate lyase from E. coli corresponds to the PrpB protein of the prp operon involved in propionate oxidation. The purified enzyme has a molecular mass of approximately 32 kDa per subunit, which is lower than those of isocitrate lyases from bacterial sources ( approximately 48 kDa). 2-Methylisocitrate lyase from A. nidulans shows an apparent molecular mass of 66 kDa per subunit, almost equal to that of isocitrate lyase of the same organism. Both 2-methylisocitrate lyases have a native homotetrameric structure as identified by size-exclusion chromatography. The enzymes show no measurable activity with isocitrate. Starting from 250 mM pyruvate, 150 mM succinate and 10 microM PrpB, the enzymatically active stereoisomer could be synthesized in 1% yield. As revealed by chiral HPLC, the product consisted of a single enantiomer. This isomer is cleaved by 2-methylisocitrate lyases from A. nidulans and E. coli. The PrpB protein reacted with stoichiometric amounts of 3-bromopyruvate whereby the activity was lost and one amino-acid residue per subunit became modified, most likely a cysteine as shown for isocitrate lyase of E. coli. PrpB exhibits 34% sequence identity with carboxyphosphoenolpyruvate phosphonomutase from Streptomyces hygroscopicus, in which the essential cysteine residue is conserved.

Amino Acid Sequence↗
PubMed2001

Neurosurgical procedures in Jehovah's Witnesses: an increased risk?

OBJECTIVE: Because of the growing numbers of members worldwide in the sect of Jehovah's Witnesses, the refusal of blood and blood products due to religious reasons is increasingly encountered in clinical practice. As an alternative to blood transfusion, Jehovah's Witnesses accept blood-free volume substitution, and they sometimes accept the intraoperative reinfusion of autologous blood via a so-called cell saver. The aim of this study was to examine whether the refusal of blood transfusion affects the surgical indications for neurosurgery and whether morbidity and mortality rates are higher after neurosurgical interventions in Jehovah's Witnesses. METHODS: The pre-, intra-, and postoperative hemoglobin and hematocrit values as well as coagulation parameters of a group of Jehovah's Witnesses (n = 103) were compared with those of a valid control group. RESULTS: The total intraoperative blood loss during spinal and intracranial surgery in Jehovah's Witnesses was often less than in controls, which suggests a less traumatic surgical procedure. Hemodynamically relevant blood loss occurred in two spinal and four intracranial interventions. The patients were managed without receiving blood transfusions or blood products, although increased time in the intensive care unit and increased convalescence days were necessary. Mean surgical times were 17.5 minutes longer for spinal interventions and 36.7 minutes longer for intracranial interventions than for patients in the control group. This may be attributed to a more careful and thus slower surgical technique and to longer and more extensive hemostasis. The length of hospitalization was 15% longer for Jehovah's Witnesses than for controls. CONCLUSION: The morbidity and mortality rates for Jehovah's Witnesses undergoing neurosurgery were not higher than those of the control group. Thus, it can be concluded that Jehovah's Witnesses did not have a higher risk when microsurgical techniques and extensive anesthetic monitoring were applied during neurosurgery. Because the surgical success rate for Jehovah's Witnesses corresponded to that of the control group, the increase in costs because of longer treatment times is compensated in the long run by avoiding a lengthier illness, sometimes with more expensive conservative therapy.

Adolescent↗
PubMed2001

Lumbar disc herniation in patients up to 25 years of age.

Retrospective analysis of 165 patients (105 males, 60 females) with a mean age of 21.2 years (range 14 to 25 years) of 6933 surgically treated patients from January 1987 to May 1999 focused on age and sex distribution, body mass, familial predisposition, trauma, histology, and clinical course. The incidence of herniated lumbar discs was 2.3% in patients aged up to 25 years. A valid family history was obtained in 121 patients and a positive history was found in 82 of these patients (67.8%). The patients had a higher body mass index compared to a group of individuals with a similar age structure. Radiography demonstrated bony changes in 124 patients (75.2%), primarily attributable to postural deformities such as scoliosis. The condition of the bony structures seems to be more important than the condition of the disc tissue in the occurrence of this disease in young patients.

Adolescent↗
PubMed2001

Monitoring of intraoperative motor evoked potentials to increase the safety of surgery in and around the motor cortex.

OBJECT: The repetitive application of high-frequency anodal monopolar stimulation during surgery in or near the motor cortex allows a qualitative and quantitative evaluation of motor evoked potentials (MEPs). Using this method, motor pathways and motor function can be continuously monitored during surgery. METHODS: In this prospective study, 70 patients underwent MEP monitoring during surgery performed in the central region. All procedures were performed after general anesthesia had been induced without the aid of muscle relaxants. The motor pathways were monitored during the entire surgical procedure by repetitive high-frequency anodal monopolar stimulation (frequency 400-500 Hz; train 7-10 pulses; impulse duration 0.2-0.7 msec; and stimulation intensity 16.9 +/- 7.76 mA). The MEPs were continuously evaluated to assess their latency, potential duration, and amplitude. Recorded alterations in these parameters were subsequently correlated with surgical maneuvers and with postoperative neurological deterioration. The monitoring parameters (latency, potential duration, and amplitude) had a broad interindividual range of variation. A correlation between individual intraoperative changes in the potentials and surgical maneuvers or postoperative neurological deterioration was observed in eight cases. A spontaneous shift in latency greater than 15% or a sudden reduction in the amplitude of the potential greater than 80% was considered a warning criterion. In all cases in which there was an irreversible change in latency or a complete loss of potentials were observed, there was postoperative neurological deterioration. CONCLUSIONS: Improved surgical safety can be achieved using intraoperative neurophysiological monitoring procedures. Repetitive stimulation of the motor cortex proved to be a reliable method for monitoring subcortical motor pathways. Changes in MEP latency and MEP amplitude served as warning criteria during surgery and possessed prognostic value.

Adolescent↗
PubMed2001

Has nonoperative management of solid visceral injuries adversely affected resident operative experience?

The purpose of this study was to assess the impact of increased use of nonoperative management of blunt injuries to the spleen or liver on surgical residents' operative experience with solid visceral injuries. We conducted a 10-year retrospective study of blunt spleen and liver injuries at a state-designated Level I trauma center and a survey of chief residents' operative experience with splenic and hepatic injuries from blunt trauma during the same time period. From 1990 through 1999, 431 patients were admitted with splenic injuries and 634 patients were admitted with liver injuries; 350 splenic injuries (81%) were due to blunt trauma; 317 liver injuries (50%) were caused by blunt mechanisms. In 1990 100 per cent of patients with splenic injuries and 93 per cent of those with liver injuries underwent surgery for those injuries. These rates were 19 and 28 per cent respectively in 1999. The number of patients with blunt solid visceral injuries increased more than fourfold from 1990 through 1999. The number of operations for splenic and hepatic injuries performed by chief residents did not decline significantly during this time period (5.5 cases per chief resident in 1990; 4.6 cases per chief resident in 1999). The increased numbers of patients with solid visceral injuries were due to two factors: increased proportion of blunt trauma admissions especially from motor vehicle collisions and improved recognition of spleen and liver injuries by expanded use of CT scans. We conclude that nonoperative management of blunt solid visceral injuries does not necessarily lead to a diminution of operations nor jeopardize resident education. However, trauma volumes must be high enough to support adequate operative experience.

Accidents, Traffic↗
PubMed2000

Intracranial haemorrhage following lumbar myelography: case report and review of the literature.

We describe a subacute intracranial subdural haematoma following lumbar myelography. This rare but potentially life-threatening complication has been reported both after lumbar myelography and following lumbar puncture for spinal anaesthesia. We review 16 previously reported cases of intracranial haemorrhage following lumbar myelography, and discuss the pathogenesis. In all reported cases post-puncture headache was the leading symptom and should therefore be regarded as a warning sign.

Cerebral Angiography↗