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Biomedical subjects

M Knauth

Publications and source records attributed to M Knauth.

At least 19 recordsLinked to original sources
PubMed2003

Pronounced arterial collateralization was induced after permanent rat cerebral four-vessel occlusion. Relation to neuropathology and capillary ultrastructure.

The present study investigates chronic changes in cerebral arterial vessel system, microvasculature, and brain histopathology using an adult rat model based on permanent and stepwise occlusion of four cerebral vessels. Digital subtraction angiography (DSA) was performed to study chronic changes in arterial cerebral vessel system after permanent vessel occlusion. Long-lasting functional changes such as NMDA-, AMPA- and GABA(A)-receptor binding were detected in hippocampus and dentate gyrus using autoradiography. Structural changes in cerebral capillaries were investigated using light- and electron microscopy. Chronic cerebral oligemia did not cause any significant changes in the densities of excitatory glutamate and inhibitory GABA(A) receptors. By electron microscopy we could document, however, that most capillaries in vessel-occluded animals shrank, the endothelial cells were prominent with enlarged nuclei and increased cytoplasm, and the basal membrane was thickened. In contrast to the degenerative changes in brain capillaries, pronounced arterial collateralization was disclosed by DSA after chronic brain vessel occlusion. The model of chronic occlusion of four cerebral vessels is characterized by capillary degeneration and arterial collateralization proceeding in parallel. Thus, this rat model may be useful in investigations of long-lasting compensatory mechanisms contributing to cerebrovascular or neurodegenerative disorders.

Angiography, Digital Subtraction↗
PubMed2002

Precocial diving and patent foramen ovale in bearded seal (Erignathus barbatus) pups.

In this study we used a Doppler ultrasonic device, in combination with a sonographic contrast medium, to test whether free-living bearded seal (Erignathus barbatus) pups have a closed (anatomically or functionally) foramen ovale. A total of 17 examinations were performed on 12 individual pups with a body mass range of 29-103 kg (0-21 days old). These examinations showed that young bearded seal pups dive with a patent foramen ovale (PFO), and that this structure starts to close, at least functionally, during the 2nd week of life. The wide range in the timing of closure (one animal 21 days old still had a PFO) indicates that a closed foramen ovale is not crucial for the diving that these seals perform at this age. The primary function of diving during the 1st week of life is to avoid surface predation and only moderate diving ability is sufficient to achieve this goal. However, some of the diving performed by bearded seal pups with a PFO would likely be sufficient to create intravenous bubble formation during breath-hold diving in humans. Special adaptations in the seals, such as collapsible lungs and diving with minimal lung air volume, probably prevent this from happening.

Animals↗
PubMed2002

CT and diffusion-weighted MR imaging in randomized order: diffusion-weighted imaging results in higher accuracy and lower interrater variability in the diagnosis of hyperacute ischemic stroke.

BACKGROUND AND PURPOSE: Diffusion-weighted MRI (DWI) has become a commonly used imaging modality in stroke centers. The value of this method as a routine procedure is still being discussed. In previous studies, CT was always performed before DWI. Therefore, infarct progression could be a reason for the better result in DWI. METHODS: All hyperacute (<6 hours) stroke patients admitted to our emergency department with a National Institutes of Health Stroke Scale (NIHSS) score >3 were prospectively randomized for the order in which CT and MRI were performed. Five stroke experts and 4 residents blinded to clinical data judged stroke signs and lesion size on the images. To determine the interrater variability, we calculated kappa values for both rating groups. RESULTS: A total of 50 patients with ischemic stroke and 4 patients with transient symptoms of acute stroke (median NIHSS score, 11; range, 3 to 27) were analyzed. Of the 50 patients, 55% were examined with DWI first. The mean delay from symptom onset until CT was 180 minutes; that from symptom onset until DWI was 189 minutes. The mean delay between DWI and CT was 30 minutes. The sensitivity of infarct detection by the experts was significantly better when based on DWI (CT/DWI, 61/91%). Accuracy was 91% when based on DWI (CT, 61%). Interrater variability of lesion detection was also significantly better for DWI (CT/DWI, kappa=0.51/0.84). The assessment of lesion extent was less homogeneous on CT (CT/DWI, kappa=0.38/0.62). The differences between the 2 modalities were stronger in the residents' ratings (CT/DWI: sensitivity, 46/81%; kappa=0.38/0.76). CONCLUSIONS: CT and DWI performed with the same delay after onset of ischemic stroke resulted in significant differences in diagnostic accuracy. DWI gives good interrater homogeneity and has a substantially better sensitivity and accuracy than CT even if the raters have limited experience.

Acute Disease↗
PubMed2001

Acute disseminated encephalomyelitis: a follow-up study of 40 adult patients.

OBJECTIVES: To describe the clinical, CSF, and radiologic findings and long-term follow-up in a cohort of patients with acute disseminated encephalomyelitis (ADEM), and to determine possible prognostic factors for progression to MS. METHODS: Forty adults (28 women, mean age 33.5 years) diagnosed with ADEM were analyzed. Clinical symptoms, cranial MRI and CSF findings, and the response to a standardized treatment during the acute phase of the disease were analyzed by chart review. The final diagnosis of ADEM or clinically definite MS was established upon follow-up examination after 8 to 137 months. The patients with ADEM and MS were compared to detect differences between the two groups. RESULTS: Fifteen patients had a preceding infection (n = 14) or immunization (n = 1). The most frequent clinical signs were motor deficit (80%), followed by sensory deficits, brainstem signs, and ataxia. CSF findings were highly variable; normal results were present in 20% of patients. Oligoclonal bands were positive in 65% of patients. Ninety-five percent of all patients improved during the acute phase of the disease. Upon follow-up, 14 patients had developed clinically definite MS. Of the 26 patients with the final diagnosis of ADEM, two patients had died, nine had minor deficits, three had moderate deficits, and 12 patients had no remaining symptoms. Patients with the final diagnosis of ADEM were older, and more often had a preceding infection, clinical signs of brainstem involvement, a higher CSF albumin fraction, and infratentorial lesions. CONCLUSIONS: Many patients initially diagnosed with ADEM develop clinically definite MS upon long-term follow-up. The authors found no useful diagnostic criteria for the differentiation of a first episode of MS from monophasic ADEM. The term ADEM may still be employed as a description of a clinical syndrome, but should not be used as a distinct entity until reliable diagnostic criteria have been developed.

Adult↗
PubMed2001

Low-field interventional MRI in neurosurgery: finding the right dose of contrast medium.

MRI is increasingly being used as an interventional tool in neurosurgery. The field strength of "intraoperative" MR systems is usually lower than that of imagers commonly used for diagnostic purposes. However, lesion enhancement and apparent lesion extent depend on field strength. The aim of this study was to compare the contrast between intracranial, contrast-enhancing space-occupying lesions and the surrounding white matter obtained with low-field (0.2 T) and high-field (1.5 T) MR imaging and to find the contrast medium dosage for low-field MRI that produces the same lesion-to-white-matter contrast as the one obtained with high-field MRI after the administration of a standard dose of the contrast medium. A total of 38 patients with intracranial metastases or high-grade glioma were enrolled in this study. T1-weighted spin-echo sequences were acquired. High-field (1.5 T) studies were performed after the i.v. administration of 0.1 mmol gadolinium-DTPA/kg body weight. For low-field MRI (0.2 T) a dose escalation technique was used. T1-weighted sequences were repeated after each of three i. v. injections of 0.1 mmol gadolinium-DTPA/kg body weight. Thus, at the low-field examinations three T1-weighted sequences with a contrast medium dosage of 0.1, 0.2 and 0.3 mmol gadolinium-DTPA/kg body weight were obtained. Lesion-to-white-matter contrasts were calculated and compared. The average lesion-to-white-matter contrast obtained with high-field MR examinations was 1.63 (standard deviation 0.32). In the low-field MR examinations the average lesion-to-white-matter contrast was 1.34 (0.2) after a single dose, 1.57 (0.2) after a double dose, and 1.71 (.19) after a triple dose of contrast medium. The lesion-to-white-matter contrast of the high-field MR examination after a single dose of contrast medium was significantly higher than that of the low-field study after a single dose (P < 0.0001), but did not differ significantly from the low-field studies after a double (P = 0.28) or a triple dose (P = 0.17) of contrast medium. In a series of patients with contrast-enhancing space occupying brain lesions low-field MRI (0.2 T) after a double dose of contrast medium yielded the same lesion-to-white-matter contrasts as high-field MRI (1.5 T) after a standard dose. This is an important finding to avoid errors in intraoperative MRI due to the immanently lower degree of lesion enhancement in low-field MR imaging.

Adult↗
PubMed2001

[Acute disseminated encephalomyelitis (ADEM)].

Acute disseminated encephalomyelitis (ADEM) is an unusual demyelinating disease of the CNS. We review clinical symptoms, findings from radiological and CSF examinations, and current treatment strategies for ADEM. This disorder is often associated with a precedent infection or vaccination but may also occur spontaneously. The clinical symptoms are highly variable. Analysis of CSF usually reveals lymphocytic pleocytosis and an elevated protein content but may also yield normal results. Magnetic resonance imaging shows solitary or multiple lesions within the CNS. Most patients improve quickly with methylprednisolone. If that fails, immunoglobulin, plasmapheresis, or cytostatic drugs can be employed. Unlike MS, ADEM has a monophasic course and favourable long-term prognosis. Multiphasic courses are very rare. There are no diagnostic criteria to distinguish ADEM reliably from MS during the acute phase. We presume that ADEM is a variant of MS and not an independent disease entity.

Adult↗
PubMed2001

Comparison of CT with diffusion-weighted MRI in patients with hyperacute stroke.

Tissue changes in ischaemic stroke are detectable by diffusion-weighted MRI (DWI) within minutes of the onset of symptoms. However, in daily routine CT is still the preferred imaging modality for patients with acute stroke. Our purpose of this study was to determine how early and reliably ischaemic brain infarcts can be identified by CT and DWI. Three neuroradiologists, blinded to clinical signs but aware that they were dealing with stroke, analysed the CT and DWI of 31 patients with an acute ischaemic stroke. We calculated kappa-values to analyse inter-rater variability. The ratings were compared with follow-up studies showing the extent of the infarct. The combined assessment of all observers gave positive findings in 77.4% of all CT examinations, with kappa = 0.58. Areas of high signal were seen on all DWI studies by all observers (kappa = 1). Estimation of the extent of the infarct based on DWI yeilded kappa = 0.70 and that based on CT kappa = 0.39. DWI was much more reliable than CT in the detection of early ischaemic lesions and we believe that it should be used in acute ischaemic stroke before aggressive therapeutic intervention.

Aged↗
PubMed2001

Hypoxic brain damage after intramuscular self-injection of diclofenac for acute back pain.

We present a case of hypoxic brain damage that occurred after intramuscular injection of diclofenac due to a severe anaphylactic reaction. A 38-year-old nurse treated herself for acute lower back pain with 100 mg diclofenac intramuscularly. Five minutes later, she collapsed and developed coma and respiratory arrest. After cardiopulmonary resuscitation she was transferred to hospital. On admission she was comatose and received controlled ventilation of the lungs. Magnetic resonance imaging and computerized tomography showed signs of hypoxic brain injury and the patient died from central cardiopulmonary failure 7 days later. Intramuscular treatment with non-steroidal anti-inflammatory drugs such as diclofenac has rare but potentially severe side-effects. Therefore, intramuscular injections are inappropriate and should be replaced with oral or rectal treatment, which has similar absorption profiles.

Acute Disease↗
PubMed2001

[Clinically silent cerebral embolisms after cerebral catheter angiography].

PURPOSE: To assess for the incidence of clinically silent cerebral lesions after cerebral catheter angiography. METHODS: MRI including PD-, T2-, and diffusion-weighted images was performed shortly before and after 27 cerebral catheter angiographies. RESULTS: After 5/27 angiographies (18.5%) we found 6 new, presumably embolic cerebral lesions with a typical diameter of 2-3 mm on diffusion-weighted images. No correlation was found between the occurrence of these lesions and a preexisting arteriosclerotic cerebrovascular disease, fluoroscopy time, or number of angiographic series. CONCLUSION: Cerebral angiography appears to be associated with a relatively high risk (about 20%) of clinically silent cerebral embolism. This risk is higher than has been estimated based on the incidence of neurological deficits (0.1-0.3%) after cerebral angiography. The safety of cerebral angiography needs to be improved. Diffusion-weighted MR imaging is suitable to monitor the safety of angiographic procedures and material.

Adolescent↗
PubMed2001

[Similarity of the brains of twins].

PURPOSE: To test the assumption underlying every morphometric twin study that the brains of monozygotic twins are almost identical. METHODS: High resolution MRI of the neurocranium of 26 monozygotic twin pairs were acquired and the volumes of 36 cerebral structures were measured. The same twins served as control group after rear-ranging them into non-related pairs of same sex and matching them for age, body height and body weight. RESULTS: For most of the examined structures the correlations within the twins were significant (R = 0.97-0.59). Except for total forebrain volume the controls showed no significant similarity. CONCLUSIONS: For almost every measured cerebral structure the assumption, that significant similarities exist between healthy monozygotic twins is correct. Therefore discordant monozygotic twins represent an excellent sample when investigating cerebral correlates of neurologic and psychiatric disorders.

Adult↗
PubMed2001

Monocrystalline iron oxide nanoparticles: possible solution to the problem of surgically induced intracranial contrast enhancement in intraoperative MR imaging.

BACKGROUND AND PURPOSE: Intraoperative MR imaging is increasingly being used to control the extent of surgical resection; however, surgical manipulation itself causes intracranial contrast enhancement, which is a source of error. Our purpose was to investigate the potential of monocrystalline iron oxide nanoparticles (MIONs) to solve this problem in an animal model. METHODS: In male Wistar rats, surgical lesions of the brain were produced. The animals underwent MR examination immediately afterward. In the first group, a paramagnetic contrast agent was administered, whereas the second group of animals received MIONs 1 day before surgery. In a third group of animals, malignant glioma cells were stereotactically implanted in the caudoputamen. Two weeks later, MIONs were IV injected and the tumor was (partially) resected. Immediately after resection, MR examination was performed to determine the extent of residual tumor. RESULTS: Surgically induced intracranial contrast enhancement was seen in all animals in which a paramagnetic contrast agent was used. Conversely, when MIONs had been injected, no signal changes that could be confused with residual tumor were detected. In the animals that had undergone (partial) resection of experimental gliomas, MR assessment of residual tumor was possible without any interfering surgically induced phenomena. CONCLUSION: Because MIONs are stored in malignant brain tumor cells longer than they circulate in the blood, their use offers a promising strategy to avoid surgically induced intracranial contrast enhancement, which is known to be a potential source of error in intraoperative MR imaging.

Animals↗
PubMed2000

MR contrast agents in acute experimental cerebral ischemia: potential adverse impacts on neurologic outcome and infarction size.

The purpose of the study was to investigate the effects of magnetic resonance (MR) contrast agents on neurologic outcome and infarction size in a rat stroke model. Focal cerebral ischemia was induced in 80 rats using an endovascular occlusion technique of the middle cerebral artery. Four hours after occlusion, 64 animals (4 groups of 16 each) received gadodiamide (Gd-DTPA-BMA) in a single (0.1 mmol/kg) or triple (0.3 mmol/kg) clinical dose or the ultrasmall superparamagnetic iron oxide particles contrast agent NC 100150 in a single (0.03 mmol/kg, 1.5 mg Fe(2+)/kg) or double (0.06 mmol/kg, 3.0 mg Fe(2+)/kg) clinical dose, respectively. Sixteen animals received equivolumetric saline (control group). Neurologic score and body weight were recorded every 8 hours. Twenty-four hours after vessel occlusion, infarction size was measured by 2,3, 5-triphenyl-tetrazolium-chloride (TTC) staining. Neither the normal nor the triple clinical dose of gadodiamide or NC 100150 in the single or double dose had any statistically significant effects on infarction volume, mortality, body weight, or neurologic outcome (P > 0.05). Our results suggest that bolus injection of gadodiamide and the ultrasmall superparamagnetic iron oxide particles NC 100150 in clinically relevant doses does not significantly affect infarction volume and clinical outcome of acute cerebral ischemia.

Animals↗
PubMed2000

The benefit of neuronavigation for neurosurgery analyzed by its impact on glioblastoma surgery.

Neuronavigation, today a routine method in neurosurgery, has not yet been systematically assessed in direct comparison with conventional microsurgical techniques. The aim of the present study was the direct comparison of the impact of neuronavigation on glioblastoma surgery regarding time consumption, extent of tumor removal and survival. For each of 52 patients operated for primary glioblastoma with neuronavigation, a patient operated on without navigation was matched. Completeness of tumor resection, including volumetric analysis, was examined by early post-operative MRI. Operating and survival times were obtained for all patients. At a rate of 86.5%, surgeons' opinions about neuronavigation were positive. Operating times were identical in the two groups, while preparation times were 30.4 min longer with navigation. Radiological radicality was achieved in 31% of navigation cases vs. 19% in conventional operations. The absolute and relative residual tumor volumes were significantly lower with neuronavigation. Radical tumor resection was associated with a highly significant prolongation in survival (median 18.3 vs. 10.3 months, p < 0.0001). Survival was longer in patients operated on using neuronavigation (median 13.4 vs. 11.1 months). Neuronavigation increases radicality in glioblastoma resection without prolonging operating time. Regarding the problem of brain shift, neuronavigation should be optimized by intraoperative real-time imaging.

Adult↗
PubMed2000

Clinical evaluation and follow-up results for intraoperative magnetic resonance imaging in neurosurgery.

OBJECTIVE: The use of intraoperative magnetic resonance imaging (MRI) in neurosurgery has increased rapidly, and a variety of concepts have recently been presented. Although the feasibility of the procedure has been demonstrated repeatedly, no conclusive analysis of its effects on the surgical procedures, the extent of tumor removal, and outcomes, or its possible problems, has been performed. METHODS: Of 242 operations performed with intraoperative MRI, 97 procedures for supratentorial glioma treatment were analyzed with respect to intraoperative imaging results and postoperative outcomes. Analysis of the images included assessment of imaging artifacts, image quality, and extent of tumor removal. Patients were monitored to determine radiological progression, survival times, postoperative complications, and morbidity rates. RESULTS: No intraoperative complications related to the imaging procedure were observed. Image quality was good or fair in 85.5% of the cases. Different types of surgically induced imaging changes could be identified. In 56 cases, resection was continued using navigation with intraoperative MRI data sets (rereferencing accuracy, 0.9 mm). For high-grade gliomas, the percentage of cases in which residual tumor was identified by MRI could be significantly reduced from 62% intraoperatively to 33% postoperatively, which was paralleled by a significant increase in survival times for patients without residual tumor. Complication and morbidity rates were within the ranges reported for other studies. CONCLUSION: Intraoperative MRI is safe and allows reliable updating of neuronavigational data, with compensation for brain shifting. Surgically induced imaging changes, which have been identified as a possible problem with intraoperative MRI in general, necessitated comparisons with preoperative scans and require future attention. The extent of tumor removal and survival times were increased significantly. Overall, patients seemed to benefit from the method.

Adolescent↗
PubMed2000

Acute disseminated encephalomyelitis after parenteral therapy with herbal extracts: a report of two cases.

Two patients with acute disseminated encephalomyelitis after repeated injection of extracts from several different plants are described. There was no evidence of prior infection or vaccination. Both patients recovered rapidly after treatment with methylprednisolone. Acute disseminated encephalomyelitis should be considered a rare complication of parenteral therapy with herbal extracts.

Adult↗
PubMed1999

Arterial gas embolism after decompression: correlation with right-to-left shunting.

Paradoxical gas embolism is a possible cause of neurologic sequelae after decompression in divers. The authors detected arterial bubbles after decompression from chamber dives in two of six divers using transcranial Doppler sonography (TCD). Arterial bubbles correlated with the size of right-to-left shunting as diagnosed by contrast TCD. The pathway of spontaneous paradoxical embolism was tracked for the first time, supporting the concept of paradoxical gas embolism as a cause of early neurologic sequelae after decompression in at-risk divers.

Adult↗