PubMed Health⌕ Search

Biomedical subjects

E W Lang

Publications and source records attributed to E W Lang.

At least 19 recordsLinked to original sources
PubMed2000

Giant cystic craniopharyngiomas with extension into the posterior fossa.

Between 1991 and 1998, 24 patients underwent surgery for a craniopharyngioma in our department. This group included two patients who had tumors with extensive growth along the midline, and along the posterior fossa in particular. In both cases suprasellar calcifications were typical features on magnetic resonance imaging (MRI) and computed tomography (CT). A 7-year-old boy presented with a 6-month history of headache, nausea, and progressive unilateral hearing loss. With a suboccipital approach it was possible to remove the main part of the tumor. In a 13-year-old boy headache and visual deterioration led to the diagnosis of a craniopharyngioma, which was removed with a pterional approach. For the neuroimaging work-up in such cases of atypically growing craniopharyngiomas MRI is the method of choice. Additional CT scanning is recommended, which provides valuable information about bony changes at the skull base due to space-occupying growth. CT substantiates the differential diagnosis if typical calcifications are seen.

Adolescent↗
PubMed1999

A massive intrathecal cefazoline overdose.

This case report describes the clinical course of a patient who inadvertently received a massive intrathecal cefazoline overdose through a lumbar drain, which had been placed after trans-sphenoidal surgery for a pituitary adenoma. She received high-dose barbiturate therapy and was monitored with electroencephalography (EEG), somatosensory evoked potentials (SSEP), brainstem auditory evoked potentials (BAEP) and transcranial Doppler ultrasound (TCD). No cerebrospinal fluid (CSF) exchange was performed, but CSF was drained continuously with daily CSF-cefazoline level monitoring. Despite the extremely toxic dose, the patient soon recovered completely.

Adenoma↗
PubMed1999

Spontaneous oscillations of arterial blood pressure, cerebral and peripheral blood flow in healthy and comatose subjects.

Slow and rhythmic spontaneous oscillations of cerebral and peripheral blood flow occur within frequencies of 0.5-3 min-1 (0.008-0.05 Hz, B-waves) and 3-9 min-1 (0.05-0.15 Hz, M-waves). The generators and pathways of such oscillations are not fully understood. We compared the coefficient of variance (CoV), which serves as an indicator for the amplitude of oscillations and is calculated as the percent standard deviation of oscillations within a particular frequency band from the mean, to study the impairment of generators or pathways of such oscillations in normal subjects and comatose patients in a controlled fashion. With local ethic committee approval, data were collected from 19 healthy volunteers and nine comatose patients suffering from severe traumatic brain injury (n = 3), severe subarachnoid hemorrhage (n = 3), and intracerebral hemorrhage (n = 3). Cerebral blood flow velocities were measured by transcranial Doppler ultrasound (TCD), peripheral vasomotion by finger tip laser Doppler flowmetry (LDF), and ABP by either non-invasive continuous blood pressure recordings (Finapres method) in control subjects, or by direct radial artery recordings in comatose patients. Each recording session lasted approximately 20-30 min. Data were stored in the TCD device for offline analysis of CoV. For CoV in the cerebral B-wave frequency range there was no difference between coma patients and controls, however there was a highly significant reduction in the amplitude of peripheral B-wave LDF and ABP vasomotion (3.8 +/- 2.1 vs. 28.2 +/- 16.1 for LDF, p < 0.001; and 1.2 +/- 0.7 vs. 4.6 +/- 2.8 for ABP, p < 0.001). This observation was confirmed for spontaneous cerebral and peripheral oscillations in the M-wave frequency range. The CoV reduction in peripheral LDF and ABP oscillations suggest a severe impairment of the proposed sympathetic pathway in comatose patients. The preservation of central TCD oscillations argues in favor of different pathways and/or generators of cerebral and peripheral B- and M-waves.

Adult↗
PubMed1998

Unspecific long-term potentiation can evoke functional segregation in a model of area 17.

It has been shown recently in rat hippocampus that the synapse specificity of Hebbian long-term potentiation breaks down at short distances (< 100 microm). Using a neural network model we show that this unspecific component of long-term potentiation can be responsible for the robust formation and maintainance of cortical organization during activity-driven development. When the model is applied to the formation of orientation and ocular dominance in visual cortex, addition of an unspecific component to standard Hebbian learning, in combination with a tendency of left-eye and right-eye driven synapses to initially group together on the postsynaptic neuron, induces the simultaneous emergence and stabilization of ocular dominance and of segregated, oriented ON/OFF subfields. Since standard Hebbian learning cannot account for the simultaneous stabilization of both structures, unspecific LTP thus induces a qualitatively new behaviour. Since unspecific LTP only acts between synapses which are locally clustered in space, our results imply that details of the local grouping of synapses on the dendritic arbors of postsynaptic cells can considerably influence the formation of the cortical functional organization at the systems level.

Algorithms↗
PubMed1998

[Interhemispheric subdural hematoma].

The interhemispheric subdural hematoma (ISH) is a special subdural hematoma with regard to both location and symptomatology. The most widely described clinical signs and symptoms associated with an ISH are a lucid interval and the falx syndrome. The latter is featured by a contralateral hemiparesis that is accentuated in the lower extremity but spares the face. Minor head trauma or a preexisting coagulation disorder are also often found. Nonsurgical treatment should be chosen in patients with little neurologic dysfunction and a stable clinical course. Patients with progressive neurologic deterioration and focal neurologic deficits should be operated on without delay. This article provides a review of 99 published cases of ISH and adds 3 cases to the existing literature.

Cerebral Cortex↗
PubMed1998

A neural network model for the emergence of grating cells.

A correlation-based learning (CBL) neural network model is proposed, which simulates the emergence of grating cells as well as some of their response characteristics to periodic pattern stimuli. These cells, found in areas V1 and V2 of the visual cortex of monkeys, respond vigorously and exclusively to bar gratings of a preferred orientation and periodicity. Their non-linear behaviour differentiates grating cells from other orientation-selective cells, which show linear spatial frequency filtering.

Animals↗
PubMed1998

Simulations on the selectivity of 5-aminolaevulinic acid-induced fluorescence in vivo.

The knowledge of the exact time course of a photosensitizer in tumour and surrounding host tissue is fundamental for effective photodynamic therapy (PDT) and fluorescence-based diagnosis. In this study the time course of porphyrin fluorescence following topical application of 5-aminolaevulinic acid (ALA) using different formulations, concentrations and incubation times has been measured in amelanotic melanomas (A-Mel-3) (n = 54) grown in transparent dorsal skinfold chambers of Syrian golden hamsters and in human basal cell carcinomas (BCCs) (n = 40) in vivo. To simulate the accumulation of ALA-induced protoporphyrin IX (Pp IX), a three-compartment model has been developed and rate constants have been determined. The kinetics of both the A-Mel-3 tumours and the BCCs show a significantly higher fluorescence intensity in tumour as compared to normal surrounding host tissue. Maximal fluorescence intensity in A-Mel-3 tumours as a percentage of the reference standard used occurs 150 min post incubation (p.i.) using a 1, 3 or 10% (vol.) ALA solution buffered to pH 7.4 and 1 h incubation time. After a 4 h incubation time maximal fluorescence intensity in tumour is measured shortly p.i. A concentration of 10% ALA does not increase the fluorescence intensity as compared to 3% ALA following 4 h incubation, but either 3 or 10% ALA yields a significantly higher fluorescence after 4 h incubation time as compared to 1 h. The fluorescence intensity following an 8 h incubation reaches its maximum directly p.i. for all concentrations and then decreases exponentially. The fluorescence intensity in the surrounding host tissue shows no statistically significant difference regarding concentration or incubation time. At least during the first hour p.i., the fluorescence intensity measured in the surrounding tissue is lower as compared to that in the tumour in all groups. 24 h after topical application hardly any fluorescence is detectable in tumour or surrounding host tissue in all experimental groups. Incubating human BCCs with a 20% ALA cream (water-in-oil emulsion) or a 20% ALA gel (containing 40% dimethyl sulfoxide) for approximately 2 h yields a similar fluorescence intensity directly after incubation for either cream or gel. However, while yielding a maximum 120 min p.i. with cream, the fluorescence intensity increases for a longer time (about 2-3 h p.i.) and up to higher values using the gel formulation. In surrounding normal skin, cream as well as gel formulation yields a similar fluorescence intensity directly after incubation. Afterwards the fluorescence intensity decreases slowly using the cream whereas a further increase of the fluorescence intensity is measured in the normal skin with a maximum 240 min p.i. using the gel formulation. The results of the proposed three-compartment model indicate that the observed selectivity of accumulated porphyrins following topical application of ALA is mainly governed by an increased ALA penetration of the stratum corneum of the skin, an accelerated ALA uptake into the cell and a higher porphyrin formation in tumour as compared to normal skin tissue, but not by a reduced ferrocheletase activity.

Aminolevulinic Acid↗
PubMed1998

The utility of contrast-enhanced MR-angiography for posterior fossa giant cerebral aneurysm management.

The utility of magnetic resonance angiography is sometimes limited in the diagnostic workup of cerebral aneurysms with low flow and/or partial thrombosis when weighed against digital subtraction angiography. We present the case of a rare superior cerebellar artery giant, partially thrombosed aneurysm in which additional i.v. contrast-enhanced MRA sequences were comparable to digital subtraction angiography. It demonstrated not only the exact spatial resolution and correct anatomical relation but also the hemodynamics which were confirmed by intraoperative Doppler ultrasound. This report supports the feasibility and utility of i.v. contrast-enhanced MRA for posterior fossa giant cerebral aneurysm management.

Cerebellum↗
PubMed1997

Outcome after severe head injury: an analysis of prediction based upon comparison of neural network versus logistic regression analysis.

More reliable prediction of outcome would be helpful for clinicians who treat severely head-injured patients. To determine if neural network modeling would improve outcome prediction compared with standard logistic regression analysis and to determine if data available 24 h after severe head injury allows better prediction than data obtained within 6 h, we tested the ability of both techniques at these two times to predict outcome (dead versus alive) at 6 months. One thousand sixty-six consecutive patients with Glasgow Coma Scale scores of 8 or less during the first 24 h after injury were randomly divided into two groups. Data from the first group (n = 799) were used to develop the models; data from the second group (n = 267) were used to test the accuracy, sensitivity, and specificity of the models by comparing predicted and actual outcomes. The 6-month mortality rate was 63.5%. Our findings confirm the importance of age, Glasgow Coma Scale scores, and hypotension in predicting outcome. Using data available at 24 h improved the predictive power of both models compared with admission data; at both time points, however, the differences in the results obtained with the two models were negligible. We conclude that outcome (dead versus alive) at 6 months after severe head injury can be predicted with logistic regression or neural network models based on data available at 24 h. Critical therapeutic decisions, such as cessation of therapy, should be based on the patient's status 1 day after injury and only rarely on admission status alone.

Adolescent↗
PubMed1996

Myogenic motor-evoked potential monitoring using partial neuromuscular blockade in surgery of the spine.

STUDY DESIGN: The authors analyzed motor-evoked potentials using transcranial electrical cortical stimulation during spinal surgery in 40 patients under conditions of partial neuromuscular blockade. OBJECTIVES: The results were used to investigate the utility of motor-evoked potential monitoring to prevent neurologic injury in spinal surgery. SUMMARY OF BACKGROUND DATA: Noninvasive transcranial electrical motor-evoked potentials are reportedly effective in predicting postoperative spinal cord deficits caused by intraoperative occurrences. However, the sensitivity and specificity of these predictions have not been assessed under conditions of partial neuromuscular blockade during a wide variety of surgical procedures. METHODS: Compound muscle action potentials were recorded at the tibialis anterior muscle while general anesthesia was maintained with nitrous oxide, etomidate, and sufentanil. Surgery was performed at all spinal levels for a variety of diagnoses. RESULTS: Reference motor-evoked potential amplitudes, measured after induction of partial neuromuscular blockade, ranged from 25 to 7562 microV (median, 600 microV). Variation in intraoperative motor-evoked potential amplitude ranged from signal loss to a 3440% increase. A decrease to less than 20% of the individual reference value for motor-evoked potential amplitude occurred at least once in nine patients (22.5%) but as not associated with postoperative motor deficits. Two patients who had loss of motor-evoked potential signal without recovery did have postoperative motor deficits. Motor-evoked potentials predicted postoperative motor improvement in six patients. An improvement threshold of 160% of the reference amplitude predicted postoperative motor improvement with 100% sensitivity and 81% specificity. CONCLUSIONS: The authors support the utility of recording transcranial electrical motor-evoked potentials in spinal surgery under partial neuromuscular blockade. Recovery of lost motor-evoked potentials was not associated with postoperative motor deficits, whereas non-recovery of lost motor-evoked potentials was.

Adolescent↗
PubMed1996

Intervertebral disc space infection caused by Aspergillus fumigatus.

The authors describe the case of a 53-year-old woman who suffered from an Aspergillus fumigatus infection of the L2/3 intervertebral disc space unrelated to previous operations on her lumbar spine. After surgical debridement combined with amphotericin therapy she died on the 23rd postoperative day from a fulminant bacterial sepsis of pulmonary origin. Although she had intermittently used steroids for bronchial asthma, this is an unusual case of fungal infection of the lumbar spine in an apparently immunocompetent patient.

Amphotericin B↗
PubMed1996

Urinary retention and space-occupying lesions of the frontal cortex.

The authors present 2 cases in which urinary retention was related to supratentorial cortical lesions. These cases support the presence and function of a supratentorial center involved in control of the voiding reflex loop and indicate that lesions affecting this center can result in urinary retention rather than the syndrome of incontinence, urgency, and increased urinary frequency that is generally attributed to dysfunction of this system. In such cases, a clinical presentation of urinary retention in the absence of associated remarkable neurological deficits renders clinical evidence as a localizing sign.

Aged↗
PubMed1995

Variability of vascular territory in stroke. Pitfalls and failure of stroke pattern interpretation.

BACKGROUND AND PURPOSE: We investigated the efficacy and feasibility of determining infarction mechanisms and underlying embolic or hemodynamic pathologies from topographical patterns of ischemic damage seen on computed tomography or magnetic resonance imaging. METHODS: Infarction patterns from 22 patients with ipsilateral severe, hemodynamically relevant carotid stenosis (n = 6) or occlusions (n = 16) were superimposed, using two matching algorithms, onto maps showing the variability of the cerebral vascular territories as determined from recent cadaver studies. These images were used to classify the infarctions as border-zone or territorial for the two conditions of minimal and maximal middle cerebral artery distribution. RESULTS: Classification of infarction patterns resulting from carotid stenosis was independent of the territorial extension map chosen: 83% were classified as territorial. Classification of patterns due to carotid occlusion, however, varied highly; 81% of infarctions were considered territorial when the maximal middle cerebral artery distribution map was used, whereas only 19% were when the minimal territorial extension map was used. CONCLUSIONS: The current concept that stroke mechanisms can be inferred from the interpretation of stroke patterns seen on computed tomography scans or magnetic resonance imaging is significantly confounded by the demonstrated variability in intracranial vascular distributions. Stroke pattern interpretation appears to be highly dependent on the in vivo vascular tree of the individual, which is unknown to the examiner. This calls into question the reliability of classifying infarction patterns as border-zone or territorial. Determination of true underlying stroke mechanisms requires a comprehensive approach and cannot be based solely on stroke pattern interpretation.

Brain↗
PubMed1995

Intracranial pressure and cerebral perfusion pressure in severe head injury.

Monitoring and management of intracranial pressure (ICP) are fundamental to modern neurotraumatology. Although never formally proven to independently improve outcome in prospective, randomized, placebo-controlled trials, there is such a predominance of indirect support for this modality that most neurotrauma protocols are impossible with-out its inclusion and ethical considerations virtually preclude placebo-controlled trials of its efficacy. In addition to the question of improving outcome, ICP monitoring is also useful in guiding the use of potentially harmful treatment modalities such as hyperventilation, mannitol, and barbiturates, and also provides important prognostic data. ICP monitoring provides information on the likelihood of cerebral herniation and allows calculation of the cerebral perfusion pressure (CPP). Although there is no constant threshold for herniation, the most commonly used treatment threshold is 20 to 25 mm Hg. In addition, ICP trends are indispensable in providing the earliest possible indication of critical intracranial mass effects when combined with other clinical indicators. CPP is the difference between mean arterial pressure and ICP. CPP is an important clinical indicator of cerebral blood flow (CBF). Cerebral autoregulation generally remains at least partially preserved after severe head injury, although the CPP value at which it is activated appears to be shifted upward. Therefore, maintaining adequate CBF appears to require using an elevated minimal CPP threshold when treating the injured brain. A generally accepted value of 70 mm Hg is suggested.

Brain Ischemia↗
PubMed1994

Intracranial pressure. Monitoring and management.

Monitoring of ICP from the subarachnoid, intraparenchymal, or ventricular spaces can be accomplished easily and reliably. The risks and benefits of each approach should be considered when choosing the monitoring technique. The goal of ICP management is to prevent herniation and to optimize cerebral perfusion. Even transient episodes of post-traumatic cerebral ischemia due to inadequate CPP can quickly nullify all resuscitative efforts. The provision of sufficient CBF is complicated by the varying degree of disruption of pressure autoregulation commonly resulting from head trauma. Post-injury, there is a need to provide a CPP which is elevated to some extent with respect to that sufficient in uninjured brains. This generally requires a CPP of at least 70 mm Hg, which must be accomplished by maintaining an adequate MAP while controlling ICH. Although ICH can generally be controlled using methods commonly employed, the majority of these techniques have potential complications. Additionally, there is increasing evidence that significant variation exists in the pathologic processes driving ICH in individual patients. Therefore, goals such as the desired CPP and conditions such as the relative contribution of edema, cerebral hypervolemia, and ischemia to ICH should optimally be considered in a patient-specific fashion and allow a targeted approach to therapy.

Barbiturates↗
PubMed1993

Emergence of orientation selective simple cells simulated in deterministic and stochastic neural networks.

The processing of visual data in area 17 of the mammalian cortex is mainly performed by cells with receptive fields which are tuned to different orientations of input stimuli. The mechanisms underlying the emergence of receptive field properties of orientation selective cells are not well understood up to now. Recently, some models for the prenatal development of the receptive fields of orientation selective simple cells have been proposed, which emerge in neural networks trained by Hebb type unsupervised learning rules. These models, however, use different network architectures and are restricted to the case of identical input neurons. In this work, a biologically motivated neural network model with a general architecture is presented. It is trained with a Hebb type updating rule and with uncorrelated input. The input neurons are identified with retinal ganglion cells and exhibit mature Mexican hat type receptive fields. If the receptive fields of the input neurons have identical properties (deterministic model), a set of parameter domains is found, which characterize different kinds of receptive field maturation behaviour of the network. Results obtained by other authors with similar models are contained in this description as special cases. In addition, the more general and rarely investigated stochastic model, where random variations of the parameters describing the receptive fields of the input neurons occur, is investigated. A high sensitivity of the network against these random variations is obtained. In case of large variations of receptive field parameters of the ganglion cells, a qualitatively new kind of maturation behaviour appears. A significant part of the synaptic connections from ganglion cells to the cortical cell is removed and small simple cell receptive fields with only few lobes emerge. The stochastic model is found to provide a better description of the size, scatter and structure of receptive fields present in biological systems, than the deterministic model.

Animals↗