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Biomedical subjects

L Symon

Publications and source records attributed to L Symon.

At least 73 records · Page 4Linked to original sources
PubMed1991

Cerebrospinal fluid rhinorrhea following acoustic neurinoma surgery. Technical note.

The authors describe a method of preventing cerebrospinal fluid (CSF) rhinorrhea following surgery for acoustic neurinoma. Mastoid air cells exposed during craniectomy are skeletonized and packed with bone dust, then covered with Surgicel soaked with Tisseel fibrin glue. The use of this technique has reduced the number of acoustic neurinoma cases requiring secondary mastoidectomy for CSF leakage from 16% to 5%.

Cerebrospinal Fluid Rhinorrhea↗
PubMed1991

Successful treatment of a pineal endodermal sinus tumor. Case report.

A patient with a pineal endodermal sinus tumor is presented who was successfully treated by a combination of surgery, adjuvant chemotherapy, and craniospinal irradiation. Two years after diagnosis, he is free of any disease. A review of the literature shows that such an outcome is very unusual. A multidisciplinary treatment is recommended for this rare tumor, using chemotherapy as adjuvant treatment.

Adolescent↗
PubMed1991

Intracranial neurenteric cysts. Report of two cases.

Two cases of intracranial neurenteric cysts are reported and the literature is reviewed. Neurenteric cysts are rare congenital lesions that tend to occur in the spinal intradural space. An intracranial location is exceptional.

Adult↗
PubMed1990

Hypoglossal neuroma following excision of a huge recurrent acoustic neuroma and facio-hypoglossal anastomosis. A complex management problem.

A case of neuroma of the intracranial part of the hypoglossal nerve, not associated with neurofibromatosis, is presented. The patient had previously undergone surgery for the removal of a contralateral acoustic neuroma, and subsequent facio-hypoglossal anastomosis. The importance of early diagnosis, pre-operative clinical assessment and post-operative care is stressed.

Adult↗
PubMed1990

The effects of an extradural expanding lesion on regional intracranial pressure, blood flow, somatosensory conduction and brain herniation: an experimental study in baboons.

Intracranial pressure (ICP) differences, change of local blood flow (CBF) using the hydrogen clearance technique, change in the somatosensory evoked potential (SEP) to median nerve stimulation and pupillary size were investigated during progressive elevation of the ICP (using an extradural balloon) in 6 anaesthetized baboons. CBF was measured in the frontal cortex, somatosensory cortex, thalamus (nucleus ventralis posterior lateralis-VPL), medial lemniscus (ML), lateral lemniscus (LL) and caudate nucleus (CN). Conduction along the somatosensory pathway between C2 at the neck and VPL was compared with conduction between VPL and primary somatosensory cortex. The amplitude of the cortical SEP was also studied. ICP gradients between hemispheres developed as the pressure was increased to in excess of 50 mm Hg. CBF was significantly reduced from control in the cortex and VPL on the side ipsilateral to the balloon at 50 mm Hg ICP. A significant decrease in ML flow occurred bilaterally at 70 mm Hg ICP. Conduction time was increased significantly between the right VPL and cortex at a pressure of 50 mm Hg. The amplitude of the cortical response was significantly reduced at 30 mm Hg on the right side and 50 mm Hg on the left. Aniscoria occurred at 50 mm Hg ICP and the pupils became dilated at 70 mm Hg. The SEP was possibly more sensitive than the pupillary reactions as an indication of tentorial herniation in these experiments.

Animals↗
PubMed1990

Bedside monitoring in subarachnoid hemorrhage. Evoked responses, hemispheral blood flow, and flow-velocity measurements.

Bedside measurements of a somatosensory-evoked response, of hemispheral blood flow, and of Doppler flow velocity, therefore, add objective criteria to the other available means of assessment of the condition of an aneurysm patient. Angiography can never be superseded; CT scan with the assessment of the density and distribution of subarachnoid blood has been shown to be of considerable value in relation to spasm, and the fundamental analysis, the view from the foot of the bed by an experienced clinician, can, therefore, be expanded in a variety of collateral ways, all of which will lead over the next few years, to fresh and increased understanding of the vexing question of vasospasm.

Blood Flow Velocity↗
PubMed1990

The effects of experimental brain-stem ischaemia on brain-stem auditory evoked potentials in primates.

We related intracranial auditory brain-stem evoked potentials (BAEPs) to the surface BAEP using a model of focal brain-stem ischaemia. In 17 baboons anaesthetised with alpha-chloralose, BAEPs were recorded bilaterally at the mastoids and in the caudal lateral lemniscus (LL) and inferior colliculus (IC), in response to monaural click stimulation. Electrodes at these sites were each connected to the positive input of a differential amplifier, and one other electrode, placed at the vertex, was connected to all the negative inputs. Measurements of local cerebral blood flow (CBF) by hydrogen clearance were made at the LL and IC sites. The LL wave form contained 5-7 positive peaks, the second (B wave) being dominant and coinciding with the negative wave II of the surface BAEP. Following graded ischaemia, produced by basilar artery occlusion and controlled hypotension, the latency changes of these two peaks were significantly correlated, as were those of the third wave (C wave) of the LL response and the surface wave III. In the IC, the contralateral wave form contained 4 positive waves (A-D) and a later, dominant, slow negative wave; changes in its peak latency and those of the slow negative surface wave were similarly correlated. The thresholds of local CBF for increases in latency of waves B and C in the LL were similar (12-15 ml/100 g/min), but in the IC the thresholds were 20, 30-35 and 20-24 ml/100 g/min for the B, C and slow negative waves, respectively. Our data indicate that a gradient of sensitivity to ischaemia is present along the brain-stem auditory pathways; this could explain the earlier change of the late, rather than early, BAEP components as reported in clinical cases involving brain-stem lesions.

Animals↗
PubMed1990

Jugular foramen neuromas: a review of 14 cases.

We present 14 patients with jugular foramen neuromas treated in the professorial unit at the National Hospital, Queen Square, in the 20-year period from 1969 to 1989. The growth characteristics and associated symptomatology of these tumors are variable, and often they do not give rise to a typical jugular foramen syndrome, making differentiation from other low cerebellopontine angle tumors difficult and occasionally impossible. One tumor presented mainly in the neck, but the remaining 13 were predominantly intracranial and their anatomical relationships as defined radiologically determined the surgical approach used. Nine tumors were resected using a posterior fossa approach, three required a combined posterior fossa and neck dissection, and one a combined supratentorial and infratentorial craniotomy. The aim of operation was total excision of the tumor, which was achieved in 10 patients; the remaining three all suffered recurrence. There was no operative mortality and little long-term disability.

Adolescent↗
PubMed1990

Extracellular striatal dopamine and its metabolites during transient cerebral ischaemia.

Severe cerebral ischaemia has been repeatedly shown to provoke a massive increase in striatal extracellular dopamine (DA). These experiments were undertaken to determine the duration of the DA increase produced by transient ischaemia, and the fate of the released DA during recirculation. Experiments were performed in anaesthetised rats subjected to 20 min of cerebral ischaemia, followed by 80 min of reperfusion, before cardiac arrest. 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 after cardiac arrest. DPV data were substantiated with intracerebral dialysis; 20-min dialysate samples were analysed for DA and homovanillic acid (HVA) using HPLC. In 6 of 11 rats, ischaemia induced a massive DA release in the striatum, resulting in a marked increase in extracellular levels (350-1,200%), which persisted throughout ischaemia. DPV and intracerebral dialysis demonstrated that DA was totally cleared from the extracellular space within minutes of reperfusion, whereas both its acidic metabolites (3,4-dihydroxyphenylacetic acid and HVA) increased slightly. These results indicate that DA released during 20-min ischaemia is rapidly cleared during reperfusion, mainly via reuptake. In the five other rats, only a relatively small and transient increase in the DPV catechol peak was detectable, cleared before the end of ischaemia, probably reflecting less severe ischaemia; small or no changes were detectable in the corresponding dialysate. The latter data suggest that different change(s) in the nigrostriatal dopaminergic system may occur, according to the severity of ischaemia.

Animals↗
PubMed1990

Effect of transient cerebral ischaemia and cardiac arrest on brain extracellular dopamine and serotonin as determined by in vivo dialysis in the rat.

The effects of 20-min transient, global, forebrain ischaemia and cardiac arrest on extracellular concentrations of dopamine (DA), serotonin (5-HT), and their respective metabolites, homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), were measured in vivo by dialysis of rat striatum and hippocampus. During the ischaemic period, striatal DA content increased (250-fold basal concentrations) with parallel but much less marked increases of both striatal and hippocampal 5-HT content (eight- to 10-fold). Baseline values were restored during reperfusion. Subsequent increases of DA and 5-HT levels on cardiac arrest were comparable after both sham operation and ischaemia. Significant decreases of HVA and 5-HIAA levels were observed following ischaemia or cardiac arrest. The differential effects of ischaemia on DA and 5-HT suggest selective alterations in disposition or metabolism of the two transmitters and that dopaminergic neurones may be more vulnerable to ischaemic insults.

Animals↗
PubMed1990

A rapid redistribution of hydrogen ions is associated with depolarization and repolarization subsequent to cerebral ischemia reperfusion.

1. The aim of this study was to examine the rapid changes in extracellular hydrogen ion activity [( H+]o or pHo) which are associated with depolarization and repolarization subsequent to cerebral ischemia reperfusion. Two parallel studies were performed with different rat models of ischemia: repetitive severe ischemia produced in anesthetized animals by occlusion of the vertebral and carotid arteries and temporary interruption of blood flow in isolated brain. [H+]o and direct current potential (DC potential) were recorded simultaneously in all experiments. Examination of these two parameters was supplemented by recording tissue concentration of carbon dioxide (PtCO2) in the four-vessel occlusion model and assaying major metabolites involved in energy production in experiments with isolated brains. 2. Measurements of [H+]o during ischemia consistently revealed a steady increase of [H+]o on which was superimposed an abrupt and transient fall in [H+]o closely related to the occurrence of the fast negative shift of DC potential characterizing brain-cell depolarization. Analysis of the relationship between the magnitude of the transient fall in H+ and the level of [H+]o at which this occurred showed that the amplitude of the transient fall in H+ increased with tissue acidosis. 3. We propose that this phenomenon is indirect evidence that rapid transfer of acid equivalents occurs across the plasmalemma, concomitantly to its depolarization. Both events probably result from a common cause, i.e., nonspecific increase of the cell-membrane permeability to ions subsequent to opening of membrane channels. 4. Early on during recirculation, an acidotic [H+]o shift associated with membrane repolarization was clearly visible whenever the ionic gradients recovered rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1990

Cortical activity, ionic homeostasis, and acidosis during rat brain repetitive ischemia.

Recent data strongly suggest that repetitive ischemic episodes have an adverse cumulative effect on development of edema and tissue damage. We wanted to assess further whether special risks such as exacerbation of extracellular acidification reflecting progressive exhaustion of the capacity to buffer H+ in the extracellular space are associated with repeated short ischemic insults. We monitored spontaneous electrical activity, extracellular direct-current potential, extracellular H+ activity, and tissue PCO2 in the cerebral cortex of rats subjected to four cycles of 3-minute ischemia produced by four-vessel occlusion with 27-minute reperfusion after each insult. Except for electrical activity, which failed to recover fully from the first ischemic insult, all parameters returned to a level close to normal after each reperfusion. Changes during ischemia did not evolve with repetition of the insult. Electrical silence occurred within approximately 20 seconds after the onset of each ischemic episode and always preceded the steep drop of direct-current potential, indicating ischemic depolarization. Each four-vessel occlusion immediately initiated a steep rise of tissue PCO2 and extracellular H+ activity, with extracellular H+ activity reaching a maximum within approximately 145 seconds. Changes in extracellular H+ activity during each recirculation period consistently included an additional and short-lasting increase associated with repolarization, a rapid decrease closely related to that of tissue PCO2, and a slow progressive return to normal. These results suggest that short, repetitive ischemic episodes severe enough to produce cell membrane depolarization and maximum acidosis of the neuronal microenvironment do not have a deleterious cumulative effect on the studied parameters, in particular, on interstitial acidosis.

Acid-Base Equilibrium↗
PubMed1990

Three cases of craniopharyngioma showing optic tract hypersignal on MRI.

Three patients presenting with visual failure had MRIs with hypersignal extending from the region of the optic chiasm along both optic tracts in 2 cases, and along 1 optic tract in the 3rd. In all patients intrinsic tumor of the chiasm was the most likely diagnosis based on MRI appearances, but all 3 had craniopharyngioma.

Adult↗
PubMed1990

Facio-hypoglossal anastomosis for the treatment of facial palsy after acoustic neuroma resection.

Despite current micro-neurosurgical techniques the facial nerve may be irrecoverably damaged in up to 40% of operations for large acoustic neuromas. The results of 121 facio-hypoglossal anastomoses performed since 1960 for post-operative facial palsy are reported. Patients began to recover facial function after an average of 2.5 months and at final follow-up 91% had good function (grade 2 or 3 according to Lye3). The functional result was dependent on the age of the patient, those over 50 years having a poorer, but still acceptable result. The result was not critically dependent on the delay in performing the procedure; in 10 patients with non-functioning but nevertheless intact nerves, the procedure was delayed for 12-15 months to allow for spontaneous recovery, with little detriment to outcome. There was no operative mortality and only minimal morbidity from hypoglossal loss.

Adult↗