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Biomedical subjects

D G Thomas

Publications and source records attributed to D G Thomas.

At least 73 records · Page 4Linked to original sources
PubMed1997

Neuronavigation--impact on operating time.

It is uncertain whether the use of image-guided surgery has an influence on operating time. We prospectively studied the time requirements which have to be invested for using image-guided surgery and performed a comparison of operating room times from 125 matched pairs of image-guided and conventional operations. Our study revealed that neuronavigation has to be regarded as time neutral in general neurosurgery, whereas in stereotactic surgery, namely biopsy retrival, a significant reduction of anaesthetic time can be achieved through the complete separation of imaging and operation in the frameless approach.

Anesthesia↗
PubMed1997

Surgical treatment of patients with single and dual pathology: relevance of lesion and of hippocampal atrophy to seizure outcome.

Modern neuroimaging can disclose epileptogenic lesions in many patients with partial epilepsy and, at times, display the coexistence of hippocampal atrophy in addition to an extrahippocampal lesion (dual pathology). We studied the postoperative seizure outcome of 64 patients with lesional epilepsy (median follow-up, 30 months) and considered separately the surgical results in the 51 patients with a single lesion and in the 13 who had dual pathology. In patients with a single lesion, 85% were seizure free or significantly improved (Engel's class I-II) when the lesion was totally removed compared with only 40% when there was incomplete resection (p < 0.007). All three patients with dual pathology who had both the lesion and the atrophic hippocampus removed became seizure free. In contrast, only 2 of the 10 patients with dual pathology undergoing surgery aimed at the lesion or at the hippocampus alone became seizure free (p < 0.05), although 4 of them showed significant improvement (Engel's class II). We conclude that the outcome in patients with single epileptogenic lesions is usually dependent upon the completeness of lesion resection. In patients with dual pathology, surgery should, if possible, include resection of both the lesion and the atrophic hippocampus.

Adolescent↗
PubMed1997

Clinical introduction of an adjustable rigid instrument holder for frameless stereotactic interventions.

Interactive image guidance is now in routine use for open neurosurgical procedures and has demonstrated patient benefits. However, freehand interactive guidance is not an appropriate replacement for the traditional frame-based stereotactic procedures of biopsy, electrode placement, and functional lesioning. These point-based procedures require precise target localization and direct instrument guidance to avoid collateral brain injury. To perform true frameless stereotactic procedures requires a guide that is also adjustable for positioning, lockable, and adaptable to multiple instruments. We describe such a device, which is employed for the guidance of biopsy needles, shunts, electrodes, and endoscopes during neuronavigation. The method of frameless stereotactic biopsy retrieval with an infrared-based neuronavigation system is described, clinical results are given, and further areas of application discussed.

Adult↗
PubMed1996

A randomized trial on dose-response in radiation therapy of low-grade cerebral glioma: European Organization for Research and Treatment of Cancer (EORTC) Study 22844.

PURPOSE: Cerebral low-grade gliomas (LGG) in adults are mostly composed of astrocytomas, oligodendrogliomas, and mixed oligoastrocytomas. There is at present no consensus in the policy of treatment of these tumors. We sought to determine the efficacy of radiotherapy and the presence of a dose-response relationship for these tumors in two multicentric randomized trials conducted by the European Organization for Research and Treatment of Cancer (EORTC). The dose-response study is the subject of this article. METHODS AND MATERIALS: For the dose-response trial, 379 adult patients with cerebral LGGs were randomized centrally at the EORTC Data Center to receive irradiation postoperatively (or postbiopsy) with either 45 Gy in 5 weeks or 59.4 Gy in 6.6 weeks with quality-controlled radiation therapy. All known parameters with possible influences on prognosis were prospectively recorded. Conventional treatment techniques were recommended. RESULTS: With 343 (91%) eligible and evaluable patients followed up for at least 50 months with a median of 74 months, there is no significant difference in terms of survival (58% for the low-dose arm and 59% for the high-dose arm) or the progression free survival (47% and 50%) between the two arms of the trial. However, this prospective trial has revealed some important facets about the prognostic parameters: The T of the TNM classifications as proposed in the protocol appears to be one of the most important prognostic factors (p < 0.0001) on multivariate analysis. Other prognostic factors, most of which are known, have now been quantified and confirmed in this prospective study. CONCLUSION: The EORTC trial 22844 has not revealed the presence of radiotherapeutic dose-response for patients with LGG for the two dose levels investigated with this conventional setup, but objective prognostic parameters are recognized. The tumor size or T parameter as used in this study appears to be a very important factor.

Adolescent↗
PubMed1996

Measurement of exposure to nutrients: an approach to the selection of informative foods.

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 length permit the inclusion of only a subset of these. In this paper, the authors review the two common methods of food selection, and they propose two new methods. When the intent is to estimate the effect of the nutrient on disease risk using a logistic regression model, the authors show that their Max_r method is optimal. With the use of case-control data, they examine the assumption of non-differential measurement error that is essential to the validity of all analyses that rely on shortened questionnaires. They conclude by combining the statistical considerations developed for judging adequacy of a selection method with their empirical results and suggest new goals for dietary questionnaires and a new approach to questionnaire construction consistent with those goals.

Bias↗
PubMed1996

Subependymoma of the cervical cord.

Subependymomas are benign lesions of the central nervous system. Their occurrence in the spinal cord is rare. It is important to recognize these lesions because their total surgical excision is feasible and leads to long term symptom remission-a case of a spinal subependymomas localized in the cervical region is discussed and a review of the relevant literature is presented.

Glioma, Subependymal↗
PubMed1996

Acquired immune deficiency syndrome (AIDS) and cerebral astrocytoma.

The presence of cerebral lesions in patients affected by the acquired immune deficiency syndrome (AIDS) has been estimated to be around 10%, with the majority being infective lesions or primary central nervous system lymphomas. The co-occurrence of a cerebral glioma in such patients is rare. The aim of this report is to present four more cases, discussing their clinical and neuroradiological features, as well as the outcome and the possible pathogenesis.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Artificial urinary sphincter in patients with neurogenic bladder dysfunction.

OBJECTIVE: To assess the role of the artificial urinary sphincter (AUS) in the management of sphincter weakness incontinence in neuropathic patients. PATIENTS AND METHODS: Ninety patients (75 male and 15 female, mean age 26 years, range 13-62) with neurogenic bladder dysfunction (71 with congenital and 19 with acquired cord lesions) who underwent implantation of an AUS were reviewed. All patients were followed up for a minimum of one year after the initial implantation of the sphincter (mean 4 years, range 1-10). Pre-operative video-urodynamics demonstrated sphincter weakness incontinence in all patients, with 24 patients having an acontractile-type bladder. Of 66 patients with intermediate-type bladders, 52 underwent cystoplasty. RESULTS: Eighty-three patients (92%) were continent both night and day, three were occasionally damp and controlled by pharmacotherapy, and four had a persistent poor result. Of the 66 patients with detrusor hyper-reflexia, 52 (79%) required a cystoplasty to achieve continence and 14 (21%) were controlled with anti-cholinergic therapy. The re-operation rate was 28% (25/90) and complications included six infections, seven erosions, eight system failures, two pump failures, one sheered tube and one rectal and one bladder perforation. Seventy (78%) of the patients currently perform intermittent catheterization to treat high post-voiding residual urine volumes. CONCLUSIONS: A rate of continence > 90% was achieved in these neurogenic patients after implantation of an AUS and we recommend a simultaneous cystoplasty in patients with detrusor overactivity.

Adolescent↗
PubMed1996

Artificial urinary sphincter for post-prostatectomy incontinence.

OBJECTIVE: To assess the role of the artificial urinary sphincter in the management of patients with post-prostatectomy incontinence. PATIENTS AND METHODS: The study comprised 28 patients (mean age 71 years, range 45-81) with post-prostatectomy incontinence caused by sphincter deficiency who underwent implantation of an artificial sphincter and were followed for a mean of 41 months (range 6-79). RESULTS: Twenty-one (75%) patients had a bulbar cuff and seven (25%) had a membranous urethral cuff implanted. Problems with the bulbar urethral cuff included persistent stress leakage in six, system failure in two and infection in one patient. Nine patients with the bulbar urethral cuff and one patient with the membranous urethral cuff required revision. Of the nine re-operations in those fitted with a bulbar urethral cuff, five required a higher pressure balloon, one a smaller cuff, two had system failures replaced and one had a membranous urethral cuff implanted because of infection. Three of these nine patients needed a third operation and in all of these a membranous urethral cuff was inserted. A total of 33 operations were performed in 21 patients with bulbar urethral cuffs (a re-operation rate of 57%) and eight operations were carried out in seven patients with membranous urethral cuffs (a re-operation rate of 14%). Three patients needed anticholinergic therapy and one needed a clam cystoplasty for intractable instability. Twenty-four patients (86%) are dry and fully continent, three (11%) have occasional stress leakage and one patient had a cerebro-vascular accident 9 months after surgery and now has an indwelling catheter. CONCLUSIONS: Patients who had artificial sphincters implanted to treat post-prostatectomy incontinence achieved a social continence rate of 96%. With bulbar urethral sphincters there was a high incidence of post-implantation incontinence and a high re-operation rate to achieve this success.

Aged↗
PubMed1996

Randomized trial of bolus phenylephrine or ephedrine for maintenance of arterial pressure during spinal anaesthesia for Caesarean section.

Thirty-eight healthy women undergoing elective Caesarean section under spinal anaesthesia at term were allocated randomly to receive boluses of either phenylephrine 100 micrograms or ephedrine 5 mg for maintenance of maternal arterial pressure. The indication for administration of vasopressor was a reduction in systolic pressure to < or = 90% of baseline values. Maternal arterial pressure (BP) and heart rate (HR) were measured every minute by automated oscillometry. Cardiac output (CO) was measured by cross-sectional and Doppler echocardiography before and after preloading with 1500 ml Ringer lactate solution and then every 2 min after administration of bupivacaine. Umbilical artery pulsatility index (PI) was measured using Doppler before and after spinal anaesthesia. The median (range) number of boluses of phenylephrine and ephedrine was similar; 6 (1-10) vs 4 (1-8) respectively. Maternal systolic BP and CO changes were similar in both groups, but the mean [95% CI] maximum percentage change in maternal HR was larger in the phenylephrine group (-28.5 [-24.2, -32.9]%) than in the ephedrine group (-14.4 [-10.6, -18.2]%). As a consequence atropine was required in 11/19 women in the phenylephrine group compared with 2/19 in the ephedrine group (P < 0.01). Mean umbilical artery pH [95% CI] was higher in the phenylephrine group (7.29 [7.28-7.30]) than in the ephedrine group (7.27 [7.25-7.28]). The results of the present study support the use of phenylephrine for maintenance of maternal arterial pressure during spinal anaesthesia for elective Caesarean section.

Adult↗
PubMed1996

Craniotomy guidance using a stereo-video-based tracking system.

In open intracranial neurosurgery, it is desirable to minimize exposure and to approach the target in the most accurate way possible. The VISLAN system described here employs a completely passive hand-held locator which is tracked by a video system and does not require a mechanical linkage nor cables. The system also tracks easily recognizable, constant, anatomical landmarks of the patient. By this means the initial registration of pre-operative imaging and the detection of, and correction for, patient movement can be accomplished. High-resolution MRI segmented interactively is used to define external surface and brain anatomy. Thus, a pre-operative patient representation (POPR) is planned. During the surgical procedure the patient's head is illuminated by structured light and stereo-video pictures obtained from two television cameras mounted above the head. The system is calibrated and registered with the POPR using a chamfered matching algorithm. The locator is also tracked in space by the video system, and its tip position shown in relation to the POPR on the video monitor.

Craniotomy↗
PubMed1996

Interstitial cystitis: involvement of the intestine.

Two patients with intractable interstitial cystitis are presented. Both have had substitution enterocystoplasty and in both, unabated symptoms have resulted in ileal loop diversion. In both patients the excised neobladder had shown extensive changes of interstitial cystitis involving all layers, including the muscle layers of the explanted intestine. Also in one of these patients, symptoms suggestive of interstitial cystitis persisted and biopsies taken from the ileal loop have shown histological changes characteristic of interstitial cystitis. The presentation of interstitial cystitis in the intestine is discussed and we conclude that interstitial cystitis does manifest in the intestine.

Cystitis, Interstitial↗
PubMed1996

Assay of anticancer drugs in tissue culture: comparison of a tetrazolium-based assay and a protein binding dye assay in short-term cultures derived from human malignant glioma.

Because of the methodological difficulties associated with the MTT assay in screening short-term cultures derived from human malignant glioma, a chemosensitivity assay based on the protein staining using sulforhodamine B (SRB) has been optimized for use with these cells. SRB at a fixed dye concentration achieved maximal staining density at 20 min for most cell lines and this intensity was not further increased by using dye concentrations above 0.2%. A delay in staining after fixation did not significantly decrease staining intensity, but delay in dye extraction after fixation and staining did. There was an excellent quantitative and qualitative linear relationship between cell number determined by either the SRB assay or by cell counting, but not with the MTT assay which consistently underestimated the number of cells in assay plates. The MTT assay appeared to be incapable of detecting less than about 150 cells/well, while these small numbers of cell were readily detectable by either cell counting or SRB staining. There was a close correlation between chemosensitivity values derived from the MTT and SRB assays for procarbazine, CCNU and vincristine when the endpoint is taken as either the ID25, ID50 or ID75. The results indicate that the SRB is capable of producing broadly similar results to the MTT assay, but is more sensitive in the detection of small numbers of cells with a linear relationship between cell number and SRB staining intensity over a wide range of cell numbers. It is capable of producing data from short-term cultures from malignant glioma and offers technical advantages over the MTT assay in that plates may safely be stored at certain points during the assay without the need for immediate processing. The SRB assay provides a useful alternative to the MTT assay for determining the sensitivity of short-term cultures of human glioma to cytotoxic drugs.

Antineoplastic Agents↗
PubMed1995

Enterocystoplasty in the neuropathic bladder.

Patients with neuropathic bladders who have intractable hyperreflexia often require cystoplasty and in patients adequately motivated and counselled, continence rates in excess of 90% can be achieved. Seventy-eight patients with neurological disease have undergone enterocystoplasty and are presented. Twenty-two patients had acquired cord lesions of which 17 were traumatic. Of the 56 patients with congenital myelodysplasia, 49 were meningomyelocele, 5 had sacral agenesis, and 2 lipoma of cauda equina. The mean age was 26 (range 13-61) years with 48 male and 30 females. Pre-operative video urodynamics showed sphincter weakness in 54 patients, all patients had intermediate type bladders; hyperreflexia in 52, reduced compliance in 17, and in 7 a combination of both. Forty-seven patients had ileal, 20 had sigmoid, and 11 had ileocaecal cystoplasty. Fifty-two patients had an artificial urinary sphincter inserted, 9 had a colposuspension, and 1 had both for concurrent sphincter weakness incontinence. Acceptable continence has been achieved in 73 (93.6%) patients, 65 claiming complete continence with no pads or incontinence episodes and the 8 others needing pharmacotherapy or pads. Two of our 5 failures have been converted to an ileal loop, 2 are awaiting further surgery, and 1 is wet despite normal urodynamics. Our threshold for initiating intermittent catheterisation is low and 63 (81%) of our patients catheterise. Complications in these patients are few and the only one of note is persistent bowel problems in 30% of our patients. Cystoplasty is recommended as safe and reliable in the treatment of neurogenic detrusor over activity with a continence rate of 93% being achieved.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1995

Intravesical oxybutynin in patients with posterior rhizotomies and sacral anterior root stimulators.

This report investigates the use of intravesical oxybutynin in spinal injury patients, who have had dorsal rhizotomies to abolish reflex detrusor activity and void with S2, S3, and S4 stimulation, done with the Brindley anterior root stimulator. Six male patients (age range 27 to 56, mean 36 years) who have had Brindley anterior root stimulators implanted were included in this study. Video urodynamic assessment was done and 10 mg of oxybutynin hydrochloride was instilled through the urethral catheter. This was left in the bladder for 60 minutes and video urodynamics were repeated. Voiding, both pre and post oxybutynin, was achieved with sacral root stimulation. Peak detrusor pressure (Pves) during voiding in the 6 patients before oxybutynin instillation was 89, 154, 90, 60, 56, and 80 (mean 88.2) cm of water. Post oxybutynin the pressures were 83, 163, 95, 40, 30, and 68 (mean 79.8) cm of water. The peak flow rate (Qmax) pre oxybutynin was 32, 24, 20, 20, 12, and 28 (mean 22.7) ml per second and this changed to 28, 31, 18, 24, 10, and 32 (mean 23.8) ml per second. This shows no difference in the detrusor pressure (P = 0.2) and flow rate (P = 0.54) pre and post oxybutynin instillation into the bladder. Effectiveness of oxybutynin is attributed to a combination of M3 receptor antagonism in the smooth muscle and direct spasmolytic, local anaesthetic and calcium channel blocking action. Its therapeutic benefit is limited by the anti cholinergic side effects (40-80%) and recent studies have shown the intravesical route to be effective and better tolerated.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Intravesical↗
PubMed1995

Frameless stereotaxy and interactive neurosurgery with the ISG viewing wand.

Preliminary experience with the ISG wand for frameless stereotaxy is presented. The wand is a multijointed mechanical arm with a range of 25 inch radius sphere. The arm has a analog/digital hybrid transducers to locate the spatial position of the probe tip. The real time displays of triplanar 2D images with an optional 2D/3D image helps in surgical planning and interactive surgery. Seventeen patients underwent neurosurgical procedures with the help of wand. The wand was used to place minimal craniotomies, localise the brain-tumour interface and excise the lesions. The wand had an accuracy of 1.8 mm (SEM +/- 0.36 mm) in localising the lesions. Thus, the use of frameless stereotaxy has made easier and more precise surgical planning in several applications.

Adolescent↗