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L Symon

Publications and source records attributed to L Symon.

At least 55 records · Page 3Linked to original sources
PubMed1992

A model of acute focal ischemia in the territory of the anterior cerebral artery in baboons.

BACKGROUND AND PURPOSE: We developed a model of acute focal ischemia in the territory of the anterior cerebral artery in baboons to study the ischemic pattern following occlusion and changes in regional cerebral blood flow. METHODS: In nine anesthetized animals, a Scoville clip was placed on the proximal segment of the common anterior cerebral artery via a unilateral transorbital approach. Regional cerebral blood flow was measured by hydrogen clearance in the cortex and corpus callosum. Postexperimentally, arteries were selectively injected. RESULTS: The resulting ischemia involved both hemispheres symmetrically and the corpus callosum. Cortical flows were significantly reduced within a region 15 mm from the midline on each side (p less than 0.01). A gradient of cortical flow reduction was produced between 10 and 25 mm from the midline. This area defines the boundary region between the territories of the anterior and middle cerebral arteries, and is identified as the "penumbra" of the ischemic core, which itself lies within 10 mm of the midline. Blood flows in the corpus callosum decreased from an average of 21.0 to 6.7 ml/100 g/min in the body (p less than 0.01) and from 22.5 to 10.7 ml/100 g/min in the genu (p less than 0.05). CONCLUSIONS: This ischemic model has close physiological and morphological relevance to stroke-related clinical circumstances, in particular the acute conditions of focal cerebral ischemia associated with vascular surgery. It also provides a new framework for experimental investigation of the ischemic penumbra.

Animals↗
PubMed1992

Efflux of glutamate produced by short ischemia of varied severity in rat striatum.

BACKGROUND AND PURPOSE: Evidence has accumulated suggesting that ischemia-induced neuronal damage may be linked to an extracellular overflow of glutamate. The purpose of this study was to provide new information about the time course of the increase in extracellular glutamate concentration associated with moderate and severe ischemia, and its relationship with electrical changes including anoxic depolarization. METHODS: Changes in the extracellular concentration of glutamate were continuously monitored in the rat striatum by microdialysis. Ischemia was induced by four-vessel occlusion for 3 or 5 minutes, and in some cases its severity was increased with a neck tourniquet. The severity of ischemia was assessed by electroencephalogram and direct current potential recording to detect anoxic depolarization. RESULTS: In all experiments, the extracellular glutamate concentration began to increase shortly after the onset of ischemia and steadily rose throughout the ischemic period. Increases up to 35.0 mumol/l (2-3 mumol/l baseline; p less than 0.005) were observed when ischemia provoked the rapid occurrence of a large and sustained anoxic depolarization. Relatively smaller but still significant increases (6.9 mumol/l; p less than 0.005) were observed in penumbral conditions (electroencephalogram loss without anoxic depolarization). Glutamate began to be cleared immediately after reperfusion and 90% of released glutamate was cleared within 5 minutes, even when the preceding ischemia had been severe. CONCLUSIONS: We propose that the extracellular glutamate concentration may not reach critical levels during short episodes of penumbral ischemia, but this might happen with a longer ischemic period.

Animals↗
PubMed1992

Changes in extracellular glutamate concentration produced in the rat striatum by repeated ischemia.

BACKGROUND AND PURPOSE: Evidence suggesting that ischemia-induced neuronal damage may be linked to an extracellular overflow of glutamate has accumulated, and previous studies have shown that repetitive ischemic insults may have a cumulative effect. The purpose of this study was to investigate changes in the extracellular glutamate concentration produced by repeated brief ischemic episodes of varied severity. METHODS: Four consecutive 3- or 5-minute periods of bilateral hemispheric ischemia were produced in rats, each ischemic period followed by 27 minutes of reperfusion. Extracellular glutamate in the striatum was monitored using microdialysis, and the electroencephalogram and extracellular direct current potential were recorded in the same tissue site to assess the severity of ischemia. RESULTS: The results suggest that the kinetics of the increase in the extracellular glutamate concentration produced by a brief ischemic episode are similar, irrespective of whether it is a single insult or part of a repeated sequence. In all cases, the extracellular glutamate concentration increased throughout ischemia and returned to its preischemic level early during reperfusion. The pattern of changes in the ischemia-induced glutamate overflow during repetitive insults varied with the severity of ischemia, in common with the pattern of changes in the direct current potential, supporting the concept that ionic changes associated with anoxic depolarization are a major determinant of ischemia-induced glutamate overflow. CONCLUSIONS: There may be no cumulative effect of brief repeated episodes of ischemia on the extracellular glutamate concentration, even though repeated 5-minute ischemic episodes apparently caused progressive deterioration of ionic homeostasis in some cases.

Animals↗
PubMed1992

Recurrent craniopharyngioma in the posterior fossa.

Craniopharyngioma situated in the posterior fossa is rare. It has been unclear whether such lesions arise primarily in this site or represent direct spread from a suprasellar focus. We report a patient with recurrent craniopharyngioma which had extended into the posterior fossa as far as the cerebellopontine angle through the tentorial hiatus with evidence that it had done so directly. A further separate lesion of similar signal characteristics on MRI scan, lying in the prepontine area, probably represented a seeding from the suprasellar area.

Cranial Fossa, Posterior↗
PubMed1992

Malignant paraganglioma of the glomus jugulare: a case report.

Jugular paragangliomas are noted for their tendency to recur, but frank malignant behaviour is rare. We report a case in which a patient harbouring a recurrent tumour of the glomus jugulare re-presented with metastatic spread to mediastinal lymph nodes. Review of the 16 reported cases provides information which can be a basis for management of the malignant form of this tumour.

Female↗
PubMed1992

Cysticercosis producing various neurological presentations in a patient: case report.

We present an unusual case of neurocysticercosis supported by characteristic lesions on computed tomography and positive serum and CSF titres. The patient came to medical attention on various occasions over a decade with three clearly separate neurological presentations (acute psychosis, cerebral infarction, and hydrocephalus) before diagnosis was made.

Adult↗
PubMed1991

Grading and outcome prediction of cases of aneurysmal subarachnoid haemorrhage by bedside xenon cerebral blood flowmetry.

Ninety-six patients with aneurysmal subarachnoid haemorrhage underwent serial measurement of regional cerebral blood flow throughout the period of their treatment over the period of 5 years (1983 to 1988). A portable bedside xenon cerebral blood flow machine was used in this study and the initial slope index (ISI) values showed a clear relationship between reduction of cerebral blood flow and deteriorating clinical grade. Furthermore, serial measurements showed a statistically significant relationship between drop of cerebral blood flow, at anytime during the course of the disease, and fatal or less than satisfactory outcome.

Adolescent↗
PubMed1991

Changes in rat brain extracellular glutamate concentration during seizures induced by systemic picrotoxin or focal bicuculline injection: an in vivo dialysis study with on-line enzymatic detection.

An on-line enzymatic assay of dialysis fluid has been used to monitor the extracellular glutamate concentration in the rat hippocampus. Perfusion with artificial cerebrospinal fluid containing a glutamate uptake inhibitor (either dihydrokainate or 4,4'-diisothiocyanatostilbene-2,2' disulfonic acid) produced a marked stable increase in glutamate concentration; 10 min perfusion with 100 mM K+ produced a transient increase. Sustained epileptiform EEG discharges were induced in the hippocampus by focal injection of bicuculline into the piriform cortex or by systemic injection of picrotoxin. Extracellular glutamate did not change significantly during seizure activity, either in the absence or in the presence of glutamate uptake inhibitors. It is concluded that seizure activity is not necessarily accompanied by an overall increase in extracellular glutamate concentration.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Noninvasive intraoperative monitoring of motor evoked potentials under propofol anesthesia: effects of spinal surgery on the amplitude and latency of motor evoked potentials.

We present the results of intraoperative monitoring of motor evoked potentials from 34 patients undergoing spinal surgery under total anesthesia with intravenously administered propofol. Intraoperative recording was performed with transcranial electrical stimulation. Two groups of patients were studied: 1) a control population of 26 patients undergoing lumbar discectomy for prolapsed intervertebral disc, all of whom had normal preoperative motor conduction; and 2) a population of 8 patients undergoing neurosurgical procedures for spinal tumor (5 patients) and spinal arteriovenous malformation (3 patients), all of whom had abnormal preoperative neurological signs and abnormal preoperative motor conduction. In the first group, electromyographic responses were recorded intraoperatively either from the 2nd dorsal interosseous muscle of the hand (5 patients) or from the 1st dorsal interosseous muscle of the foot (21 patients). In the second group, responses were recorded intraoperatively either from the 1st dorsal interosseous muscle of the foot (7 patients) or from the anterior tibial muscle (1 patient). Intraoperative monitoring of motor function was successful in 88.5% of the patients in the control group. Propofol anesthesia caused a reduction in response amplitude to 7% of baseline values obtained from conscious relaxed subjects. Intraoperative monitoring was successful in 87% of the patients in the pathological group. We observed significant changes in both amplitude (greater than 50%) and/or onset latency (greater than 3 ms) from the intraoperative baseline that indicated either improvement (3 patients) or deterioration (2 patients) in motor conduction within minutes of surgical maneuvers anticipated to alter spinal cord function. Only permanent complete loss of intraoperative motor conduction (1 patient) correlated with a significant change in the postoperative neurological state.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Effects of nitrous oxide on motor evoked potentials recorded from skeletal muscle in patients under total anesthesia with intravenously administered propofol.

The effect of nitrous oxide (N2O) on motor evoked potentials (MEPs) recorded from human subjects under total intravenous anesthesia with propofol (2,6-diisopropylphenol) was studied. MEPs were recorded from the 1st dorsal interosseous muscle of the foot in nine subjects; in two of these, simultaneous recordings were made from the 2nd dorsal interosseous muscle of the hand and from the deltoid muscle. Single transcranial electrical stimuli were used in recording the MEPs. The effects of N2O were studied at concentrations from 20 to 70%. Increasing concentrations of N2O caused a progressive increase in onset latency and a fall in the peak-to-peak amplitude of the MEPs recorded from the foot. Latency values showed a significant increase above the baseline at concentrations of N2O greater than 20% (P values, 0.05-0.005). The response amplitude showed a significant decrease from the baseline at concentrations of N2O greater than 50% (P values, 0.05-0.005). The 2nd dorsal interosseous muscle of the hand demonstrated a pattern of sensitivity to N2O similar to that of the 1st dorsal interosseous muscle of the foot. The onset latency and initial peak-to-peak amplitude of the deltoid muscle were insensitive to N2O at the concentrations used. We conclude that N2O can be used as an anesthetic adjunct without a significant deleterious effect on MEPs during intraoperative monitoring in patients under propofol anesthesia, providing concentrations are maintained below 50%.

Adult↗
PubMed1991

The impact of continuous electrophysiological monitoring on preservation of the facial nerve during acoustic tumour surgery.

Continuous electromyographic (EMG) activity and responses to electrical stimulation of the facial nerve were monitored intraoperatively in 35 patients undergoing primary removal of acoustic neuroma. The rate of anatomical and immediate functional preservation of the facial nerve of these patients was compared with a matched population where a facial nerve stimulator and monitoring of facial muscle contraction by the anaesthetist only was employed. Overall, 94% (n = 33) of facial nerves were preserved anatomically in patients with continuous EMG monitoring, compared with 64% (n = 89) of patients (n = 139) without continuous monitoring. Amongst the 33 cases with anatomical facial nerve preservation, 64% (n = 21) had immediate functional preservation. Immediate functional preservation was only achieved in 39% (n = 35) of anatomically preserved facial nerves (n = 89) where conventional monitoring was used.

Electromyography↗
PubMed1991

Cavernous angioma of the cerebello-pontine angle: a case report.

A case of cavernous angioma involving the facial nerve is described. The patient presented with decreased hearing on one side and after investigation a small mass was discovered enlarging the internal auditory meatus. The final diagnosis was made at operation. The pathology of this type of malformation is discussed.

Adult↗
PubMed1991

Surgical treatment of pontomedullary cavernomas.

Direct treatment of brainstem cavernous haemangiomas (cavernomas) naturally represents a considerable surgical challenge due to the close proximity of vital structures. The results of such treatment have only rarely been described. We report our experience in the management of seven patients with cavernomas of the brainstem treated by microsurgical resection. All patients presented with neurological symptoms directly attributable to one or more episodes of brainstem haemorrhage. CT scan examination in all cases revealed either obvious haematoma or a focal region of high density within the pons or medulla; calcification in and around the lesion was detected in two patients. MRI scanning was performed in four of our cases and was strongly suggestive of the diagnosis of cavernoma with evidence of both recent and older haemorrhage as evidenced by haemosiderin deposits. Cerebral angiography failed to disclose abnormal vessels to the cavernoma in any instance, although interestingly a co-existent but separate cerebellar venous malformation was observed in two of our cases. Surgery was performed between 19 days and 3 months following the most recent haemorrhage. Microsurgical removal of both haematoma and underlying cavernoma was accomplished either via a median suboccipital or retromastoid craniectomy, with an appropriate incision being made into that part of the brainstem most directly overlaying the lesion. Significant improvement in neurological function has followed in all seven cases. Although the natural history of symptomatic cavernous haemangiomas is incompletely understood, the favourable results obtained in our patients suggest that total surgical removal is both practicable and relatively safe even in the case of those lesions situated within the brainstem.

Adult↗
PubMed1991

Magnetic resonance demonstration of the effect of carotid artery ligation for a giant internal carotid artery aneurysm: case report.

Ligation of the carotid artery remains an accepted treatment for unclippable giant carotid artery aneurysms. Post-operative evaluation is commonly made subsequently by CT scan and angiography, the latter involving an invasive procedure. This paper describes the magnetic resonance (MR) appearance of a traumatic giant terminal carotid artery aneurysm treated by common carotid ligation. MR appears to be the imaging technique of choice for follow-up of giant aneurysms of the terminal carotid artery treated by carotid ligation, the accuracy of delineation of the aneurysm and its content surpassing that of the CT scan.

Adult↗
PubMed1991

Radical excision of craniopharyngioma by the temporal route: a review of 50 patients.

Attempts at radical excision of craniopharyngioma have been made increasingly possible by progress in neuroradiological imaging and the use of microscopic technique. Between 1977 and 1990, 50 patients of The National Hospital for Neurology and Neurosurgery, London, have undergone radical surgical excision of craniopharyngioma by the temporal route, with a small anterior temporal resection. Surgical mortality was 4%. Thirty-eight (76%) patients remain well at average follow-up of 30 months; 15% had major complications (hypothalamic damage, subdural haematoma, scalp collections requiring shunt drainage). There were three recurrences in those patients where the initial operations were considered as complete microscopic excision. It is concluded that maximal control of tumour recurrence by removal of all tumour accessible and visible to the surgical microscope is best achieved by a radical excision at the first operation.

Adolescent↗