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Biomedical subjects

D G Thomas

Publications and source records attributed to D G Thomas.

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

Interactive image-guided neuroendoscopy: development and early clinical experience.

Technical advances and pioneering surgeons have established neuroendoscopy as an accepted diagnostic and therapeutic tool. The clinical indications for endoscopy, variety of operative techniques and number of endoscopic surgeons continue to increase steadily. However, there are fundamental limits to the scope of freehand endoscopy principally governed by the need for direct vision of anatomical and pathological structures. In addition, whilst the expert neuroendoscopist is only occasionally disorientated by complex distorted anatomy, the rising number of novices are likely to be mislead relatively often. We report the integration of neuroendoscopy with an optical neuronavigation system to provide interactive image-guided neuroendoscopy. This combination both removes the constraining requirement for direct vision and provides accurate localisation to guide the surgeon during surgery. We describe the clinical application of this method to two cases where image-guided endoscopy was essential to the safe completion of the procedure.

Adult↗
PubMed1998

A study of medial pallidotomy for Parkinson's disease: clinical outcome, MRI location and complications.

We have studied the effects of unilateral ventral medial pallidotomy in 26 patients with medically intractable Parkinson's disease with marked drug-induced dyskinesias. Preoperatively, all patients were assessed during one 5-day admission according to the Core Assessment Programme for Intracerebral Transplantation (CAPIT) protocol, including rating in the 'practically defined off' and 'best on' states before and during a single-dose levodopa challenge. Motor performance was assessed with subset categories of the Unified Parkinson's Disease Rating Scale (UPDRS), timed motor tests and a standard dyskinesia rating scale. Pallidotomy was performed under stereotaxic CT guidance with intra-operative extracellular microelectrode recording made from the basal ganglia. All patients were re-assessed 3 months postoperatively and a subgroup (n = 9) have so far also been re-assessed after 1 year. Pre- and postoperative performance scores were compared in order to determine which categories of performance improved postoperatively. Significance was accepted at P < 0.005 in order to take into account the multiple number of comparisons performed. Patient medication was compared pre- and postoperatively and the morbidity associated with surgery was also recorded. The most significant improvement postoperatively was the diminution of 'on' dyskinesias contralaterally (67%, P = 0.0001); however, ipsilateral (45%, P = 0.0006) and axial (50%, P = 0.0008) dyskinesias also improved. Contralateral to pallidotomy, the median 'off' motor UPDRS score improved by 27% (P = 0.001) and a significant improvement was also observed in contralateral rigidity by 25% (P = 0.001). There were trends towards improvement in contralateral tremor (33%, P = 0.016) and bradykinesia (24%, P = 0.013) scores. Ipsilateral rigidity improved by 22% (P = 0.005), but other ipsilateral motor scores did not alter significantly. The 'off' gait/postural instability score and 'off' walking time showed marginally significant improvements by 7% (P = 0.007) and 29% (P = 0.014), respectively. On medication, no significant postoperative improvements in parkinsonism were detected. Anti-parkinsonian medication increased by 11% postoperatively. In the subgroup who were available for assessment 1 year postoperatively, responses were generally maintained. Two (7.7%) of the 26 patients had fatal complications (one cerebral haemorrhage and one haemorrhagic infarct) directly related to surgery. Among the remaining 24 patients, four (15.4% of the total 26) had major complications (two persisting and two transient). Ten patients (38.5%) had minor complications. The majority of the complications (major and minor) occurred in the earlier operated patients and the complication rate subsequently declined with increasing operative experience. The remaining 10 patients (38.5%) had no significant side-effects. One of these 10 patients died from an incidental malignant glioma 6 months postoperatively. These findings confirm that levodopa-induced dyskinesias are dramatically reduced following ventral medial pallidotomy and constitute the principal indication for pallidotomy. Improvements in underlying parkinsonism were of smaller magnitude. Pallidotomy may also offer some patients an opportunity to increase antiparkinsonian medication. Patient selection for medial pallidotomy should, therefore, be based largely on anticipated improvements in levodopa-induced dyskinesias, but this must be balanced against the associated morbidity and mortality.

Aged↗
PubMed1998

Neoplasms.

Explore the source record for details and available documents.

Brain Neoplasms↗
PubMed1998

The EASI project--improving the effectiveness and quality of image-guided surgery.

In recent years, advances in computer technology and a significant increase in the accuracy of medical imaging have made it possible to develop systems that can assist the clinician in diagnosis, planning, and treatment. This paper deals with an area that is generally referred to as computer-assisted surgery, image-directed surgery, or image-guided surgery. We report the research, development, and clinical validation performed since January 1996 in the European Applications in Surgical Interventions (EASI) project, which is funded by the European Commission in their "4th Framework Telematics Applications for Health" program. The goal of this project is the improvement of the effectiveness and quality of image-guided neurosurgery of the brain and image-guided vascular surgery of abdominal aortic aneurysms, while at the same time reducing patient risks and overall cost. We have developed advanced prototype systems for preoperative surgical planning and intraoperative surgical navigation, and we have extensively clinically validated these systems. The prototype systems and the clinical validation results are described in this paper.

Quality of Health Care↗
PubMed1998

Postimaging brain distortion: magnitude, correlates, and impact on neuronavigation.

OBJECT: This prospective study was conducted to quantify brain shifts during open cranial surgery, to determine correlations between these shifts and image characteristics, and to assess the impact of postimaging brain distortion on neuronavigation. METHODS: During 48 operations, movements of the cortex on opening, the deep tumor margin, and the cortex at completion were measured relative to the preoperative image position with the aid of an image-guidance system. Bone surface offset was used to assess system accuracy and correct for registration errors. Preoperative images were examined for the presence of edema and to determine tumor volume, midline shift, and depth of the lesion below the skin surface. Results were analyzed for all cases together and separately for four tumor groups: 13 meningiomas, 18 gliomas, 11 nonglial intraaxial lesions, and six skull base lesions. For all 48 cases the mean shift of the cortex after dural opening was 4.6 mm, shift of the deep tumor margin was 5.1 mm, and shift of the cortex at completion was 6.7 mm. Each tumor group displayed unique patterns of shift, with significantly greater shift at depth in meningiomas than gliomas (p = 0.007) and significantly less shift in skull base cases than other groups (p = 0.003). Whereas the preoperative image characteristics correlating with shift of the cortex on opening were the presence of edema and depth of the tumor below skin surface, predictors of shift at depth were the presence of edema, the lesion volume, midline shift, and magnitude of shift of the cortex on opening. CONCLUSIONS: This study quantified intraoperative brain distortion, determined the different behavior of tumors in four pathological groups, and identified preoperative predictors of shift with which the reliability of neuronavigation may be estimated.

Adolescent↗
PubMed1998

Malignant meningioma of the oculomotor nerve without dural attachment. Case report and review of the literature.

Meningiomas, thought to arise from arachnoid cap cells, are usually attached to the dura. Malignancy is present in approximately 1% of these tumors. The authors report the case of a patient with a malignant meningioma arising from the oculomotor nerve with no dural attachment. The patient presented with a 7-month history of left-sided ptosis and diplopia. Magnetic resonance imaging demonstrated an extrinsic mass compressing the root of the oculomotor nerve at its exit from the midbrain. During surgery, a left-sided subtemporal approach revealed the tumor to be arising from the oculomotor nerve. Histological investigation showed a malignant spindle cell lesion with an immunohistochemical profile that was consistent with malignant meningioma. To the authors' knowledge, this is the first documented case of a malignant meningioma arising from the oculomotor nerve.

Adult↗
PubMed1997

Pretreatment prediction of the chemotherapeutic response of human glioma cell cultures using nuclear magnetic resonance spectroscopy and artificial neural networks.

Both tumor metabolism and its response to cytotoxic drugs are intrinsic properties of tumor cells. It is therefore likely that there is a relationship between the two properties, however subtle and complex, wherein the metabolic characteristics of tumor cells can reflect the inherent response (resistance or sensitivity) of these cells to cytotoxic drugs. We used artificial neural network analysis to show that it is possible to distinguish, prior to treatment, between drug-resistant and drug-sensitive human glioma cell cultures from their metabolic profiles, as given by high-resolution proton nuclear magnetic resonance spectra of the cell extracts, and to predict their cellular response to the chemotherapeutic drug 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea in vitro. The results suggest that neural network analysis of tumor nuclear magnetic resonance spectra has potential as a prognostic tool for determining treatment of gliomas, ultimately noninvasively, and may be used to provide information about the metabolic pathways involved in drug response that may be helpful in developing novel treatments for these tumors.

Antineoplastic Agents, Alkylating↗
PubMed1997

Craniopharyngioma: improving outcome by early recognition and treatment of acute complications.

PURPOSE: To assess the frequency, mode of presentation, treatment, and outcome of acute complications in patients with craniopharyngioma around the time of radiotherapy. METHODS AND MATERIALS: A review was made of 188 patients with craniopharyngioma treated with conservative surgery and external beam radiotherapy at the Royal Marsden Hospital between 1950 and 1992. RESULTS: Twenty six (14%) (95% confidence interval: 9-19%) patients with craniopharyngioma developed acute deterioration immediately before, during and 2 months after radiotherapy with visual deterioration (19 patients), hydrocephalus (7 patients), and global deficit (7 patients). Cystic enlargement with or without hydrocephalus was the most common cause of deterioration. No patient or disease characteristics were predictive of deterioration on univariate or multivariate analysis. Eighteen patients had surgical intervention at the time of deterioration and survived the immediate period. Six of seven patients who did not have surgical intervention died. All patients who survived the postcomplication period completed the full course of external beam radiotherapy. The 10-year progression-free survival of 162 patients without deterioration was 86%, and of 18 patients with acute deterioration who recovered after surgery, 77%. CONCLUSION: Patients with craniopharyngioma develop acute deterioration around the time of radiotherapy owing to cystic enlargement and/or hydrocephalus which does not represent tumor progression. Early recognition and appropriate surgical treatment followed by conventional full-dose radiotherapy are associated with good long-term outcome.

Adolescent↗
PubMed1997

Stereotactic thalamotomy in tremor-dominant Parkinson's disease: an H2(15)O PET motor activation study.

Stereotactic thalamotomy is an effective treatment for severe drug-resistant tremor. The thalamus, however, facilitates motor activity, and thalamotomy would be predicted to inhibit movement-associated cortical activation. Two tremulous parkinsonian patients were studied with H2(15)O positron emission tomography before and after left ventralis intermedius thalamotomy. Subjects were scanned at rest and during performance of externally paced joystick movements in freely selected directions with the right hand. Thalamotomy relieved tremor but, as predicted, led to decreased activation of the left sensorimotor cortex, lateral premotor cortex, and parietal area 7 on hand movement.

Aged↗
PubMed1997

Sellar tuberculoma: report of two cases.

Hypophyseal tuberculomas are exceptionally rare. We report two patients with sellar tuberculoma but with no evidence of concurrent extrasellar disease. Although the lesion is often mistaken for adenoma, there are characteristic radiological features: intense enhancement on contrast CT and thickening of the pituitary stalk on MRI in 86% of cases. Accurate diagnosis is important because pituitary tuberculoma is curable.

Adult↗
PubMed1997

Max_r: an optimal method for the selection of subsets of foods for the measurement of specific nutrient exposures.

Max_r, a new method of food subset selection for the measurement of specific nutrient exposures, is programmed. Frequently, epidemiologic questionnaires are designed to measure several individual level exposures, including exposure to one or more nutrients. Although most nutrients are contained in a large number of foods, constraints on questionnaire size allow inclusion of only a subset of these. When nutrient exposure as measured in a subset of foods will be used to estimate the effect of the nutrient on disease risk with a logistic regression model, max_r is the optimal method of choosing the subset. Various aspects of the program are illustrated with a numerical example measuring dietary protein intake. The executable version of this Fortran program for IBM compatible PCs requires 3Mb of memory. It is available (along with complete documentation, test data and output) via e-mail from thomasd@epndce.nci.nih.gov or upon submission of a diskette formatted for MS-DOS.

Dietary Proteins↗
PubMed1997

Heterogeneity of chemosensitivity in six clonal cell lines derived from a spontaneous murine astrocytoma and its relationship to genotypic and phenotypic characteristics.

Heterogeneity in drug sensitivity must, in part, account for the relative lack of success with single agent chemotherapy for glioblastoma multiforme (GBM). In order to develop in vitro model systems to investigate this, clones derived from the VM spontaneous murine astrocytoma have been characterised with regard to drug sensitivity. Six clonal cell lines have been tested for sensitivity to a panel of cytotoxic drugs using an intermediate duration 35S-methionine uptake assay. These lines have previously been extensively characterised with regard to morphological, antigenic, kinetic, tumourigenic potential in syngeneic animals and chromosomal properties and display considerable heterogeneity. The present study indicates that heterogeneity extends to sensitivity to all classes of cytotoxic drugs. The greatest difference in sensitivity between the clones was seen in response to cell cycle-specific drugs like the Vinca alkaloids (14-fold and 20-fold for vincristine (VCR) and vindesine (VIND) respectively), while the nitrosoureas, CCNU and BCNU displayed a smaller fold difference in sensitivity (4.3 and 3.6-fold difference respectively). All the clones were considerably more resistant to the adriamycin (ADM), cis-platinum (C-PLAT) and the Vinca alkaloids than the parental cell line although the difference in sensitivity between the clones and parental cell line were less marked for the nitrosoureas and procarbazine (PCB). It has also been possible to examine the relationship between drug sensitivity and the phenotypic and genotypic properties of these clonal cell lines. There is a relationship between chromosome number and sensitivity of a wide variety of cytotoxic drugs including the nitrosoureas, Vinca alkaloids, PCB, C-PLAT, BLEO but not ADR or 5-FU. Clones with small numbers of chromosomes were more resistant than clones with gross polyploidy. Similarly, sensitivity to Vinca alkaloids and ADM, but not other classes of drugs, was greatest in cells with numerous cytoplasmic processes and which did not express large amounts of cell surface fibronectin. Preliminary experiments have been conducted on reconstituting clonal mixtures of cells with different sensitivity to Vinca alkaloids and results from these studies indicate that the drug resistance phenotype is dominant, with clonal mixtures of sensitive and resistant cell adopting the sensitivity of the more resistant partner. These cell lines should prove to be useful models for examining the cell biological basis of drug resistance in glioma and may lead to the identification and exploitation of novel cellular targets in new therapies for GBM.

Animals↗
PubMed1997

The female tetraplegic: an admission of urological failure.

OBJECTIVE: To present the long-term follow-up of female patients with tetraplegia managed in our unit, many of who require permanent indwelling catheters or urinary diversions that lead to significant complications and associated morbidity. PATIENTS AND METHODS: Eighty-four female tetraplegics (mean age 31 years, range 13-81) were followed for a mean of 9 years (range 2-30). Three groups of patients were identified, depending on their neurology; 27 patients had complete lesions (Frankel A), 20 had incomplete lesions with poor functional recovery (Frankel B/C) and 37 had incomplete lesions with good function (Frankel D/E). RESULTS: The patients with complete lesions (Frankel A) were difficult to manage, with 23 of the 27 (85%) treated using indwelling catheters. Three patients underwent diversion and for one patient, the carer performs clean intermittent catheterization (CIC). Of the 20 patients with Frankel B/C lesions, 14 have permanent indwelling catheters, three are able to perform CIC and three void by controlled triggering of detrusor contractions (reflex voiding). The 37 patients with Frankel D/E lesions fared better and only three (8%) require permanent catheters. Of the others, four (11%) use CIC (one following a cystoplasty) and most (30, 81%) use reflex voiding. Most of the 40 patients with permanent catheters had significant problems with bladder stones (55%), leakage and by-passing (35%), and recurrent symptomatic infections (33%). Patients performing CIC fared better, with most needing anticholinergic therapy or subtrigonal phenol; patients who used reflex voiding also needed these two treatments at some stage. Four patients (two with ileal loops and two with indwelling catheters) developed dilated upper tracts. CONCLUSIONS: The urological status of female patients following cervical cord injury depends on the level of injury and recovery. Most patients with Frankel A-C lesions have permanent indwelling catheters and most patients with Frankel D or E lesions void with controlled triggering or use CIC. Although upper tract dilation was seen in only 5%, patients had significant morbidity related to the bladder.

Adolescent↗
PubMed1997

Supravesical diversion for incontinence: a long-term follow-up.

OBJECTIVES: To report the long-term follow-up of patients with an ileal conduit urinary diversion, constructed for intractable incontinence in patients with benign disease where the native bladder was left in situ, and to determine the fate of the bladder and the effects on the upper tracts. PATIENTS AND METHODS: Ninety-three patients (mean age at operation 50 years, range 8-78) were followed for a minimum of 2 (mean 5) years after undergoing an ileal conduit urinary diversion. Seventy-one patients (76%) had neurological disease (18 traumatic and 53 non-traumatic) and the single largest group of patients (28) suffered from disseminated sclerosis. Twenty-two patients with no obvious neurological disease underwent the procedure for unmanageable incontinence or intractable bladder symptoms or for interstitial cystitis. The patients were assessed for problems in the bladder remnant, stomal problems and upper tract changes following surgery. RESULTS: Forty-eight patients (52%) had recurrent vesical infections and pyocystis and of these, 23 (48%) required admission for in-patient bladder irrigations. To control recurrent bladder problems, five patients required creation of a vesico-vaginal fistula; this did not suffice in two and they subsequently underwent cystectomy; in total, five patients underwent cystectomy. Twenty-nine patients (31%) had stomal problems, those with the skin being commonest. Parastomal hernia repair was required in 10 (10%) patients and three had further surgery for recurrence. Of 83 patients with normal upper tracts before diversion, post-operative radiological assessment showed upper tract dilatation in 28 (34%) and in 10 (12%) this was bilateral. In one patient with a neuropathic bladder, the ileal diversion resulted regression of the dilated upper tracts. CONCLUSIONS: Supravesical diversion is safe and well tolerated but assessing the long-term follow-up, the incidence of bladder problems in over half these patients and upper tract changes in over a third suggests an indefinite follow-up is mandatory. Despite these problems, most patients are delighted with the outcome of their surgery.

Adolescent↗
PubMed1997

Bowel problems after enterocystoplasty.

OBJECTIVES: To document the changes in bowel habit in patients who have undergone enterocystoplasty. PATIENTS AND METHODS: Sixty-nine patients with neuropathic (NP) and 44 with non-neuropathic (NNP) bladder dysfunction (mean age 26 years, range 13-61, 93.6% socially continent), followed for at least 36 months after cystoplasty, were assessed using a questionnaire addressing faecal frequency, consistency, method of evacuation and incontinence episodes before and after surgery. RESULTS: Of the patients with NP bladder dysfunction, 26 (38%) had more and seven (10%) less frequent bowel action after surgery, with 36 (52%) unchanged; 38 (55%) of patients had unchanged consistency, 26 (38%) were looser and five (7%) more constipated; 41 (59%) opened their bowels as before, 16 (23%) needed more help and 12 (17%) less help to evacuate; 16 (23%) patients had more and 17 (25%) less episodes of incontinence; 21 (30%) patients felt their bowels had not become normal after their operation and only 24 (35%) that they had returned to normal within 3 months of their operation. The bowel segment used was ileum in 44 patients, ileocaecal in 11 and sigmoid cystoplasty in 14. Patients with intact ileum did not have the same degree of diarrhoea, with only three of the 14 patients with a sigmoid cystoplasty being adversely affected. Of the patients with NNP bladder dysfunction, 18 patients (41%) had a more and five (11%) a less frequent bowel action; 20 (46%) had more loose and five (11%) less loose bowel action; similar numbers (five and four) needed either an increase or a decrease in laxatives or enemata: surprisingly, 12 patients (27%) felt they had an increase in the episodes of incontinence; 17 (39%) patients felt their bowels returned to normal within 3 months of surgery and 30% felt their bowels had not become normal after surgery. Only one patient in this group had a sigmoid cystoplasty and she did not find that the operation interfered with her bowel function. CONCLUSIONS: Ileal resection results in malabsorption of bile acids, maldigestion of fat and an imbalance of water and electrolytes. Patients with neurogenic bladders are finely balanced between acceptable bowel function and choas, and surgery often tips this balance the wrong way. In 30% of the present patients, bowel problems persisted after surgery, with 38% having increased frequency. 38% having looser consistency and 23% more incontinence episodes following surgery. More surprisingly, a high percentage of NNP patients had bowel problems after cystoplasty.

Adolescent↗
PubMed1997

Pallidotomy in Parkinson's disease increases supplementary motor area and prefrontal activation during performance of volitional movements an H2(15)O PET study.

Supplementary motor area and right dorsal prefrontal cortex activation in Parkinson's disease is selectively impaired during volitional limb movements. Since posteroventral pallidotomy improves motor performance in Parkinson's disease patients 'off' medication (i.e. off medication for 9-12 h), we hypothesized that it would also concomitantly increase supplementary motor area and dorsal prefrontal cortex activation. Six Parkinson's disease patients with a median total motor Unified Parkinson's Disease Rating Scale (UPDRS) of 52.5 (range 34-66) 'off' medication underwent unilateral right posteroventral pallidotomy. The patients had H2(15)O PET when 'off' medication before and 3-4 months after surgery. Each PET study comprised four to six measurements of regional cerebral blood flow either at rest or while performing regularly paced joystick movements in freely selected directions (forward, backward, left or right) using the left hand. Pre- and postoperative scans were performed in an identical manner and the associated levels of activation were compared using statistical parametric mapping. After pallidotomy, the median total motor UPDRS score 'off' medication decreased by 34.7% (P = 0.03) and mean response times of joystick movements following the pacing tones improved by 13.8% (P = 0.08). Relative increases in activation of the supplementary motor area and right dorsal prefrontal cortex were observed during joystick movements (P < 0.001). Decreased activation was seen in the region of the right pallidum (P = 0.001). We conclude that pallidotomy reduces pallidal inhibition of thalamocortical circuits and reverses, at least partially, the impairment of supplementary motor area and dorsal prefrontal cortex activation associated with Parkinson's disease.

Adult↗