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Biomedical subjects

P David

Publications and source records attributed to P David.

At least 19 recordsLinked to original sources
PubMed2006

[Ruptured mesenteric aneurysm from Listeria monocytogenes].

Infections due to Listeria monocytogenes usually occur in pregnant women, in elderly or immunocompromised patients. We report the case of an immunosuppressed woman who had been hospitalized for a meningoencephalitis due to L. monocytogenes. She was operated on for an abdominal hemorrhagic shock due to a ruptured mycotic aneurysm of the inferior mesenteric artery. Arterial aneurysms due to this germ are rare and occur on large arteries. Only 17 cases have been previously described in the literature and just one concerning a mesenteric artery.

Aortic Dissection↗
PubMed2006

[Cohort KBP-2000-CPHG: Evaluation of factors influencing survival in lung cancer].

INTRODUCTION: Lung cancer continues to have a poor prognosis despite some therapeutic advances. BACKGROUND: The last fifteen years has seen a dramatic increase in the incidence of lung cancer in women and an increased proportion of adenocarcinomas in both sexes. A study of overall survival as a function of gender and other prognostic factors has been established using the cohort of patients from the study KBP-2000-CPHG. METHODS: KBP-2000-CPHG is an epidemiological study carried out throughout the year 2000 looking at histologically confirmed primary lung cancers managed in general hospitals. 5,667 patients have been included. The study of survival looks at 2 and 5-year outcomes. The date and cause of death are recorded for each patient. In the absence of these data the date of the last contact is noted. If this is less than 4 months the patient is considered to be alive. If more than four months have elapsed a graduated strategy for establishing vital status is pursued which involves reviewing records from various different sources. RESULTS AWAITED: A preliminary review of the data was undertaken between September 2004 and March 2005 which obtained data on 5 567 patients. The analysis of survival according to sex and other forecast prognostic factors is underway.

Adenocarcinoma↗
PubMed2006

Microsatellites reveal extensive geographical, ecological and genetic contacts between invasive and indigenous whitefly biotypes in an insular environment.

Human-mediated bioinvasions provide the opportunity to study the early stages of contact between formerly allopatric, divergent populations of a species. However, when invasive and resident populations are morphologically similar, it may be very difficult to assess their distribution in the field, as well as the extent of ecological overlap and genetic exchanges between invasive and resident populations. We here illustrate the use of data obtained from a set of eight microsatellite markers together with Bayesian clustering methods to document invasions in a group of major tropical pests, Bemisia tabaci, which comprises several morphologically indistinguishable biotypes with different agronomic impacts. We focus on the island of La Réunion, where an invasive biotype (B) has recently been introduced and now interacts with the resident biotype (Ms). The temporal and spatial distribution, host-plant range and genetic structure of both biotypes are investigated. We showed (i) that, without prior information, clustering methods separate two groups of individuals that can safely be identified as the B and Ms biotypes; (ii) that the B biotype has invaded all regions of the island, and showed no signs of genetic founder effect relative to the Ms biotype; (iii) that the B and Ms biotypes coexist in sympatry throughout most of their geographical ranges, although they tend to segregate into different host plants; and finally (iv) that asymmetrical and locus-specific introgression occurs between the two biotypes when they are in syntopy.

Animals↗
PubMed2006

Coexistence in a metacommunity: the competition-colonization trade-off is not dead.

The competition-colonization trade-off model is often used to explain the coexistence of species. Yet its applicability has been severely criticized, mainly because the original model assumed a strict competitive hierarchy of species and did not allow for any preemptive effect. We considered the impact of relaxing both of these limitations on coexistence. Relaxing trade-off intensity makes coexistence less likely and introduces a minimum colonization rate below which any coexistence is impossible. Allowing for preemption introduces a limit to dissimilarity between species. Surprisingly, preemption does not impede coexistence as one could presume from previous studies, but can actually increase the likelihood of coexistence. Its effect on coexistence depends on whether or not species in the regional pool are strongly limited in their colonization ability. Preemption is predicted to favour coexistence when: (i) species are not strongly limited in their colonization ability; and (ii) the competitive trade-off is not infinitely intense.

Animals↗
PubMed2005

11C-methionine PET for the diagnosis and management of recurrent pituitary adenomas.

PURPOSE: The detection of recurrent pituitary adenoma by magnetic resonance imaging (MRI) is rendered uncertain by the tissue remodelling that follows surgery or radiotherapy. We aimed to evaluate the contribution of PET with 11C-methionine (MET-PET) in the detection and management of recurrent pituitary adenoma. METHODS: Thirty-three patients with pituitary adenoma were evaluated postoperatively by MET-PET, either because of biological evidence of active residual tumour or because of MRI demonstration of non-functional adenoma growth. We studied 24 secreting adenomas and nine non-functional adenomas. RESULTS: In 30 patients, MET-PET detected abnormally hypermetabolic tissue. In 14 out of these, MRI did not differentiate between residual tumour and scar formation. In nine of these 14 cases, major therapeutic decisions were undertaken (radiosurgery and surgery). In another group of 16 patients, both MET-PET and MRI detected abnormal tissue. In one case, neither MRI nor MET-PET detected adenomatous tissue. Finally, abnormal tissue was detected in two patients on MRI solely. In these two cases, failure of MET-PET to reveal the adenoma was attributable to concomitant inhibitory therapy. The sensitivity of MET-PET and MRI varied as a function of the tumour type: all non-functional adenomas were localised by both modalities, while MET-PET detected all adrenocorticotropic hormone-secreting adenomas whereas MRI depicted only one of these eight lesions. Fifteen out of 17 patients treated by radiosurgery showed clinical improvement after treatment. CONCLUSION: We suggest that MET-PET is a sensitive technique complementary to MRI for the detection of residual or recurrent pituitary adenomas. It should gain a place in the efficient management of these tumours.

Adult↗
PubMed2005

Functional MRI activation of somatosensory and motor cortices in a hand-grafted patient with early clinical sensorimotor recovery.

The aim of this study was to investigate somatosensory and motor cortical activity with functional MRI (fMRI) in a hand-grafted patient with early clinical recovery. The patient had motor fMRI examinations before transplantation, and motor and passive tactile stimulations after surgery. His normal hand and a normal group were studied for comparison. A patient with complete brachial plexus palsy was studied to assess the lack of a fMRI signal in somatosensory areas in the case of total axonal disconnection. Stimulating the grafted hand revealed significant activation in the contralateral somatosensory cortical areas in all fMRI examinations. The activation was seen as early as 10 days after surgery; this effect cannot be explained by the known physiological mechanisms of nerve regeneration. Although an imagination effect cannot be excluded, the objective clinical recovery of sensory function led us to formulate the hypothesis that a connection to the somatosensory cortex was rapidly established. Additional cases and fundamental studies are needed to assess this hypothesis, but several observations were compatible with this explanation. Before surgery, imaginary motion of the amputated hand produced less intense responses than executed movements of the intact hand, whereas the normal activation pattern for right-handed subjects was found after surgery, in agreement with the good clinical motor recovery.

Adult↗
PubMed2005

[Imaging in paediatric epilepsy].

Epilepsy is a chronic disease, often with an onset during childhood and characterized by spontaneous and recurrent seizures. It concerns 0.5-1% of children under 16 years of age. A classification proposed by the International League Against Epilepsy (ILEA) in 2001 takes into account recent genetic factors involved in epilepsy and attenuates the sharp demarcation between generalized and partial seizures. This classification tends to define whether imaging is indicated or not. Imaging is useless in simple cases of fits associated with hyperthermia and in benign idiopathic epilepsy. It is debated if it is a first episode of epilepsy without a particular context and no neurological signs. In all other cases of epilepsy in children, imaging is indicated. In descending order of frequency the possible causes include malformations (as abnormal gyral development and phakomatoses), hypoxic-ischemic lesions, non-accidental injuries, infections, metabolic diseases and tumors. Being much more sensitive than computed tomography (CT), magnetic resonance imaging (MRI) is the technique of choice to identify an underlying cause in symptomatic epilepsy. Clinical data are mandatory in order to direct a proper MRI investigation. The recently developed diffusion-weighted sequence is particularly useful in the acute phase of certain events such as hypoxia-ischemia, trauma and metabolic disease. CT scan is used in emergency situations and also as a complement to MRI for example to identify calcified lesions. In this way, imaging contributes to establish the nature and define the extension of epileptogenic lesions, thereby guiding therapeutic management. MRI also allows follow-up of the consequences of repeated seizures (such as mesial temporal sclerosis and selective neuronal necrosis) on the cerebral parenchyma and plays a role in the establishment of a prognosis.

Adolescent↗
PubMed2005

Apparent diffusion coefficient (ADC) and magnetization transfer ratio (MTR) in pediatric hypoxic-ischemic brain injury.

BACKGROUND AND PURPOSE: a review of the literature reveals the increasing interest in using Diffusion magnetic resonance imaging, with diffusion weighted images (DWI) and ADC (Apparent Diffusion Coefficient) quantitation, in pediatric hypoxic-ischemic brain injury. However, ADC and MTR (Magnetization Transfer Ratio) as quantitative tools have not been investigated together in these pathological conditions in young pediatric patients. The aim of this study was to apply a quantitative method by using ADC and MTR calculation in order to propose a reproducible quantitation of brain parenchymal lesions. METHODS: we conducted a prospective study including all children presenting with suspected cerebral hypoxic-ischemic injury. 15 children were included, among them 10 males and 5 females aged from 36 weeks of gestation to 17 months with a median age of 10,5 months. All MR examinations were performed at 1.5 Tesla unit including conventional MR (T1, T2 and Inversion-recovery sequences) and DWI with ADC map. ADC and MTR ROI (region of interest) measurements were made, in the frontal subcortical and periventricular white matter (WM) as well as in the gray matter (GM=basal ganglia), and in focal lesions. RESULTS: ADC and MTR values were abnormal in focal lesions and in diffuse injury with no evidence of lesion on conventional MRI and DWI. We observed a strong inverse correlation between these ADC and MTR (R=0,66 in WM; R=0,61 in GM). CONCLUSION: ADC and MTR calculation may be helpful as a reproductive method to quantify the lesions and detect diffuse lesions in hypoxic-ischemic pediatric brain injury.

Diffusion Magnetic Resonance Imaging↗
PubMed2005

[Von Hippel-Lindau disease: recent advances in genetics and clinical management].

Von Hippel-Lindau (VHL) disease is a hereditary cancer syndrome that predisposes to the development of a panel of highly vascularized tumors including CNS and retinal hemangioblastomas, endolymphatic sac tumors, clear-cell renal cell carcinomas (RCC), pheochromocytomas and pancreatic neuroendocrine tumors. CNS hemangioblastomas and RCC are the two main life-threatening manifestations. The disease is caused by germline mutations in the VHL tumor-suppressor gene that plays a major role in regulating the oxygen-sensing pathway by targeting the hypoxia-inducible factor HIF for degradation in proteasome. Somatic inactivation of the VHL gene occurs also in most sporadic RCC and sporadic CNS hemangioblastomas. The demonstration of the critical role of VHL in angiogenesis is paving the way for the development of new specific drugs that could represent an attractive potential treatment for VHL but also for sporadic RCC and other cancers.

Humans↗
PubMed2005

Biological invasions: the case of planorbid snails.

A large number of planorbid snails are now commonly transported by man mainly through the aquatic plant trade. However, only a restricted number of species establish viable populations in a new habitat and a more restricted number spread. Only five planorbid species can be ranked in this last category and can be considered as pests because of their role in the transmission of parasites to humans or domestic animals: Biomphalaria glabrata, B. straminea, B. tenagophila, B. pfeifferi and Indoplanorbis exustus. The neotropical B. glabrata, B. straminea and B. tenagophila have proven their capacity to invade another continent sometimes creating new transmission foci. The African B. pfeifferi and the Indian I. exustus have also expanded their distribution area with long-distance dispersal. Other planorbid species, i.e. Helisoma duryi, Amerianna carinata and Gyraulus spp. have been able to establish viable populations, but not to spread, presumably because they are limited to specific habitats or/and display poor competitive abilities.

Animals↗
PubMed2005

Hybridization and invasiveness in the freshwater snail Melanoides tuberculata: hybrid vigour is more important than increase in genetic variance.

Many invasive taxa are hybrids, but how hybridization boosts the invasive process remains poorly known. We address this question in the clonal freshwater snail Melanoides tuberculata from Martinique, using three parental and two hybrid lines. We combine an extensive field survey (1990-2003) and a quantitative genetic experiment to show that hybrid lines have outcompeted their parents in natural habitats, and that this increased invasiveness co-occurred with pronounced shifts in life-history traits, such as growth, fecundity and juvenile size. Given the little time between hybrid creation and sampling, and the moderate standing genetic variance for life-history traits in hybrids, we show that some of the observed trait changes between parents and hybrids were unlikely to arise only by continuous selection. We therefore suggest that a large part of hybrid advantage stems from immediate heterosis upon hybridization.

Analysis of Variance↗
PubMed2005

[Homocysteine, folic acid, group B vitamins and cardiovascular risk].

Although there is a high degree of proof relating plasma homocysteine levels to cardiovascular risk, the role of homocysteine as a causal cardiovascular risk factor remains controversial. Prospective long-term clinical trials in high cardiovascular risk populations usually show a positive relationship between plasma homocysteine and the degree of cardiovascular risk. However, shorter term studies and/or those carried out in populations with lower cardiovascular risk show either a weaker correlation or no relationship at all. To date no study has shown proof of the reversibility of cardiovascular risk due to hyperhomocysteinaemia; nevertheless, a number of studies using intermediate criteria support the hypothesis of a benefit due to reduction of plasma homocysteine levels. A number of therapeutic trials published with clinical criteria have not shown convincing results in either direction. A number of interventional trials are underway: notably the SUFOLOM 3 trial in France, and the question of a benefit on cardiovascular risk by reducing homocysteine levels should be answered in the next few years. In the meantime, with the exception of homocysteinuria in which therapeutic strategies have shown their efficacy in the reduction of atherothrombotic risk with high levels of proof, the authors do not recommend the treatment of mild hyperhomocysteinaemia in any clinical setting other than "clinical trials" and certain "compassionate" indications such as early and/or recurrent vascular events associated with hyperhomocysteinaemia in the absence of conventional risk factors.

Cardiovascular Diseases↗
PubMed2004

Understanding the relationship between the inbreeding coefficient and multilocus heterozygosity: theoretical expectations and empirical data.

Geneticists have been interested in inbreeding and inbreeding depression since the time of Darwin. Two alternative approaches that can be used to measure how inbred an individual is involve the use of pedigree records to estimate inbreeding coefficients or molecular markers to measure multilocus heterozygosity. However, the relationship between inbreeding coefficient and heterozygosity has only rarely been investigated. In this paper, a framework to predict the relationship between the two variables is presented. In addition, microsatellite genotypes at 138 loci spanning all 26 autosomes of the sheep genome were used to investigate the relationship between inbreeding coefficient and multilocus heterozygosity. Multilocus heterozygosity was only weakly correlated with inbreeding coefficient, and heterozygosity was not positively correlated between markers more often than expected by chance. Inbreeding coefficient, but not multilocus heterozygosity, detected evidence of inbreeding depression for morphological traits. The relevance of these findings to the causes of heterozygosity--fitness correlations is discussed and predictions for other wild and captive populations are presented.

Animals↗
PubMed2004

[Stereotactic mapping for radiosurgical treatment of vestibular schwannomas].

RATIONALE: As an exclusively image-guided surgery method, radiosurgery requires special attention in the choice of imaging modalities and acquisition parameters must be set with extreme care. METHODS: Quality control for resolution and accuracy of computed tomography (CT) scanners must be performed. Magnetic resonance imaging (MRI) distortions should be limited through magnetic field homogeneity adjustment (shimming) and acquisition parameters optimization. These inaccuracies should then be quantified through systematic combination of MRI and CT in the radiosurgery planning system. MRI pulse sequences selection criteria are defined by their ability to delineate tumor contrast enhancement and to image cranial nerves and vessels relative arrangement in the cistern and canal. Topography of the petrous structures, such as cochlea, vestibulum and facial nerve canal should be visible. Exact definition of real extension of the lesion at the end of the canal may require specific technical solutions. These technical requirements must be balanced depending on the lesion Volume staging (Koos), the treatment history (microsurgery), the clinical condition (hearing quality), the pathological context (NF2) or the age of the patient. RESULTS: T1-weighted Volumetric MRI pulse sequences (3D-T1) show a contrast enhanced signal that is useful for both the pons interface delineation in Koos III cases, and the canal ending in Ohata A and B. On the other hand, 3D-T1 introduce inaccuracies from magnetic susceptibility distortions and partial Volume effects. High resolution CISS T2-weighted Volumetric pulse sequences (3D-T2) give superior stereotaxic definition attributable to their better resolution (half a millimeter) minimizing partial Volume effects and to their lower magnetic susceptibility minimizing distortions. 3D-T2 allows direct nerve visualization. Moreover, this pulse sequence with contrast injection, show improved distinction between the pons and the nerves due to signal differences within the schwannomas. Fat saturation pulse sequences are of interest in post-microsurgery conditions. CONCLUSIONS: Radiology phase quality is critical and its complexity requires a high commitment to obtain satisfactory clinical results. Solelt the 3D-T1 MRI modality seems to us not to comply to minimum security criteria.

Diffusion Magnetic Resonance Imaging↗
PubMed2004

[Imaging for stereotaxic treatment of vestibular schwannomas. Error factors and corrections].

BACKGROUND AND PURPOSE: Gamma Knife radiosurgery treatment of vestibular schwannomas requires high accuracy for the prescribed dose definition and delivery. The main factors contributing to the error are the anatomical distortions of imaging modalities used for treatment planning. Imaging limitations and error factors are reviewed and detailed. Multimodality rationale for the delineation of vestibular schwannomas and surrounding structures are assessed. Quality control strategies are discussed and a distortion correction technique using a radiological phantom is presented. METHODS: Computed tomography is considered as the reference for spatial accuracy after appropriate scanner quality control using the stereotaxic fiducials system. Magnetic resonance imaging pulse sequence distortions are measured with a phantom designed for 3D non-linear local distortion evidence. A distortion correction transformation is computed from the phantom images and applied to the patient images. Results are verified using the stereotaxic fiducials system. RESULTS: Fiducials registration errors show spatial accuracy improvement, approaching computed tomography quality, after distortion correction of magnetic resonance images. CONCLUSIONS: The multimodal imaging approach for the dose planning of vestibular schwannomas radiosurgery treatment is relevant. Quality control of spatial accuracy for imaging modalities is mandatory and realistic in clinical routine.

Ear Neoplasms↗
PubMed2004

[In vivo evaluation of tumor response to radiosurgery: application to vestibular schwannomas].

Imaging follow-up of vestibular schwannomas (VS), such as CT or MR, does not allow assessing the response of the tumor tIssue to radiosurgery. Changes in contrast enhancement are frequently observed, with a loss of contrast enhancement within the treated VS. However, this typical aspect does not anticipate the long-term success of radiosurgery for VS. New functional and metabolic image modalities could be useful to assess in vivo radiosurgery-induced tIssue changes. Such data already exist, using techniques such as MR spectroscopy, positron emission tomography (PET) and SPECT, but they concern almost exclusively the evaluation of primary SNC tumors and metastases of systemic cancers. There are, however, very sparse metabolic and functional data concerning the in vivo evaluation of the response of the tumor tIssue to radiosurgery. Moreover, such information is only anecdotal in VS. In other disorders, PET and MR spectroscopy data suggest interesting new directions for the assessment of radiosurgery follow-up. Based on the predictive information provided by PET and MR spectroscopy in primary CNS tumors, it would be worthwhile to design a prospective study evaluating the role of these imaging modalities for in vivo assessment of radiosurgery-treated SV.

Brain↗