Biomedical subjects

J Valk

Publications and source records attributed to J Valk.

At least 91 records · Page 5Linked to original sources

PubMed1993

[Acute psychosis in a patient with a combination of sickle cell disease and hemoglobin-C disease].

A 35-year-old negroid patient, known to have sickle cell-haemoglobin C disease, after heavy exercise developed an acute thrombotic crisis localised mainly in the brain. The clinical manifestations were those of an acute psychosis with severe confusion, aggressiveness, unco-operative behaviour and incontinence for faeces and urine. With adequate therapy he recovered after a few days. This so-called cerebral sickle cell crisis, confirmed by multiple small encephalomalacia lesions on the MRI which are typical of this disease, is a rare complication and difficult to diagnose.

Acute Disease↗

PubMed1993

Nontriggered magnetic resonance velocity measurement of the time-average of pulsatile velocity.

The feasibility of the determination of the time-average of pulsatile velocity obtained via a nontriggered magnetic resonance (MR) acquisition is studied. The advantage of this method, in comparison with a triggered acquisition, is a considerable reduction (approximately 15x) in acquisition time. However, pulsatility causes image artifacts, known as ghosts, and the Fourier transform technique required for the imaging procedure accomplishes time-averaging of the complex MR signal. Both effects can result in errors in the velocity determined. Calculations show that these errors depend on the velocity time function and the acquisition parameters. In vivo comparison of triggered and nontriggered MR velocity measurements in the femoral artery of volunteers (n = 7) shows larger statistical and systematic errors in the latter, which depend on the excitation angle. Therefore, this nontriggered average velocity measurement is only useful as a fast and rough estimation of the time-averaged velocity.

Blood Flow Velocity↗

PubMed1993

Embryonic development of the mammalian caudal neural tube.

In the literature, some controversy still exists about the embryonic developmental processes involved in the formation of the caudal neural tube. Therefore, a three-dimensional and histological study concerning the normal development of the caudal neural tube was performed on both mouse and human embryos. Three developmental processes can be distinguished in caudal neural tube development: caudal neuropore closure, secondary neurulation, and degeneration and differentiation of the secondary neural tube. Caudal neuropore closure occurs at the level of somite 32-34 in both species. Therefore, primary neurulation leads to the formation of all spinal cord segments and ganglia. Secondary neurulation involves cell deposition from a cluster of neurectodermal cells at the caudal end of the closed neural tube, directly around a lumen, the lumen always in contact with the lumen of the primary neural tube. This process leads only to the formation of the primordia of the filum terminale and ventriculus terminalis and, possibly, part of the conus medullaris. Secondary neurulation is followed by a period characterized by degeneration and differentiation of the secondary neural tube. Its lumen and neural tissue will disappear, whereas part of the secondary neurectodermal cells differentiate to a fibrous layer comparable and continuous with the marginal layer of the primary neural tube. This fibrous layer represents the future filum terminale. The embryological processes indicated above can be helpful in the interpretation of congenital anomalies affecting the caudal spinal cord and spine.

Animals↗

PubMed1993

Mycotic encephalitis: predilection for grey matter.

In mycotic infections of the brain three patterns of abnormality may be observed: meningitis, granuloma, and encephalitis. The first two, consisting of diffuse meningeal enhancement and mass lesion respectively, can easily be visualised by CT or MRI, but are nonspecific. The third pattern has been described histopathologically; as the clinical picture is nonspecific and the diagnosis is often unsuspected, especially in immunocompetent patients, acquaintance with the characteristic CT and MRI patterns of mycotic encephalitis may help in establishing the correct diagnosis, with important therapeutic consequences.

Adult↗

PubMed1993

A double-blind, comparative study of gadodiamide injection and gadopentetate dimeglumine in MRI of the central nervous system.

Seventy-nine patients with known or suspected central nervous system lesions were studied with MRI in a phase III double-blind study. Forty were given gadopentetate dimeglumine (Gd-DTPA) and 39 gadodiamide injection (Gd-DTPA BMA), a new low-osmolar nonionic contrast enhancing medium. The dosage was 0.1 mmol/kg body weight, corresponding to 0.2 ml/kg. Spin-echo sequences were performed before and immediately after injection. The safety and efficacy of the two contrast media were assessed. No changes were observed in blood pressure, heart rate or neurological status. Five adverse effects (two episodes of headaches, two of nausea and one of dizziness) were reported by 2 patients who received gadodiamide injection and 1 who received gadopentetate dimeglumine. All events were mild and their relationship to the contrast media was uncertain. For both contrast media statistically significant changes in serum iron were observed 24 h after injection. More than 70% of the patients had abnormal findings on MRI, and in 56% of these contrast enhancement of the abnormal structure or lesion was seen. Contrast enhancement provided the diagnosis in about 50%, changed it in 40% and increased diagnostic confidence in 95%.

Adult↗

PubMed1993

L-2-hydroxyglutaric acidaemia: clinical and biochemical findings in 12 patients and preliminary report on L-2-hydroxyacid dehydrogenase.

L-2-Hydroxyglutaric acidaemia represents a newly defined inborn error of metabolism, with increased levels of L-2-hydroxyglutaric acid in urine, plasma and cerebrospinal fluid. The concentration in cerebrospinal fluid is higher than in plasma. The other consistent biochemical finding is an increase of lysine in blood and cerebrospinal fluid, but lysine loading does not increase L-2-hydroxyglutaric acid concentration in plasma. This autosomal recessively inherited disease is expressed as progressive ataxia, mental deficiency with subcortical leukoencephalopathy and cerebellar atrophy on magnetic resonance imaging. Since these features were described in 8 patients by Barth and co-workers in 1992, 4 more patients with similar findings have been diagnosed and added to the present series. L-2-Hydroxyglutaric acid is found in only trace amounts on routine gas chromatographic screening in normal persons, and its origin, its fate and even its relevance to normal metabolism are unknown. Therefore its catabolism was studied in normal liver. Incubation of rat liver with L-2-hydroxyglutaric acid did not produce H2O2, which excluded (peroxisomal) L-2-hydroxyacid oxidase as the main route of catabolism. However, L-2-hydroxyglutaric acid is rapidly dehydrogenated if NAD+ is added as a co-factor to the standard reaction medium. This could also be demonstrated in human liver. The preliminary evidence for this enzyme activity in rats and humans, L-2-hydroxyglutaric acid dehydrogenase, is given. Further investigations are required to clarify the possible relevance to the metabolic defect in L-2-hydroxyglutaric acidaemia.

Adolescent↗

PubMed1993

The role of magnetic resonance in the evaluation of functional results after CABG/PTCA.

Magnetic resonance imaging (MRI) is a non-invasive modality which can be used for direct visualization of coronary artery bypass grafts. Spin-echo and gradient-echo (cine-MRI) techniques are now available on standard MR machines and provide information on graft morphology and graft patency with a 90% accuracy. By combining the standard techniques with MR phase velocity mapping, the flow rate in the graft can be measured, thereby offering a unique non-invasive assessment of the graft function. Newer techniques include MR coronary angiography, pharmacologically induced stress MRI, ultrafast MRI of the first-pass (perfusion) of a paramagnetic contrast agent through the myocardium, and 31P MR spectroscopy of high-energy phosphate metabolism of the myocardium. All of these may develop into valuable diagnostic tools for the assessment of functional results after CABG or PTCA, but still require clinical validation. At present, MRI is a useful screening procedure for assessment of graft patency and function in post-operative pain syndromes and in late graft occlusion or stenosis.

Angioplasty, Balloon, Coronary↗

PubMed1993

A semiquantative rating scale for the assessment of signal hyperintensities on magnetic resonance imaging.

Differences in grading signal hyperintensities on magnetic resonance imaging may explain earlier reported conflicting results in studies of normal aging and dementia. We designed a new rating scale in which periventricular and white matter signal hyperintensities as well as basal ganglia and infratentorial signal hyperintensities are rated separately in a semiquantative way. In this study we compared the inter- and intra-observer agreements of this scale to the widely used rating scale of Fazekas. We confirmed the poor to reasonable intra- and inter-observer agreements of the Fazekas scale. The new scale, although more elaborate, provided good agreements with respect to the white matter, basal ganglia and infratentorial signal hyperintensities. In rating periventricular hyperintensities this scale yielded no advantage. It is concluded that this scale may be of use in studies especially focussing on deep white matter pathology on MRI, because it provides more detailed information, with good intra- and inter-observer reliability.

Aged↗

PubMed1993

Cortical laminar abnormalities--occurrence and clinical significance.

Cortical laminar necrosis is a histopathological entity, related to conditions of cerebral energy depletion. Clinical correlates are supposed to be spastic motor deficits, decreased intellectual capacity and epilepsy. A study was performed in 45 children with cortical laminar abnormalities in signal intensity on MRI. The purpose of the study was to evaluate causes and clinical consequences of these cortical abnormalities on MRI in order to find indirect evidence for the hypothesis that they may represent cortical laminar necrosis. In view of the frequently present concomitant white matter damage, two contrast groups were formed: one group of 40 children with periventricular white matter abnormalities, part of them with subcortical extensions of the white matter damage; and another group of 53 children without abnormalities on MRI. Data concerning history, present clinical condition and final diagnosis were collected. The presence of cortical laminar abnormalities on MRI was found to be strongly associated with a history of cerebral energy depletion, especially hypoxia-ischemia, either in the perinatal period or later in life. Whereas white matter abnormalities tended to be more frequent in premature children, cortical laminar abnormalities tended to occur more frequently in term neonates and older children. The presence of cortical laminar abnormalities on MRI was correlated with an increased risk of spasticity in children without concomitant white matter abnormalities. In children with white matter lesions, cortical laminar abnormalities did not contribute to the risk of spasticity, which was already highly increased by the presence of white matter damage. No association was found between cortical abnormalities on MRI and epilepsy or psychomotor retardation.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Diseases↗

PubMed1993

A case of macrocephaly, hydrocephalus, megacerebellum, white matter abnormalities and Rosenthal fibres.

The authors report the case of a young boy with macrocephaly, cerebellar symptoms and signs of raised intracranial pressure. Magnetic resonance imaging showed obstruction of the aqueduct, ventricular enlargement of the cerebellum and areas of increased signal intensity in the cerebellar and frontal white matter. A stereotactic biopsy of the cerebellum showed many Rosenthal fibres and glial proliferation. Although the histopathological and neuroradiological findings were suggestive of Alexander's disease, the initial presentation and clinical course were unusual for this diagnosis. The authors suggest that a separate form of Alexander's disease should be distinguished with predominant clinical, neuroradiological and neuropathological cerebellar involvement. This form also seems to have a better life-expectancy.

Abnormalities, Multiple↗

PubMed1992

[Progressive multifocal leukoencephalopathy in AIDS].

This study was carried out to determine clinical features, abnormalities on CT scan and MRI, and course in patients with HIV-I-related progressive multifocal leukoencephalopathy (PML). There were 14 patients with a presumptive diagnosis of PML among 500 HIV-I infected patients with neurological complaints, examined between September 1982 and May 1991 in the University Medical Centre in Amsterdam by a neurologist. In these 14 patients clinical features, imaging abnormalities and course of the disease were analysed retrospectively. All patients presented with progressive focal neurological abnormalities. Cerebrospinal fluid analysis revealed aspecific abnormalities in 5/13 patients. CT scanning of the brain showed hypodense areas in the white matter, without mass effect and with contrast enhancing in only one patient. MR Imaging of the brain showed high signal intensity areas in white matter and in gray matter (10/13), without mass effect, and with contrast enhancement in two. Specimens for neuropathological examination were obtained from 7 patients; in all these cases the diagnosis of PML was confirmed. In patients with AIDS a presumptive diagnosis of PML can be based on clinical features, brain imaging abnormalities and course. However neuropathological confirmation remains the gold standard. Usually the course in these patients was steadily progressive. Most patients died within one year.

Acquired Immunodeficiency Syndrome↗

PubMed1992

1H and 31P magnetic resonance spectroscopy of the brain in degenerative cerebral disorders.

Proton and phosphorus magnetic resonance spectroscopy of the brain was performed in 35 patients with degenerative cerebral disorders: 24 patients had demyelinating (white matter) disorders and 11 patients had neuronal (gray matter) disorders. Four grades of demyelination and three grades of cerebral atrophy were distinguished by magnetic resonance imaging criteria. The spectroscopic data were compared with normal values previously obtained. With increasing degrees of demyelination, lower ratios of phosphodiesters to beta-ATP were found. This trend was statistically significant. Decreased phosphodiester-beta-ATP ratios occurred simultaneously with imaging abnormalities. The decrease in phosphodiester-beta-ATP ratio in demyelinated areas is attributed to white matter rarefaction. Increasing cerebral atrophy was accompanied by lower ratios of N-acetyl aspartate to creatine. This trend was statistically significant. The decrease in the N-acetyl aspartate-creatine ratio was demonstrated before the magnetic resonance images showed signs of cerebral atrophy in patients with neuronal disorders. As N-acetyl aspartate is located exclusively in neurons and their branches, a decrease of the N-acetyl aspartate-creatine ratio can be attributed to neuronal and axonal damage and loss.

Adult↗

PubMed1992

L-2-hydroxyglutaric acidemia: a novel inherited neurometabolic disease.

Routine screening for organic acids revealed increased and isolated urinary excretion of L-2-hydroxyglutaric acid in 8 mentally retarded patients from five unrelated families, including three pairs of siblings. L-2-Hydroxyglutaric acid concentration was also found to be increased in the cerebrospinal fluid (CSF) and to a lesser extent in plasma. The only other biochemical abnormality was an increased concentration of lysine, both in plasma and in CSF. No organic acid abnormality was found on screening of asymptomatic family members. Patients were of either sex, and became symptomatic during childhood, with moderate to severe mental deficiency in all and definite cerebellar dysfunction in 7. Magnetic resonance imaging revealed an identical abnormal pattern with subcortical leukoencephalopathy, cerebellar atrophy, and signal changes in the putamina and dentate nuclei, in all patients. No specific biochemical function or catabolic pathway involving L-2-hydroxyglutaric acid is known in mammals, including humans. Preliminary loading and dietary studies failed to reveal the origin of the compound. The elevated CSF/plasma ratio suggests that it is in part generated within the central nervous system. This report describes a novel inherited neurometabolic disease, probably autosomal recessive, with distinct clinical, biochemical, and neuroimaging features.

Adolescent↗

PubMed1992

Analysis of phospholipids in brain tissue by 31P NMR at different compositions of the solvent system chloroform-methanol-water.

Brain phospholipids can be quantitated by high-resolution 31P NMR of crude brain tissue extracts in the solvent system chloroform-methanol-water (+EDTA) which was introduced recently (P. Meneses and T. Glonek, J. Lipid Res. 29, 679 (1988)). Phospholipid resonance positions depend on the type of tissue extract and on solvent composition. The effects of systematic variation of the solvent system on phospholipid NMR profiles are presented. Resolution can be optimized by adjustment of the solvent composition. Virtually all phospholipid classes can be resolved, and the major phospholipids in brain: sphingomyelin and phosphatidyl-choline, -serine, -inositol, -ethanolamine, and -ethanolamine plasmalogen can be quantitated easily. Additional resonances have been assigned to phosphatidylcholine plasmalogen, alkylacyl-phosphatidylcholine and phosphatidylinositolbisphosphate. NMR offers a rapid method for quantitative analysis of the phospholipid composition in brain tissue which requires minimum sample handling.

Aged↗

PubMed1992

MR imaging of skeletal metastases from medulloblastoma.

The findings of MR imaging in 3 patients with bone metastases from medulloblastoma are reported. The first patient showed focal lesions of low signal intensity on T1-weighted spin echo images at a time when bone scintigraphy was negative for metastases. This patient later developed extensive osteosclerotic lesions visible on plain films. The bone marrow of the second patient showed diffuse low signal intensity on T1-weighted images. After chemotherapy the signal intensity of the bone marrow increased which correlated with a return of normal hematopoietic tissue. A response to chemotherapy was also found on MR imaging and repeat bone marrow biopsies in a third patient. A consistent finding was a low signal intensity on pre-gadolinium images, but the pattern (focal or diffuse abnormal signal intensity) was different in each patient. To our knowledge, this is the first report on MR imaging findings in bone metastases from medulloblastoma.

Acetabulum↗

PubMed1992

White matter lesions on magnetic resonance imaging in clinically diagnosed Alzheimer's disease. Evidence for heterogeneity.

In a prospective magnetic resonance imaging (MRI) study we evaluated the prevalence and severity of white matter changes in 29 patients with Alzheimer's Disease (AD) and 24 age-matched healthy elderly, all without cerebrovascular risk factors. The AD patients were divided into two groups according to age at onset of symptoms, one with presenile onset AD (n = 13) and one with senile onset AD (n = 16), who were matched for dementia severity. Signal hyperintensities were rated using a semiquantitative scoring method, separately in the periventricular region (PVH) and in the lobar white matter (WMH), as well as in the basal ganglia (BGH) and in the infratentorial region (ITFH). Cortical atrophy as a parameter of grey matter involvement was rated on a 0 (absent) to 3 (severe) scale. We found PVH, WMH and BGH scores to be significantly higher in senile onset AD patients than in age-matched controls. By means of multiple linear logistic regression we found that PVH, WMH and BGH scores were significantly dependent on the diagnosis of senile onset AD, while the PVH score also showed a significant age dependency. Cortical atrophy did not differ significantly between presenile onset AD and senile onset AD patients. These results indicate that presenile onset AD and senile onset AD patients differ with respect to white matter involvement, but not with respect to grey matter involvement on MRI. Since cerebrovascular risk factors were excluded these findings may indicate that senile onset AD patients display more small vessel involvement (arteriolosclerosis) than presenile onset AD patients, suggesting additional (microvascular) factors for the dementia syndrome in senile onset AD. Our data lend support to the growing body of evidence that AD is heterogeneous, consisting of at least two types. Based on our findings two forms can be distinguished: (i) a 'pure' form of the disease, usually with early disease onset, and no more white matter changes than normal for age; (ii) a 'mixed' form, usually with disease onset later in life, and showing more white matter changes on MRI than normal for age.

Aged↗

PubMed1992

Atrophy of medial temporal lobes on MRI in "probable" Alzheimer's disease and normal ageing: diagnostic value and neuropsychological correlates.

Magnetic resonance imaging (MRI) has shown a great reduction in medial temporal lobe and hippocampal volume of patients with Alzheimer's disease as compared to controls. Quantitative volumetric measurements are not yet available for routine clinical use. We investigated whether visual assessment of medial temporal lobe atrophy (MTA) on plain MRI films could distinguish patients with Alzheimer's disease (n = 21) from age matched controls (n = 21). The degree of MTA was ascertained with a ranking procedure and validated by linear measurements of the medial temporal lobe including the hippocampal formation and surrounding spaces occupied by cerebrospinal fluid. Patients with Alzheimer's disease showed a significantly higher degree of subjectively assessed MTA than controls (p = 0.0005). Linear measurements correlated highly with subjective assessment of MTA and also showed significant differences between groups. Ventricular indices did not differ significantly between groups. In Alzheimer's disease patients the degree of MTA correlated significantly with scores on the mini-mental state examination and memory tests, but poorly with mental speed tests. This study shows that MTA may be assessed quickly and easily with plain MRI films. MTA shown on MRI strongly supports the clinical diagnosis of Alzheimer's disease, is related to memory function, and seems to occur earlier in the disease process than does generalised brain atrophy.

Aged↗

PubMed1992

Global left ventricular perfusion: noninvasive measurement with cine MR imaging and phase velocity mapping of coronary venous outflow.

Velocity and volumetric flow of left ventricular venous outflow in the distal coronary sinus were measured with magnetic resonance (MR) velocity mapping techniques in 24 healthy men. A total of 16-21 velocity maps were acquired throughout the cardiac cycle. To determine the accuracy of the MR velocity-mapping pulse sequence, measurements were obtained with a flow phantom. Mean blood flow was 144 mL/min +/- 62 (standard deviation); mean velocity, 2.1 cm/sec +/- 1.0; and mean cross-sectional area, 1.2 cm2. Phasic measurements revealed a biphasic flow pattern in the coronary sinus, with a first peak in systole (257 mL/min +/- 174) and a second peak in early diastole (1,090 mL/min +/- 487). The cross-sectional area varied between 0.5 cm2 +/- 0.2 at end diastole and 1.9 cm2 +/- 0.6 in systole, a finding that suggests a capacitance function for venous outflow. Mean blood flow measurements were in agreement with measurements obtained invasively in previous studies. It is concluded that MR velocity mapping can enable noninvasive measurement of coronary venous outflow and global left ventricular perfusion and may become clinically useful in assessment of coronary blood flow reserve.

Adult↗