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Biomedical subjects

M Brock

Publications and source records attributed to M Brock.

At least 55 records · Page 3Linked to original sources
PubMed2000

Intra-operative mapping of the motor cortex during surgery in and around the motor cortex.

The intra-operative use of neurophysiological techniques allows reliable identification of the sensorimotor region, and constitutes a prerequisite for its anatomical and functional preservation. The present prospective study combines monopolar cortical stimulation (MCS) with the recording of phase reversal of somatosensory evoked potentials (SEP-PR) in a protocol for the intra-operative mapping of the motor cortex. Functional mapping of the motor cortex by SEP-PR and MCS was performed in 70 patients during surgery in and around the motor cortex. The central sulcus was identified by SEP-PR. Cortical motor mapping was then performed by monopolar anodal (400 Hz) stimulation. Motor responses were recorded by needle electrodes placed in the muscles of the contralateral extremities. Surgery was performed under general anaesthesia without muscle relaxants. Intra-operative localization of the central sulcus by SEP-PR was possible in 68 patients (97.14%). Motor evoked potentials (MEP) were elicited following MCS in 67 cases (95.7%). In 3 cases no MEP was recorded, not even after maximal stimulation intensity, the central sulcus being localized by SEP-PR only. On the other hand, MCS allowed localizing the motor cortex in the 2 cases with no recordable SEP-PR. Thus, combining SEP-PR and MCS allowed intra-operative localization of the sensorimotor cortex in 100% of the cases.

Adolescent↗
PubMed2000

A new cortical electrode for neuronavigation-guided intraoperative neurophysiological monitoring: technical note.

Intraoperative neurophysiological mapping and monitoring of eloquent brain areas can be combined with image-guided localisation to enhance the safety and efficacy of surgical procedures in the motor cortex. We designed a new type of cortical electrode which can be repeatedly placed on the cortical surface and allows accurate and reproducible stimulation by means of a navigation pointer. The newly designed device consists of a monopolar electrode contact for direct cortical stimulation, housed in a holder which allows placement, easy removal, and precise repeated placement of a surgical navigation pointer. It can be used for navigation-guided, high-frequency anodal monopolar cortical stimulation (MCS) for the mapping of eloquent cortex, and for monitoring of motor pathways. While the cortex is stimulated, compound muscle action potentials (CMAP) are recorded from muscles of the contralateral extremities and are assessed both qualitatively and quantitatively. When the device is used in combination with intraoperative navigation, the stimulation sites may optionally be registered or displayed on the system monitor. This allows repeated pinpointing and obviates the need for strip or grid electrodes in the operative field; although such electrodes may be useful for continuous monitoring, they often are in the surgeon's way. In addition, the primary and supplementary motor cortex can be mapped by determining the location of the sites of stimulation on surface-projected images of the cerebral cortex.

Brain Mapping↗
PubMed2000

Accurate placement of the distal end of a ventriculoatrial shunt catheter using Alphacard: direct intraoperative comparison with fluoroscopy.

BACKGROUND: Surgical insertion of a ventriculoatrial shunt requires accurate placement of the atrial catheter in the right atrium in order to prevent postoperative complications. Fluoroscopy is the standard method for monitoring correct positioning of the catheter. METHODS: This paper reports a prospective study in 50 patients with the aim of comparing electrocardiographic monitoring of the catheter position by means of Alphacard with concomitant intraoperative fluoroscopic examination. The Alphacard was evaluated in terms of accuracy, time requirement, and ease of handling. The mean postoperative follow-up period was 54 (range 42-66) months. FINDINGS: Reliable control of the catheter position was possible by means of electrocardiographic guidance in all 50 patients (100%) by fluoroscopy in 49 cases (98%). The average time required for intra-operative monitoring of the catheter position was 55 (40-70) seconds for electrocardiography as compared to 8 (5-12) minutes for fluoroscopy. None of the patients showed obstruction of the atrial catheter during the postoperative follow-up period. INTERPRETATION: Alphacard offers an excellent alternative for monitoring the position of the tip of an atrial catheter because it requires little equipment and time. In terms of reliability, it is comparable or even superior to fluoroscopy.

Adolescent↗
PubMed2000

Animal model for cerebral arteriovenous malformation.

BACKGROUND: The present study was conducted to establish an animal model for the investigation of the pathophysiology and haemodynamics of cerebral arteriovenous malformation (AVM) but also to assess therapeutic aspects. METHOD: For anatomic and haemodynamic reasons, dogs were chosen as the animal model. An arteriovenous fistula was created by interposing a segment of the superficial temporal artery between one of the main branches of the middle cerebral artery and the dorsal sagittal sinus. A temporal muscle graft supplied by this artery was implanted intracerebrally in the ischaemic area. FINDINGS: The angiographic and histopathologic findings obtained in the animal model are comparable with the situation found in intracerebral AVM in humans. INTERPRETATION: The animal model of intracerebral AVM established in this study allows for further investigation of the pathophysiology and dynamics of this disorder. It may help to develop better therapeutic options and thus improve the prognosis of affected patients.

Animals↗
PubMed2000

Permanent postoperative anosmia: a serious complication of neurovascular decompression in the sitting position.

In posterior fossa surgery, the sitting position offers a number of advantages believed to outweigh complications such as air embolism and pneumatocephalus. For this reason, the sitting position is frequently used in neurovascular decompression for trigeminal neuralgia. Two years ago we reported on a previously undescribed complication: permanent postoperative anosmia. Following the recent occurrence of a second case, we conducted a nationwide survey to determine the frequency of this complication. Permanent postoperative anosmia following surgical procedures in the sitting position has been observed in 3 other institutions. In addition, the survey revealed that only 40% of German neurosurgeons still favor the sitting position for surgery of the posterior cranial fossa. Considering that permanent anosmia severely reduces quality of life, and that it can be avoided by using another position, the sitting position for surgical procedures in the posterior fossa should be restricted to special cases (e.g., brain stem tumors).

Decompression, Surgical↗
PubMed2000

Surgical treatment of spinal hemangioblastomas.

BACKGROUND: The routine use of magnetic resonance imaging (MRI) in recent years for the diagnostic assessment of the spinal column and especially for screening patients with von Hippel-Lindau (vHL) disease has shown that spinal hemangioblastomas (sHBs) are more common than assumed so far. Since most sHBs are thus discovered while they are still asymptomatic, especially in vHL disease, the question arises whether and when these tumors should be treated. The present article reports the results of the surgical treatment of sHBs using the protocol described below and compares them to the course in a control group of patients with conservatively treated sHBs. PATIENTS AND METHODS: A total of 30 sHBs were treated microsurgically in 15 patients. Hemangioblastoma-associated cysts were merely opened in 14 cases, drained with the help of Teflon cotton in 2 of these cases, and not opened in 4 instances. Laminoplasties were performed with insertion of absorbable, MRI-compatible microosteosynthesis plates. Perioperatively, all patients were administered methylprednisolone according to the NASCIS (National Acute Spinal Cord Injury Study) scheme, and sensory evoked potentials were monitored intra-operatively in all cases. Nine patients in whom the course of primarily conservative treatment of a total of 17 asymptomatic sHBs was documented served as controls. The follow-up time was 7 to 51 months (mean 20) after surgery and 10 to 51 months (mean 21) in the control group. FINDINGS: Preoperative HB-associated pareses showed transient postoperative deterioration (n = 5). The other accompanying neurological deficits improved in 6 HBs and remained unchanged in all other HBs (n = 19), of which 16 had been asymptomatic before surgery. In the control group, 6 HBs (in 6 different patients) became permanently symptomatic despite subsequent surgical treatment according to the study protocol. INTERPRETATIONS: With the new diagnostic tools now available, microsurgical removal of spinal hemangioblastomas has a low morbidity rate, suggesting that surgical treatment should be considered even for asymptomatic sHBs in certain circumstances.

Adolescent↗
PubMed2000

Methylcitrate synthase from Aspergillus nidulans: implications for propionate as an antifungal agent.

Aspergillus nidulans was used as a model organism to investigate the fungal propionate metabolism and the mechanism of growth inhibition by propionate. The fungus is able to grow slowly on propionate as sole carbon and energy source. Propionate is oxidized to pyruvate via the methylcitrate cycle. The key enzyme methylcitrate synthase was purified and the corresponding gene mcsA, which contains two introns, was cloned, sequenced and overexpressed in A. nidulans. The derived amino acid sequence of the enzyme shows more than 50% identity to those of most eukaryotic citrate synthases, but only 14% identity to the sequence of the recently detected bacterial methylcitrate synthase from Escherichia coli. A mcsA deletion strain was unable to grow on propionate. The inhibitory growth effect of propionate on glucose medium was enhanced in this strain, which led to the assumption that trapping of the available CoA as propionyl-CoA and/or the accumulating propionyl-CoA itself interferes with other biosynthetic pathways such as fatty acid and polyketide syntheses. In the wild-type strain, however, the predominant inhibitor may be methylcitrate. Propionate (100 mM) not only impaired hyphal growth of A. nidulans but also synthesis of the green polyketide-derived pigment of the conidia, whereas in the mutant pigmentation was abolished with 20 mM propionate.

Amino Acid Sequence↗
PubMed2000

Subdural air limits the elicitation of compound muscle action potentials by high-frequency transcranial electrical stimulation.

High-frequency transcranial electrical stimulation was performed in 8 patients undergoing surgery in the sitting position. Following the opening of the dura of the posterior fossa changes in compound muscle action potentials were observed. These changes were not attributable to surgical manoeuvres at the brain stem or spinal cord, or to anaesthetic changes. In all these cases intraoperative fluoroscopy of the skull revealed a subdural air collection underneath the stimulation electrodes. Such a subdural air collection, not infrequent in patients operated on in the sitting position, limits the application of high-frequency transcranial electrical stimulation as a monitoring technique. It remains unclear if this effect is due to the increasing distance between scalp and cortex and the insulating effect of subdural air, or due to displacement of the motor cortex. The practical importance of this report is derived from the increasing application of intraoperative motor pathway monitoring.

Adult↗
PubMed2000

Transcranial Doppler ultrasonography as a screening technique for detection of a patent foramen ovale before surgery in the sitting position.

BACKGROUND: Venous air embolism has been reported to occur in 23-45% of patients undergoing neurosurgical procedures in the sitting position. If venous air embolism occurs, a patent foramen ovale (PFO) is a risk factor for paradoxical air embolism and its sequelae. Preoperative screening for a PFO is therefore recommended by some investigators. The reference standard for identifying a PFO is contrast-enhanced transesophageal echocardiography (c-TEE). Contrast-enhanced transcranial Doppler ultrasonography (c-TCD) and contrast-enhanced transthoracic echocardiography (c-TTE) are noninvasive alternative methods, but so far there are no studies as to their diagnostic validity in neurosurgical patients. METHODS: The sensitivity and specificity of c-TCD and c-TTE in detecting a PFO were determined in a prospective study using c-TEE as the reference standard. Preoperative c-TCD, c-TTE, and c-TEE studies were performed during the Valsalva maneuver after intravenous echo-contrast medium (D-Galactose, Echovist-300, Schering AG, Berlin, Germany) was administered in 92 consecutive candidates (47 men and 45 women; mean age, 51 yr; range, 25-72 yr) before neurosurgical procedures in the sitting position. RESULTS: A PFO was detected in 24 of the 92 patients (26.0%) using c-TEE. c-TCD correctly identified 22 patients, whereas c-TTE only correctly identified 10. This corresponds to a sensitivity of 0.92 for c-TCD and 0.42 for c-TTE. The negative predictive value was 0.97 for c-TCD compared with 0.83 for c-TTE. The prevalence of a PFO in patients with a posterior fossa lesion was 27%, and in the group with cervical disc herniation was 24% as detected by c-TEE. The incidence of intraoperative venous air embolism was 35% in cases of cervical foraminotomy and 75% in posterior fossa surgery as detected by c-TEE. CONCLUSIONS: c-TCD is a highly sensitive and highly specific method for detecting a PFO. Because c-TCD is noninvasive, it may be more suitable than c-TEE for routine preoperative screening for a PFO. C-TTE is not reliable in detecting a PFO.

Adult↗
PubMed2000

Factors associated with intracranial hemorrhage in cases of cerebral arteriovenous malformation.

OBJECTIVE: The standard categorization of arteriovenous malformations (AVMs) involves the Spetzler-Martin grading system, which uses a simple analysis of size, location (superficial or deep), and the presence of deep or superficial drainage. Hemodynamic risk factors are also thought to play important roles in the pathogenesis of these lesions and to be associated with the intracranial hemorrhage (ICH) rate. The actual hemodynamic factors for AVMs cannot be easily measured, but angioarchitectural features can be assessed and used as surrogate parameters. METHODS: The AVM angioarchitectural features for 662 patients were analyzed, and their associations with ICH as a presenting sign were studied. A cross-sectional analysis was used to qualify the strength of associations among clinical features, angioarchitectural characteristics, and ICH before treatment. RESULTS: The multivariate analysis indicated that arterial stenosis and arterial ectasia were associated with lower ICH rates, whereas venous stenosis increased the rate of ICH. The presence of angiogenesis modified the effects of arterial and venous stenosis. Furthermore, the effect of venous stenosis depended on the location of the nidus. The presented data do not support a direct positive association between associated aneurysms and ICH. CONCLUSION: Certain angiographic features seem to have prognostic potential with respect to the occurrence of ICH among patients with AVMs. A discriminatory prognostic index is proposed; its relevance must be proven in a future prospective study.

Adolescent↗
PubMed2000

Cerebral arteriovenous malformations and associated aneurysms: analysis of 305 cases from a series of 662 patients.

OBJECTIVE: Spontaneous intracranial hemorrhage is the primary danger for patients with cerebral arteriovenous malformations (AVMs). Associated aneurysms are considered weak points that increase the risk of intracranial hemorrhage. Aneurysms are classified as proximal aneurysms (PROXs) or intranidal aneurysms (INs). METHODS: The present study was based on a series of 662 patients who presented with AVMs between 1985 and 1995. Its purpose was to evaluate prestated hypotheses using prospectively collected data. In 305 of these 662 patients, 372 INs and 313 PROXs were observed and analyzed with respect to their shapes, locations, and sizes. Partial targeted endovascular treatment with n-butylcyanoacrylate was performed for 450 of the 662 patients (68%) in this series, using a standard protocol. Of 450 treated patients, 181 (40%) had at least one IN and 138 (30.7%) had at least one PROX. Analysis of changes in the sizes of PROXs was based on the follow-up data for 83 treated patients, with a total of 149 PROXs. Changes in the sizes of PROXs in treated patients were analyzed with respect to PROX shapes, PROX locations, and treated AVM occlusion rates. Univariate and multivariate event data analyses were used to study factors influencing aneurysm shrinkage. False aneurysms were excluded from the series. RESULTS: Presentation with intracranial hemorrhage was not correlated with any type of aneurysm. However, INs demonstrated a higher rebleeding rate (P < 0.002) before treatment. Among 181 patients, 92.2% of INs were occluded, together with the related portions of the AVM nidi. In cases of PROXs, embolization of the cerebral AVM compartment fed by the artery with the aneurysm was a priority. During follow-up monitoring of 83 treated patients with 149 PROXs, 100% shrinkage was observed for 12 PROXs and more than 50% shrinkage was observed for 33 PROXs. The median time required for more than 50% shrinkage was 3.5 years. The shrinkage of PROXs was influenced by the degree of AVM occlusion (P = 0.027) and occurred faster for PROXs on midline structures, such as the anterior cerebral artery and the circle of Willis, compared with arteries distal to the circle of Willis (P = 0.004). No rupture of untreated PROXs was observed after partial targeted treatment of AVMs. CONCLUSION: PROXs are not primary treatment targets, compared with AVMs themselves. INs should be primary targets of endovascular therapy, because of their increased risk of rebleeding.

Adolescent↗
PubMed2000

Intraoperative microvascular Doppler ultrasonography in cerebral aneurysm surgery.

OBJECTIVES: Outcome of surgical treatment of cerebral aneurysms may be severely compromised by local cerebral ischaemia or infarction resulting from the inadvertent occlusion of an adjacent vessel by the aneurysm clip, or by incomplete aneurysm closure. It is therefore mandatory to optimise clip placement in situ to reduce the complication rate. The present study was performed to investigate the reliability of intraoperative microvascular Doppler ultrasonography (MDU) in cerebral aneurysm surgery, and to assess the impact of this method on the surgical procedure itself. METHODS: Seventy five patients (19 men, 56 women, mean age 54.8 years, range 22-84 years) with 90 saccular cerebral aneurysms were evaluated. Blood flow velocities in the aneurysmal sac and in the adjacent vessels were determined by MDU before and after aneurysm clipping. The findings of MDU were analysed and compared with those of visual inspection of the surgical site and of postoperative angiography. Analysis was also made of the cases in which the clip was repositioned due to MDU findings. RESULTS: A relevant stenosis of an adjacent vessel induced by clip positioning that had escaped detection by visual inspection was identified by Doppler ultrasonography in 17 out of 90 (18.9%) aneurysms. In addition, Doppler ultrasound demonstrated a primarily unoccluded aneurysm in 11 out of 90 (12.2%) patients. The aneurysm clip was repositioned on the basis of the MDU findings in 26 out of 90 (28.8%) cases. In middle cerebral artery (MCA) aneurysms, the MDU results were relevant to the surgical procedure in 17 out of 44 (38.6%) cases. Whereas with aneurysms of the anterior cerebral artery significant findings occurred in only five of 32 cases (15.6%; p<0.05). The clip was repositioned on the basis of the MDU results in 18 out of 50 (36%) aneurysms in patients with subarachnoid haemorrhage (SAH) grade I-V compared with only eight out of 40 (20%) aneurysms in patients without SAH (p<0.05). CONCLUSIONS: MDU should be used routinely in cerebral aneurysm surgery, especially in cases of MCA aneurysms and after SAH. Present data show that a postoperative angiography becomes superfluous whenever there is good visualisation of the "working site" and MDU findings are clear.

Adult↗
PubMed2000

Can continuous intraoperative facial electromyography predict facial nerve function following cerebellopontine angle surgery?

Intraoperative cranial nerve monitoring has significantly improved the preservation of facial nerve function following surgery in the cerebellopontine angle (CPA). Facial electromyography (EMG) was performed in 60 patients during CPA surgery. Pairs of needle electrodes were placed subdermally in the orbicularis oris and orbicularis oculi muscles. The duration of facial EMG activity was noted. Facial EMG potentials occurring in response to mechanical or metabolic irritation of the corresponding nerve were made audible by a loudspeaker. Immediate (4-7 days after tumor excision) and late (6 months after surgery) facial nerve function was assessed on a modified House-Brackmann scale. Late facial nerve function was good (House-Brackmann 1-2) in 29 of 60 patients, fair (House-Brackmann 3-4) in 14, and poor (House-Brackmann 5-6) in 17. Postmanipulation facial EMG activity exceeding 5 minutes in 15 patients was associated with poor late function in five, fair function in six, and good function in four cases. Postmanipulation facial EMG activity of 2-5 minutes in 30 patients was associated with good late facial nerve function in 20, fair in eight, and poor in two. The loss of facial EMG activity observed in 10 patients was always followed by poor function. Facial nerve function was preserved postoperatively in all five patients in whom facial EMG activity lasted less than 2 minutes. Facial EMG is a sensitive method for identifying the facial nerve during surgery in the CPA. EMG bursts are a very reliable indicator of intraoperative facial nerve manipulation, but the duration of these bursts do not necessarily correlate with short- or long-term facial nerve function despite the fact that burst duration reflects the severity of mechanical aggression to the facial nerve.

Cranial Fossa, Posterior↗
PubMed1999

Demonstration of cerebral plasticity by intra-operative neurophysiological monitoring: report of an uncommon case.

It has been postulated long ago that "eloquent" areas shift their location in patients with arteriovenous malformations (AVM). Obviously the "motor region" in not located in the precentral gyrus in a patient with an AVM in the "motor region". We report on the case of a 15-year old boy with an AVM in the left sensorimotor cortex, in whom intra-operative mapping showed an inexcitability of the precentral gyrus, while stimulation of the cortex anterior to the primary motor cortex elicited motor responses. This indicates that motor function was translocated from the primary to the supplementary motor cortex. Surgery was performed under general anaesthesia. Neurophysiological monitoring was performed throughout surgery. The central sulcus was identified by phase reversal of the somatosensory evoked potentials. The motor cortex was mapped by direct high-frequency (500 Hz) monopolar anodal stimulation. In the patient herein reported, stimulation of the "anatomically" defined primary motor cortex induced no motor response, as expected. Motor response was elicited only by stimulation of the cortex anterior to the precentral gyrus. There was no postoperative deterioration of motor function. These observations indicate that the precentral gyrus was functionally "useless". The motor region was relocated into more rostral areas in the supplementary motor cortex. This translocation of function in the presence of an AVM indicates cerebral plasticity.

Adolescent↗
PubMed1999

Comparison between monopolar and bipolar electrical stimulation of the motor cortex.

Intra-operative neurophysiological techniques allow reliable identification of the sensorimotor region and make their anatomical and functional preservation feasible. Monopolar cortical stimulation has recently been described as a new mapping technique. In the present study this method was compared to the "traditional" technique of bipolar stimulation. Functional mapping of the motor cortex was performed in 35 patients during surgery in the central region. The central sulcus (CS) was identified by somatosensory evoked potential (SEP) phase reversal. Cortical motor mapping was first performed by monopolar anodal stimulation with a train of 500 Hz (7-10 pulses) followed by bipolar stimulation (pulses at 60 Hz with max. 4 sec train duration). Surgery was performed under general anaesthesia without muscle relaxants. Of 280 motor responses elicited by bipolar cortical stimulation, 54.23% [152] were located in the primary motor cortex (PMC), 37.85% 106[ outside the motor strip in the secondary motor cortex (SMC), and 8% 22[ posterior to the CS. Of 175 motor responses elicited by monopolar cortical stimulation. 68.57% 120[ were located in the SMC, 23.42% 41[ in the SMC and 8% 14[ posterior to the CS. Contrary to the general clinical view, there is considerable overlapping of primary motor units over a cortical area much broader than the "classical" narrow motor strip along the CS. Bipolar cortical stimulation is more sensitive than monopolar for mapping motor function in the premotor frontal cortex. Both methods are equally sensitive for mapping the primary motor cortex.

Adolescent↗
PubMed1999

Brain tumor surgery in geriatric patients: a critical analysis in 44 patients over 80 years.

BACKGROUND: The decision of whether to operate on brain tumors in elderly patients has not been made easier despite diagnostic and therapeutic advances facilitating their diagnosis. Little is known about the outcome of brain tumor surgery in patients 80 years or older probably because the number of these patients, although increasing, is still small. METHODS: The results of brain tumor surgery in 44 patients aged 80-86 years (mean age 83 years) were analyzed to determine which factors are relevant in the evaluation of the operative risk. The following parameters were analyzed with regard to the outcome: tumor volume, location, histopathology, preoperative condition, and concomitant diseases. RESULTS: At discharge 19 patients (43%) had improved while 14 (32%) remained unchanged. Nevertheless, the overall results were unsatisfactory in 10 patients (23%), of whom 5 died in hospital. Tumor location, volume, and histopathology did not correlate with the outcome. The preoperative cerebrovascular condition and the existence of multiple concomitant diseases were clearly the determining factors for the outcome. CONCLUSIONS: These results indicate that patients with life-threatening tumors or those causing persistent and intolerable brain dysfunction suffering from symptomatic cerebrovascular atherosclerosis as well as from multiple treatment requiring concomitant diseases did definitely not benefit from surgery.

Aged↗
PubMed1999

Rupture of several parasagittal bridging veins without subdural bleeding.

This case reports on a fatal craniocerebral trauma involving numerous ruptured cerebral bridging veins that did not bleed subdurally, despite approximately 15 hours of survival. A 15-year-old girl was severely injured as the passenger of a car that crashed sideways into a tree. She-suffered a cerebral trauma of the "diffuse injury" type and was unconscious after the accident. Her computed tomographic scan at admission showed massive brain edema, axial herniation, and marked hypodensity of the bilateral carotid flow area. Despite intensive care measures, the clinical course was characterized by central decompensation with therapy-resistant cardiocirculatory insufficiency. The autopsy revealed ruptures of numerous parasagittal bridging veins. The injured vessels were not thrombosed, and yet there was absolutely no subdural bleeding. This unusual combination of findings is assumed to be caused by an isolated collapse of cerebral circulation occurring shortly after the accident and primarily attributed to a rapid increase of intracranial pressure.

Accidents, Traffic↗