Biomedical subjects

L Symon

Publications and source records attributed to L Symon.

At least 109 records · Page 6Linked to original sources

PubMed1989

[Extracellular concentration of dopamine and dopamine metabolites in the rat striatum during cerebral ischemia and reperfusion].

Many data suggest that the presence of dopamine (DA) is a prerequisite for the development of neuronal damage in the striatum; neural injury could be initiated by a massive release from dopaminergic nerve terminals during ischemia. The current study was undertaken in order to define the mechanism through which ischemia alters dopaminergic neurotransmission, and to examine the subsequent events early during recirculation. Experiments were performed on 14 male anesthetized Sprague Dawley rats. The ischemic insult consisted of 20 min global cerebral ischemia (4-vessel occlusion) followed by 80 min reperfusion. Cardiac arrest concluded this phase of the experiment, but measurements were continued for 60 min more. Measurements of catechols were made in the striatum using in vivo differential pulse voltammetry (DPV), each 4 min, throughout the experiment and for 60 min post-mortem. DPV data were substantiated with intracerebral dialysis; 20 min dialysate samples were analysed for dopamine (DA) and homovanillic acid (HVA; DA metabolite) using high performance liquid chromatography (HPLC). Repeated in vivo DPV measurements of striatal catechols during ischemia/reperfusion were collected in 11 of 14 experiments. In 6 out of 11 rats, ischemia induced a massive catechols release in the striatum, resulting in a marked increase in extracellular level (350 to 1200% of control), which persisted throughout ischemia. In these rats, a marked rise in extracellular DA was detected in the dialysate sample collected in the contralateral striatum during ischemia, together with a fall in HVA, probably due to ischemic inhibition of the enzymatic oxidation of DA. Catechol was cleared from the extracellular space within minutes of reperfusion, indicating functional catechol uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗

PubMed1988

Assessment of reversible cerebral ischaemia in man: intraoperative monitoring of the somatosensory evoked response.

Central conduction time (CCT) has been monitored in 37 patients undergoing temporary arterial occlusion in aneurysm surgery. 17 patients had internal carotid, 17 had middle cerebral, and 4 had basilar artery occlusion. Internal carotid or middle cerebral artery occlusion lasting less than 12 minutes has not been associated with postoperative morbidity, in any case without appreciable change in CCT after occlusion. Prompt prolongation of CCT was warned the surgeon, but CCT prolongation up to 10 ms could occur without permanent neurological deficit, except in one Grade 4 patient. 10 of 18 patients who lost the N 20 cortical potential showed postoperative neurological deficit, which was promptly recoverable in 7 patients. The speed of loss or recovery of N 20 enabled a patients's prognosis to be predicted. Irrecoverable postoperative deficit is unlikely if the N 20 takes longer than 4 minutes to disappear, to reappears within 20 minutes after recirculation.

Evoked Potentials, Somatosensory↗

PubMed1988

Intraoperative monitoring of the electrocochleogram and the preservation of hearing during acoustic neuroma excision.

We have monitored the electrocochleogram (ECochG) of 24 patients, using a transtympanic electrode, during acoustic neuroma excision. All patients had unilateral tumours with good preoperative hearing and complete excision was achieved in each case. Of the 24 patients, seven retained some hearing, however, a further two patients had normal ECochG waveforms at the end of operation but were nevertheless deaf. Thus, there is not an invariable correlation between immediate preservation of the ECochG and hearing. As expected, tumour size was important in hearing preservation. Five of seven patients with tumours less than 1.5 cm in diameter retained some hearing after operation, whereas 15 of 17 patients with tumours greater than 1.5 cm in diameter were deaf.

Audiometry, Evoked Response↗

PubMed1988

Lhermitte-Duclos disease (dysplastic gangliocytoma): a case report with CT and MRI.

A 31 year old female was admitted with a one month history of left foot drop and diplopia. CT of the posterior fossa revealed gross displacement of the 4th ventricle by a large non-enhancing cerebellar mass but gave no indication of its nature. MRI sequences showed two masses within the left cerebellar hemisphere extending into the vermis and demonstrated a very unusual septation within the lesion. In addition both cerebellar tonsils were displaced below the foramen magnum and there was a syrinx extending from C2 to the conus. At operation a demarcated lesion was excised from the apparently normal surrounding cerebellar tissue and proved histologically to be Lhermitte-Duclos disease. We believe that these are the first diagnostic magnetic resonance images of this condition.

Adult↗

PubMed1988

The effects of acute proximal basilar artery occlusion on the primate cerebral circulation.

The effects of acute proximal basilar artery occlusion on blood flow, autoregulation and CO2 reactivity in four separate regions of the brain (cerebral cortex, thalamus, brainstem and caudal pons) were studied and compared in 30 anaesthetised baboons. Significant flow changes were seen in all areas of the basilar territory, even in instances where the posterior communicating artery was observed to be relatively large. Flow changes were also seen in regions of the brain remote from the basilar territory. Areas furthest from the collateral blood supply showed the largest changes in blood flow, as has previously been shown in the case of proximal middle cerebral artery occlusion. From this, one can predict that in surgery, the more rostral the occlusion of the artery, the safer the procedure should be. At normal blood pressure, while the collateral circulation to the brainstem and thalamus was adequate to maintain normal electrical function after basilar occlusion, the flow was totally inadequate to maintain autoregulation or CO2 reactivity in the basilar territory.

Animals↗

PubMed1988

Changes in pyramidal tract conduction with experimental brain-stem ischaemia in the monkey.

The effect of graded ischaemia on intracranial nerve fibre conduction has not previously been studied quantitatively. We measured pyramidal tract (PT) discharges evoked by electrical stimulation of the ipsilateral motor cortex, together with local blood flow (by hydrogen clearance), in the internal capsule and ventral pons of baboons anaesthetised with alpha-chloralose. Changes in conduction time and amplitude of the motor volley were monitored over this PT segment as it was subjected to progressive ischaemia in controlled stages. Conduction time increased significantly, with attenuation of the volley, at average brain-stem tissue flows below 30 ml/100 g/min. Using paired stimuli, we demonstrated relative refractory and supernormal characteristics of PT conduction. In mild ischaemia, the conduction time of the test response decreased, much more than with single stimulation, and in denser ischaemia it increased, relatively more so at smaller inter-stimulus intervals. The data demonstrate the impairment of conduction in a population of CNS axons with reduced local blood flow and indicate that the transmission of relatively rapid sequences of impulses would be the first aspect of conduction to suffer in ischaemia prior to conduction block.

Animals↗

PubMed1988

Surgical management of acoustic neuromas during the last five years. Part I.

A consecutive series of 94 patients with acoustic neuromas, who were treated in the years 1980-1984, was reviewed. Hearing loss was the most common presenting symptom. During 1980-1984, all acoustic neuromas were treated surgically; 93 cases had a total excision and only one case had a subtotal excision. Mortality and morbidity were low and patients who had a fair to poor outcome rating had large tumors. Overall, cranial nerve VII was preserved in 64.1% of cases, while cranial nerves VII and VIII were anatomically preserved in 27% of cases.

Aged↗

PubMed1988

Surgical management of acoustic neuromas during the last five years. Part II: Results for facial and cochlear nerve function.

Postoperative facial and cochlear nerve function in 83 consecutive patients with acoustic neuromas, who were undergoing their initial surgical procedure during 1980-1984, have been examined. The facial nerve was preserved in anatomic continuity in 71% of cases. Various nerve grafting procedures were used when the facial nerve was divided; the most common of these was a faciohypoglossal anastomosis, which was performed in 20 cases. The facial and cochlear nerves were anatomically preserved in 30.1% of all patients having their initial surgical procedure. Good speech discrimination was preserved in four patients, whereas more crude hearing was preserved in six other patients.

Adolescent↗

PubMed1988

In situ freezing of the brain for metabolic studies: evaluation of the "box" method for large experimental animals.

The box method of freezing the brain in situ was assessed in baboons. The cooling rate of the tissue was monitored in several regions located at various depths from the skull surface. These measurements allowed us to examine the time required for the tissue to reach 0 degree C, in relation to its depth measured from the top of the skull. To define brain regions with proven ischaemia, frozen tissue sections were surveyed for areas of decreased pH. In addition, concentrations of ATP, phosphocreatine, and lactate were determined in gray matter located at various depths from the top of the brain surface. Normal tissue pH and low lactate concentration, without any significant decrease in high-energy phosphate levels, were found in regions at a depth less than approximately 10 mm from the brain surface. Deep structures including the inferiomedial aspect of the temporal lobe, the lateral geniculate body, and the limbic system (hippocampus) consistently showed mild tissue acidosis, indicating that these regions were subjected to some degree of ischaemia before they were reached by the freezing front. In some cases, acidosis was also detectable in the thalamus, basal ganglia, and in the deeper part of some sulci. We conclude that, with baboons, in situ freezing using the box method is valid for metabolic studies of the cerebral cortex and structures located at a depth less than approximately 10 mm from the top of the brain surface.

Animals↗

PubMed1988

Brain tissue concentrations of ATP, phosphocreatine, lactate, and tissue pH in relation to reduced cerebral blood flow following experimental acute middle cerebral artery occlusion.

Local CBF (LCBF) was compared with the corresponding local tissue concentration of ATP, phosphocreatine (PCr), and lactate in anaesthetized baboons subjected to focal ischaemia produced by middle cerebral artery occlusion (MCAO). LCBF hydrogen electrodes were implanted in cortical regions where MCAO had been previously shown to produce severe and penumbral ischaemia and in posterior regions where blood flow is not altered. Metabolites were assayed in small tissue samples collected either by cryoprobe biopsy in the regions where LCBFs were measured (series 1) or by sampling appropriate regions of the rapidly frozen brain (series 2). Subsequent topographical study of brain tissue pH with umbelliferone was performed in this latter series. The results from these two series are compared and discussed in terms of the more appropriate way to perform simultaneous electrode measurements and analysis of tissue samples for studying focal ischaemia in the primate brain. They confirm that the concentrations of ATP and PCr decrease, and that lactate level increases, with decreasing blood flow. These metabolites tended to change more rapidly below a blood flow threshold, rather than showing a steady decrease as the blood flow was reduced, although the variability of the data precluded us from establishing this with confidence. Topographical study of tissue pH often showed sharp boundaries between zones of very low pH and regions with normal pH.

Adenosine Triphosphate↗

PubMed1988

Simple staining for heat-fixed brain sections after topographical pH analysis or autoradiographic studies.

Powerful topographic techniques are now available, among which autoradiographic and fluorescent mapping are the most prevalent. These techniques produce images that usually do not correlate with brain anatomy; subsequent staining is required to allow a precise association between the parameter(s) investigated and brain structures. A simple staining procedure is described, compatible with heat-fixed brain sections, and that was found particularly valuable in association with topographical tissue pH studies using the fluorescent pH indicator umbelliferone.

Autoradiography↗

PubMed1987

Recovery of brain function after ischaemia.

Experimental evidence has recently suggested that early reperfusion following at least focal cerebral ischaemia is accompanied by a return of function which has apparently been suspended during the ischaemic period. The experimental evidence for this is presented. Clinical correlates of this reversible ischaemia sometimes referred to as "penumbral ischaemia" are well known in relation to aneurysm surgery. Several examples are presented in this paper. It is also clear that less easily documented and verifiable recovery from long-term ischaemia may occur in neurosurgery and in interesting case suggestive of this is presented. It involved a middle cerebral occlusion which occurred during the excision of a large meningioma.

Adult↗

PubMed1987

Gliomatosis cerebri: report of a case presenting as a focal cerebral mass.

Gliomatosis cerebri (syn. astrocytomatosis cerebri) is a rare diffuse neoplastic condition affecting all parts of the brain. The clinical and pathological features of an unusually diffuse and histologically uniform case of gliomatosis cerebri are presented. Many tumour cells stained positively for glial fibrillary acid protein, confirming the astrocytic derivation of this neoplasm. Differing views on the nature of gliomatosis cerebri are briefly discussed.

Brain Neoplasms↗

PubMed1987

Intra-operative electrocochleography to monitor cochlear potentials during acoustic neuroma excision.

Intra-operative electrocochleography (ECochG) was used in an attempt to monitor the action potential of the cochlear nerve during acoustic neuroma surgery in 14 patients with useful pre-operative hearing. Five patients had ECochG potentials preserved and yet only three could hear when tested audiometrically later. Of those losing the potentials intra-operatively all were subsequently deaf and the pattern of waveform loss allowed determination of the probable cause of hearing loss. Complete excision of the tumour was achieved in each case regardless of the ultimate effect on the AP as it was not felt justified to risk subsequent recurrence. In common with other studies one of the best prognostic factors for these preservation of hearing was found to be the size of the tumour.

Adult↗

PubMed1987

Clinical evidence supporting a subthalamic origin of the P15 wave of the somatosensory evoked potentials to median nerve stimulation.

Both somatosensory (SSEPs) and brain-stem auditory evoked potentials (BAEPs) were recorded in 3 patients with localized lesions in the thalamus or brain-stem. In one patient with a right thalamic cystic tumour there was a significant interhemispheric difference in the central conduction time (CCT), but the N14-P15 interval was not affected on either side and BAEPs showed normal wave latencies and interpeak latencies (IPLs). The second patient had a colloid cyst of the third ventricle in which central herniation had occurred resulting in 'locked-in' syndrome. The P15 peak was absent on one side and markedly prolonged in latency on the other. BAEPs showed neither wave IV nor V on either side. The third patient had compression of the right posterior rostral pons by a metastatic tumour, resulting in significant prolongation of the CCT on the side of the tumour because of increase in the N14-P15 interval. Both I-V and III-V interpeak latencies were significantly prolonged bilaterally without prolongation in I-III IPL in this case. There was a correlation between the electrophysiological abnormalities of P15 and of BAEP wave V. These results suggest that the origin of the P15, which is usually recorded as a far-field potential, may be in the subthalamus or the upper part of the brain-stem.

Adult↗

PubMed1987

Effects of temporary arterial occlusion on somatosensory evoked responses in aneurysm surgery.

Changes in the central conduction time (CCT) during the application of temporary clips were studied in 40 patients who had undergone operations for intracranial aneurysms in relation to postoperative neurological outcome. Ten of these 40 patients (25%) showed postoperative morbidity, although promptly recoverable in 5. None of the patients whose CCTs did not change following temporary occlusion of major vessels showed any postoperative morbidity, except in one case of anterior cerebral artery aneurysm. In 6 patients, temporary vascular occlusion caused a considerable transient prolongation in CCT of up to 10 msec. Two of these 6 patients were associated with postoperative neurological deficit (which was recoverable in 1). The cortical response became flat in 15 patients. Seven of these 15 patients showed hemispheric deficits postoperatively, although recoverable in 4. There was a correlation between the change in the somatosensory evoked response and postoperative outcome. Disappearance of the N20 potential following occlusion is regarded as a danger signal, but postoperative, irrecoverable neurological deficit seems to be unlikely if its disappearance takes more than 3-4 minutes. Even if the cortical response disappears, the clinical outcome is expected to be good if the N20 potential recovers within 20 minutes after recirculation.

Adult↗

PubMed1987

Temporary vascular occlusion during aneurysm surgery.

Premature rupture of a cerebral aneurysm during operation is a serious hazard. Direct pressure and suction may not always be effective in controlling the hemorrhage, and hasty dissection under such circumstances can cause serious injury to vital structures. In facing this risk, elective temporary arterial occlusion of parent vessels can be an advantage. Temporary clipping also may be helpful in the case of a giant aneurysm when the lesion must be opened and evacuated, or in the case of a thin-walled fundus tightly adherent to perforating vessels. Reduction of tension in the aneurysmal sac can be a valuable aid to safe dissection. The authors reviewed a total of 185 cases of intracranial aneurysm operated upon (L.S.) in the 5-year period between January 1980 and January 1985. Sixty-six patients (35.7%) underwent temporary arterial occlusion during the operations. Clinical outcome was excellent in 65.2% of the patients, good in 13.6%, fair in 12.1%, and poor in 3%. The mortality rate was 6.1%. No significant difference was found by comparing the 66 patients with temporary arterial occlusion with the 119 patients without occlusion. The longest occlusion time for the patients with excellent outcome was 23 minutes for bilateral A1 segments, 40 minutes for middle cerebral artery, 27 minutes 44 seconds for internal carotid artery, and 13 minutes 30 seconds for basilar artery. This study suggests that temporary arterial occlusion does not necessarily increase the overall mortality and morbidity in aneurysm surgery. When justified and used with caution it can be a valuable adjunct for the neurosurgeon.

Adolescent↗

PubMed1987

Hypothalamic glioma.

Seven patients from a series of 400 parasellar lesions presenting with visual failure treated in the Gough-Cooper Department of Neurological Surgery, The National Hospital for Nervous Diseases, Queen Square, were found to have low-grade gliomas of the hypothalamus. All were retrochiasmatic in site. The median age was 18 years. All showed low-grade astrocytoma, grade 2 and, in 6 of the 7 cases, presentation was with a variety of visual problems including homonymous hemianopia, bitemporal hemianopia, and unilateral scotomata. The other case presented with papilledema. Skull x-rays were, by and large, normal. Computed tomography scanning showed low- or mixed-density midline lesions and angiography showed mass effect and occasionally a capsular blush. All were operated on directly through a variety of approaches, and in each case, a radical subtotal removal was carried out. Postoperatively there were no major complications and no major worsening of symptoms in any patient. Radiotherapy was applied in 6 of the 7 cases. Follow-up periods range from 6 months to 6 years and 5 of the 7 patients remain well. The other 2, who are surviving, have advancing neurological disturbance.

Adolescent↗