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Biomedical subjects

J Zentner

Publications and source records attributed to J Zentner.

At least 55 records · Page 3Linked to original sources
PubMed1998

Isoflurane plus nitrous oxide versus propofol for recording of motor evoked potentials after high frequency repetitive electrical stimulation.

The goal of this study was to test the influence of two widespread techniques of general anesthesia on motor evoked potentials (MEP) in response to transcranial and direct cortical high frequency repetitive electrical stimulation. Total intravenous anesthesia (TIVA) based on propofol and alfentanil was examined in 17 patients (group A), and balanced anesthesia (BA), based on nitrous oxide, isoflurane and fentanyl, was studied in 13 patients (group B). Distinct motor responses were available in 15 of 17 patients (88%) of group A, and in one of 13 patients (8%) of group B. Amplitudes increased significantly with increasing stimulus intensity and number of pulses under conditions of TIVA. At the same time, latencies decreased significantly with increasing stimulus intensity and decreasing interstimulus interval, but not with increasing number of pulses. It is hypothesized that propofol suppresses corticospinal I-waves at the cortical level, resulting in a conduction block at the level of the alpha-motoneuron, and that this effect may be overcome by high frequency repetitive stimulation. In contrast, nitrous oxide and isoflurane seem to have an additional suppressive effect on corticospinal D-waves, which may be overcome by higher stimulation intensity. In conclusion, transcranial high frequency repetitive stimulation and TIVA provide a feasible setting for intraoperative MEP monitoring, while higher doses of nitrous oxide and isoflurane are not compatible with recording of muscular activity elicited by the stimulation technique as described.

Adolescent↗
PubMed1997

Influence of nitrous oxide on motor-evoked potentials.

STUDY DESIGN: Rabbits were used as an experimental model in the study of motor-evoked potentials. OBJECTIVES: To evaluate the effect of nitrous oxide on motor-evoked potentials while monitoring direct muscle and spinal cord responses. SUMMARY OF BACKGROUND DATA: Motor-evoked potential monitoring provides a promising tool for intraoperative assessment of descending pathways function. However, to date, this technique is still at an experimental stage, since its routine use is mainly limited because of intraoperative recording difficulties caused by the influence of anesthesia. METHODS: Eight male rabbits weighing between 3000 g and 3500 g were studied. Motor-evoked potentials were recorded from the extremity muscles and from the epidural space of the thoracic cord in response to electrical stimulation of the motor cortex at baseline conditions and at increasing nitrous oxide concentrations (10-70 vol%). RESULTS: The authors found a major suppressive effect of high nitrous oxide concentrations on the electromyographic responses. With 50 vol% nitrous oxide, electromyographic amplitudes were suppressed to 46% (fore leg) and 14% (hind leg) of the baseline values, whereas latencies did not change significantly. In contrast to muscular activity, spinal evoked responses representing neural activity were not affected by any concentration of nitrous oxide. CONCLUSIONS: Intraoperative monitoring of descending pathways by means of motor-evoked potentials during anesthesia of the rabbits based on nitrous oxide is feasible when neural activity is evaluated. Higher doses of nitrous oxide, however, are not compatible with recording of muscular activity.

Anesthetics, Inhalation↗
PubMed1997

Surgical management of brain-stem cavernomas.

We present a series of seven patients who were operated on for symptomatic brain-stem cavernomas. The following approaches were used: medial suboccipital (N = 4), lateral suboccipital (N = 1), subtemporal-transtentorial (N = 1), and frontal transcortical-transventricular-subchorioidal-trans velum interpositum (N = 1). Intraoperative motor (N = 4) and somatosensory (N = 1) evoked potential monitoring revealed temporary changes in 3 patients. Immediately postoperatively, the following additional deficits were observed in 6 patients: oculomotor nerve paresis (N = 2), abducens nerve paresis (N = 3), facial nerve paresis (N = 2), deafness (N = 1), and increased ataxia (N = 3). One patient died due to septic complications not related to surgery. After a mean observation time of 2 years, 2 patients had improved, 3 were unchanged, and 1 patient deteriorated as compared to his preoperative status. In conclusion, surgical treatment of brain-stem cavernomas, although carrying a significant risk of temporary neurological deterioration is recommended in symptomatic patients in whom the cavernoma seems to reach the surface of the brain-stem. Intraoperative functional topographic mapping and monitoring have proven useful tools lowering the surgical risks in these patients.

Adult↗
PubMed1997

Diagnosis and treatment of frontobasal skull fractures.

During a five-year-period (January 1990 to December 1994) a total of 67 patients were operated on for frontobasal skull fractures. The indication for surgical treatment was based on the evidence of fractures encroaching paranasal sinuses or the cribriform plate on high-resolution axial or coronal CT scans. The following clinical signs indicating frontobasal trauma were observed: 25 patients (37%) showed rhinoliquorrhea, 14 (21%) had raccoon's eyes, and 2 (3%) had meningitis. Distinct dura laceration was observed intraoperatively in 64 of 67 patients (96%). In our experience, high resolution CT has proven to be a sensitive diagnostic tool for frontobasal skull fractures. With respect to the high coincidence of fractures and dura lacerations, the indication for surgical treatment based on CT findings seems to be justified.

Adolescent↗
PubMed1997

Effects of selective h5-HT1B (SB-216641) and h5-HT1D (BRL-15572) receptor ligands on guinea-pig and human 5-HT auto- and heteroreceptors.

Human cerebral cortical slices and synaptosomes, guinea-pig cerebral cortical slices and human right atrial appendages were used to study the effects of SB-216641, a preferential h5-HT1B receptor ligand, and of BRL-15572, a preferential h5-HT1D receptor ligand, on the presynaptic h5-HT1B and h5-HT1B-like autoreceptors in the human and guinea-pig brain preparations, respectively, and on the presynaptic h5-HT1D heteroreceptors in the human atrium. The brain preparations, preincubated with [3H]serotonin ([3H]5-HT), and the segments of atrial appendages, preincubated with [3H]noradrenaline, were superfused with modified Krebs' solution and tritium overflow was evoked electrically (human and guinea-pig cerebral cortex slices and human atrial appendages) or by high K+ (human cerebral cortex synaptosomes). The electrically evoked tritium overflow from guinea-pig cerebral cortex slices was reduced by the 5-HT receptor agonist 5-carboxamidotryptamine (5-CT). This effect was not modified by BRL-15572 (2 microM; concentration 154 times higher than its Ki at h5-HT1D receptors) but was antagonized by SB-216641 (0.1 microM; concentration 100 times higher than its Ki at h5-HT1B receptors; apparent pA2 8.45). SB-216641 (0.1 microM) by itself facilitated, whereas BRL-15572 (2 microM) did not affect, the evoked overflow. In human cerebral cortex slices SB-216641 (0.1 microM) also facilitated, and BRL-15572 (2 microM) again failed to affect, the electrically evoked tritium overflow. In human cerebral cortical synaptosomes, 5-CT reduced the K+-evoked tritium overflow. This response was unaffected by BRL-15572 (300 nM) but antagonized by SB-216641 (15 nM; drug concentrations 23 and 15 times higher than their Ki at h5-HT1D and h5-HT1B receptors, respectively). Both drugs, given alone, did not modify the K+-evoked tritium overflow. In human atrial appendages, the electrically evoked tritium overflow was inhibited by 5-HT in a manner susceptible to antagonism by BRL-15572 (300 nM; 23 times Ki at h5-HT1D receptors) but not by SB-216641 (30 nM; 30 times Ki at h5-HT1B receptors). Both drugs by themselves did not change the electrically evoked tritium overflow. In conclusion, SB-216641 behaves as a preferential antagonist at native human 5-HT1B receptors and BRL-15572 as a preferential antagonist at native human 5-HT1D receptors. These compounds are clearly useful tools for the differentiation between human 5-HT1B and 5-HT1D receptors in functional studies.

Animals↗
PubMed1997

Cannabinoid CB1 receptor-mediated inhibition of noradrenaline release in the human and guinea-pig hippocampus.

We examined the question of whether cannabinoid receptors modulating noradrenaline release are detectable in the brain of humans and experimental animals. For this purpose, hippocampal slices from humans, guinea-pigs, rats and mice and cerebellar, cerebrocortical and hypothalamic slices from guinea-pigs were incubated with [3H]noradrenaline and then superfused. Tritium overflow was evoked either electrically (0.3 or 1 Hz) or by introduction of Ca2+ ions (1.3 mM) [corrected] into Ca(2+)-free, K(+)-rich medium (25 mM) [corrected] containing tetrodotoxin 1 microM. Furthermore, the cAMP accumulation stimulated by forskolin 10 microM was determined in guinea-pig hippocampal membranes. We used the following drugs: the cannabinoid receptor agonists (-)-cis-3-[2-hydroxy-4-(1,1- dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclo-hexanol (CP-55,940) and R(+)-[2,3-dihydro-5-methyl-3- [(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]- (1-naphthalenyl)methanone (WIN 55,212-2), the inactive S(-)-enantiomer of the latter (WIN 55,212-3) and the CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)- 1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide (SR 141716). The electrically evoked tritium overflow from guinea-pig hippocampal slices was reduced by WIN 55,212-2 (pIC30% 6.5) but not affected by WIN 55,212-3 up to 10 microM. The concentration-response curve of WIN 55,212-2 was shifted to the right by SR 141716 (0.032-microM) (apparent pA2 8.2), which by itself did not affect the evoked overflow. WIN 55,212-2 1 microM also inhibited the Ca(2+)-evoked tritium overflow in guinea-pig hippocampal slices and the electrically evoked overflow in guinea-pig cerebellar, cerebrocortical and hypothalamic slices as well as in human hippocampal slices but not in rat and mouse hippocampal slices. SR 141716 (0.32 microM) markedly attenuated the WIN 55,212-2-induced inhibition in guinea-pig and human brain slices. SR 141716 0.32 microM by itself increased the electrically evoked tritium overflow in guinea-pig hippocampal slices but failed to do so in slices from the other brain regions of the guinea-pig and in human hippocampal slices but failed to do so in slices from the other brain regions of the guinea-pig and in human hippocampal slices. The cAMP accumulation stimulated by forskolin was reduced by CP-55,940 and WIN 55,212-2. The concentration-response curve of CP 55,940 was shifted to the right by SR 141716 (0.1 microM; apparent pA2 8.3), which by itself did not affect cAMP accumulation. In conclusion, cannabinoid receptors of the CB1 subtype occur in the human hippocampus, where they may contribute to the psychotropic effects of cannabis, and in the guinea-pig hippocampus, cerebellum, cerebral cortex and hypothalamus. The CB1 receptor in the guinea-pig hippocampus is located presynaptically, is activated by endogenous cannabinoids and may be negatively coupled to adenylyl cyclase.

Animals↗
PubMed1997

Sarcoidosis presenting as an intra- or extra-axial cranial mass: report of two cases.

Sarcoidosis may also present as an extra- or intra-axial mass involving the central nervous system. These lesions are sometimes operated upon, because a neoplasm is suspected. We report two cases of unusual tumour-like extra- and intra-axial sarcoidosis. The extra-axial mass was just medial to the jugular foramen. Its morphology and signal characteristics differed from the more common lesions in this area. The intra-axial mass was in the temporal lobe, with only minor leptomeningeal involvement. Extra-axial sarcoidosis can be confused with a meningioma because these lesions can give relatively low signal on T2-weighted images. Intra-axial masses are presumed to represent a propagation and fusion of multiple leptomeningeal granulomas through the Virchow-Robin spaces in the brain; this pattern can be sought on contrast-enhanced T1-weighted images.

Aged↗
PubMed1997

Neuronal loss and gliosis of the amygdaloid nucleus in temporal lobe epilepsy. A quantitative analysis of 70 surgical specimens.

Although clinical and electrophysiological evidence indicates that the amygdaloid body plays an important role in the pathogenesis of temporal lobe epilepsy, there are very few detailed data on histopathological changes in this nucleus in epilepsy patients. In the present study we have examined the lateral nucleus of the amygdaloid body in 70 surgical specimens from patients with temporal lobe epilepsy and in 10 control specimens with respect to neuronal density and gliosis. The results were compared to the neuronal loss in the hippocampal formation. Our goal was to examine the pathological alterations of the amygdaloid body and their correlation with other morphological changes in temporal lobe epilepsy. In epilepsy patients with Ammon's horn sclerosis or focal lesions of the temporal lobe, the neuronal density of the lateral amygdaloid nucleus was significantly decreased as compared to normal controls (P < 0.001). Overall, the mean volumetric density in epilepsy patients was reduced to 59% of that in normal individuals. There was no correlation between the neuronal density in the lateral amygdaloid nucleus and that in the different segments of the hippocampal formation or to the age at onset or the duration of epilepsy. The neuronal loss of the amygdaloid nucleus correlated well with the presence of fibrillary gliosis. Our findings demonstrate that the amygdaloid body is severely altered in most patients with temporal lobe epilepsy and that these changes are independent of those in the hippocampus. The presence of neuronal loss and gliosis in the amygdaloid nucleus of patients with focal lesions but no Ammon's horn sclerosis is compatible with an involvement of the amygdala in secondary epileptogenesis.

Adolescent↗
PubMed1997

Surgical and neurological complications in a series of 708 epilepsy surgery procedures.

OBJECTIVE: There are few modern data on the complications of surgery for epilepsy from the neurosurgeon's point of view. A survey of complications observed in a large current epilepsy surgery series is presented to facilitate the assessment of a risk:benefit ratio, which must be known when planning for epilepsy surgery and counseling patients. METHODS: A series of 429 consecutive patients operated on during 6.5 years in the newly established University of Bonn epilepsy surgery program was, in part, retrospectively, and, in larger part, prospectively analyzed for complications originating from 279 invasive diagnostic procedures and 429 therapeutic procedures. Neuropsychological and psychiatric complications as well as the rate of failure to control seizures are not addressed in this article. RESULTS: Two hundred and seventy-nine temporal operations, 59 frontal operations, 22 other extratemporal operations, 33 callosotomies, 3 multilobectomies, and 33 hemispherectomies were performed. Complications were grouped into general surgical and neurological complications. No mortality resulted from 708 invasive procedures. Two hundred and seventy-nine invasive diagnostic procedures (various combinations of strip, grid, and depth electrode insertions) resulted in 3.6% transient morbidity (2.9% surgical complications, 0.7% neurological complications) and 0.7% permanent morbidity (dysphasia). During 429 therapeutic procedures, 33 surgical complications were encountered. None of these resulted in permanent morbidity, except for the necessity for permanent shunt insertion in three patients. Wound infection was the most frequent surgical complication, but we were able to demonstrate a steady decrease during the 6.5-year observation period. The total rate of neurological complications in 429 therapeutic procedures was 5.4%, with 3.03% causing transient morbidity and 2.33% causing permanent morbidity. CONCLUSION: Our data indicate that epilepsy surgery can be performed with an acceptable rate of resultant morbidity. The indications for epilepsy surgery, the learning curve determined, and the results from other series are discussed in the light of these figures.

Adolescent↗
PubMed1997

Surgical treatment of neoplasms associated with medically intractable epilepsy.

OBJECTIVE: Surgical treatment in patients with brain tumors and medically intractable epilepsy is aimed at the removal of the neoplasm and complete seizure control. However, an adequate surgical approach is still controversial. This study was designed to analyze the factors for the optimum surgical treatment of these patients. METHODS: The clinical, electrophysiological, operative, and histopathological data of 146 consecutive patients who underwent surgery between November 1987 and May 1995 for intrinsic brain tumors and pharmacoresistant epilepsy were evaluated. RESULTS: The majority of the tumors were located in the temporal lobe (n = 116) and involved the cortical gray matter. The most frequent tumors were gangliogliomas (n = 65), pilocytic astrocytomas (n = 21), and dysembryoplastic neuroepithelial tumors (n = 19). All but three tumors (98%) were of low histopathological grade (World Health Organization Grades I or II). The biological behavior of the tumors was strikingly indolent, as indicated by a long preoperative history of chronic seizures (mean, 14 yr). In all cases, complete resection of the tumor, including the epileptogenic area (as determined by noninvasive and/or invasive recordings of the zone of seizure onset and persistent interictal activity), was intended. Complications were encountered in 11 cases (8%). However, no patient died and there was no permanent morbidity. Of the 124 patients who had postoperative follow-up examinations more than 6 months after resection, 71% were seizure-free, 11% had no more than two seizures per year, 13% showed a reduction of seizure frequency of at least 75%, and 5% had no appreciable reduction in seizure frequency. CONCLUSION: The data indicate that neoplasms associated with medically intractable epilepsy constitute a distinct clinicopathological group of tumors that arise in young hosts, involve the cortex, and exhibit indolent biological behavior for many years. Complete surgical removal of these tumors, including the epileptogenic area, can achieve excellent seizure control.

Adolescent↗
PubMed1997

Multiple subpial transection for control of epileptic seizures: effectiveness and safety.

PURPOSE: To assess the efficacy and safety of multiple subpial transection (MST), a new technique in epilepsy surgery, alone and in combination with resection. METHODS: MST was performed in 22 patients with intractable epilepsy, 10 of whom were treated with a combination of a resection and MST in functionally important cortex, 6 of whom were treated with a combination of a resection and MST performed outside functionally important cortex, and 6 of whom were treated with MST alone. RESULTS: Of the 6 patients who received MST alone, none became seizure free and 4 showed > 50% reduction of all seizure types. In 2 patients, including 1 with Rasmussen's encephalitis, no change in seizure frequency or intensity occurred. Of the 16 patients in whom MST was combined with a resection, 9 (56%) became seizure free. Six of the remaining 7 patients showed > 95% reduction of all seizure types. Disappearance of epileptiform potentials in the postoperative EEG correlated significantly with complete relief from seizures. Subtle, permanent neurological deficits remained in 5 of 14 patients who received MST in functionally important brain areas. CONCLUSIONS: Reduction of the seizure frequency was substantial in 4 of 6 patients who received MST alone, but complete seizure control was not observed. MST surrounding a lesionectomy may be a new surgical approach which would minimize the excised volume and improve seizure control.

Adolescent↗
PubMed1997

Safety of intrahippocampal depth electrodes for presurgical evaluation of patients with intractable epilepsy.

PURPOSE: Intracerebral depth electrodes are used in preoperative evaluation of selected patients with intractable epilepsies. In spite of their usefulness, safety of depth electrodes is disputed, and the number of insertions is decreasing. This study examined retrospectively possible deleterious effects such as perioperative complications, induction of epileptogenesis, and neuropsychologic deficits. METHODS: Clinical course and neuroradiologic findings of 115 patients with bilaterally inserted longitudinal intrahippocampal depth electrodes (IDEs) were analyzed. Hippocampal resection specimens were examined histopathologically. To detect newly developed epileptogenic areas, EEG recordings, seizure control, and semiology after standardized resection procedures were compared between patients who received IDEs and those who did not. To demonstrate functional deficits caused by IDE insertion into an unaffected hippocampus of the speech-dominant hemisphere, changes of verbal learning and memory performances before and after right amygdalohippocampectomy were compared between patients evaluated with and without IDEs. RESULTS: Five significant complications without any permanent neurologic deficit were noted, and only one was specifically linked to IDE insertion. The tissue damage associated with the insertion was minimal and sharply circumscribed. No differences of seizure outcome after standardized resections were identified between patients with and without IDEs. In postoperative EEG recordings, there was no evidence of new epileptogenic areas. No verbal memory deficit caused by IDE implantation into the hippocampus of the speech-dominant hemisphere was detectable. CONCLUSIONS: Results indicate that it is safe to implant these IDEs in selected patients.

Adult↗
PubMed1997

Petroclival meningiomas: is radical resection always the best option?

BACKGROUND: The surgical management of petroclival meningiomas is, despite the invaluable technical achievements in the past decade, still burdened by a high operative morbidity. It seems doubtful whether radical surgical removal should always be the primary goal in those lesions as advocated until very recently. METHODS: A series was critically analysed and the literature discussed to elucidate criteria for a different attitude. Between 1990 and 1995 a total of 19 patients harbouring petroclival meningiomas were operated on. The following approaches were used: petrosal (n = 13), retrosigmoidal (n = 5), and subtemporal (n = 1). Thirteen lesions were removed completely and six incompletely as assessed by postoperative MRI. RESULTS: No recurrence or regrowth could be detected on MRI after a mean follow up of 18 months. Surgical mortality occurred in one patient (5%) and there was early postoperative dysfunction in 56%. At the time of follow up major permanent operative morbidity was present in two patients (11%). CONCLUSIONS: In accord with recent literature subtotal resection of petroclival meningiomas should be contemplated in a subset of patients (with invasion of brain stem or cavernous sinus) to reduce the incidence of disabling deficits. Surgery should not be delayed in younger patients because surgical morbidity relates positively with tumour size.

Adult↗
PubMed1997

Efficacy of conservative treatment of lumbar disc herniation.

MATERIALS AND METHODS: This study comprises a total of 322 patients who were seen in our neurosurgical department as inpatients (N = 241) or outpatients (N = 81) for lumbar disk herniation. Patients presenting with major neurological deficits and/or symptoms reflecting lumbar stenosis were excluded. All patients were scheduled for conservative treatment which was based on bedrest for a minimum of two weeks. Thereafter, patients were assigned for further nonoperative or operative treatment. RESULTS: According to our results only 49% of conservatively treated patients had to be operated on. At long-term follow-up with a mean observation time of 2 years as available in 125 patients, 93% of patients who did not undergo surgery were improved with respect to pain. Motor function had recovered in 60%, and sensory deficits in 58% of these cases. CONCLUSIONS: In conclusion, conservative treatment is effective and in our opinion mandatory in the setting of sciatica caused by lumbar disc herniation except for patients presenting with severe, or progressive neurological deficits.

Adult↗
PubMed1996

Presynaptic 5-HT auto- and heteroreceptors in the human central and peripheral nervous system.

In view of the potential pathophysiological and therapeutic implications, presynaptic 5-HT auto- and heteroreceptors have been identified and characterized in isolated human tissues and their functional role has been determined. Such investigations have been carried out in different laboratories including that of the authors. Basic evidence for the involvement of inhibitory 5-HT receptors in modulation of 5-HT release in the cerebral cortex was obtained in slices: exogenous 5-HT inhibited 5-HT release in a manner susceptible to blockade by methiothepin, which given alone facilitated 5-HT release, probably by preventing endogenous 5-HT from activating the inhibitory receptors. The latter receptors are located on the 5-HT nerve terminals themselves, since 5-HT (and sumatriptan) also inhibited 5-HT release from cortical synaptosomes. Their pharmacological properties conform to those of the 5-HT1D class. Subclassification (5-HT1D alpha or 5-HT1D beta) has been tried with ketanserin which has an at least 60 times higher affinity for 5-HT1D alpha (pki = 7.1) than 5-HT1D beta receptors. Since ketanserin (0.32 microM) did not affect the concentration-response curve for 5-carboxamidotryptamine (5-CT), the presynaptic 5-HT autoreceptor may belong to the 5-HT1D beta rather than the 5-HT1D alpha subtype. The sympathetic nerve terminals of the human saphenous vein are endowed with inhibitory 5-HT1D beta heteroreceptors, as indicated by the potency ratio of several 5-HT receptor agonists in inhibiting noradrenaline release in strips of this blood vessels and by the ability of methiothepin, but not of ketanserin 0.3 microM, to act as an antagonist. Noradrenergic nerves in the dura mater, which probably innervate its microvasculature, may also be endowed with inhibitory 5-HT receptors, since 5-HT inhibited noradrenaline release from this tissue. In strips of atrial appendages, 5-HT receptor agonists (e.g. 5-HT, 5-CT and sumatriptan) inhibited noradrenaline release at potencies which are correlated with their ki values at 5-HT1D alpha and 5-HT1D beta receptors. Since this inhibitory effect was antagonized by ketanserin (0.3 but not 0.03 microM) and methiothepin, the presynaptic 5-HT receptor in this tissue may belong to the 5-HT1D alpha subtype. However, this conclusion needs further confirmation by experiments with more potent and subtype-selective antagonists of 5-HT1D alpha and 5-HT1D beta receptors.

Central Nervous System↗