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Biomedical subjects

L Symon

Publications and source records attributed to L Symon.

At least 127 records · Page 7Linked to original sources
PubMed1987

pH, K+, and PO2 of the extracellular space during ischaemia of primate cerebral cortex.

pH and K+ from the extracellular space, PO2, and CBF have been measured in the same region during progressive ischaemia of primate cerebral cortex. As blood flow was reduced, the other changes had the following sequence. PO2 fell rapidly to 30% of control levels at regional CBF (rCBF) of 30 ml 100 g-1 min-1. As CBF was further reduced, PO2 continued to fall. pH remained stable until around 20 ml 100 g-1 min-1, below which pH fell rapidly, with an exponential increase in H+ concentration. K+ showed the well-known relationship to CBF, remaining normal until around 10 ml 100 g-1 min-1, below which K+ rose rapidly. pHe and log K+ were lin-early related and confirmed that pH fell by 0.3 U before K+ rose significantly, and fell by 0.6 U before the massive rise in K+. The mechanisms involved in this sequence of events and the role of pH changes in the development of the so-called "ischaemic penumbra" are discussed.

Animals↗
PubMed1987

The clinical significance of the P15 wave of the somatosensory evoked potential in tentorial herniation.

Somatosensory evoked potentials (SEPs) to median nerve stimulation and auditory brainstem evoked potentials (BAEPs) were recorded in 16 comatose patients who had suffered transtentorial herniation (TH) due to intracranial haematoma, hydrocephalus or tumour. An attempt was made to correlate the changes in the N14-P15 component of the central conduction time (CCT) and the I-V interpeak latencies (IPLs) of the BAEP with the clinical severity of TH. The N14-P15 component was not affected in seven patients at the diencephalic or early third-nerve stage, and six of these seven showed normal I-V IPLs. All six patients at the late third-nerve/midbrain stage or worse, however, showed abnormalities in the N14-P15 components. Interestingly, five patients showed dissociation of SEP and BAEP abnormalities suggesting a differential sensitivity of the medial and lateral lemnisci in the brainstem to ischaemia and/or compression. All five patients in whom the P15 potential was absent on either side had a poor outcome and there was a correlation between the electrical failure in the N14-P15 component and the degree of brainstem damage caused by TH as assessed clinically. Reversible loss of the P15 potential by brainstem retraction has been shown in intraoperative SEP monitoring during aneurysm surgery. Prolonged compression of the upper brainstem seems to cause irreversible loss of the P15 which should be regarded as being due to irrecoverable brainstem dysfunction.

Adolescent↗
PubMed1987

Cerebral blood velocity in subarachnoid haemorrhage: a transcranial Doppler study.

A study examining the utility of transcranial Doppler ultrasound for the determination of cerebral vasospasm following subarachnoid haemorrhage is reported. A control group of 21 patients and a second group of 20 patients suffering from subarachnoid haemorrhage or aneurysm and a group of 26 with other intracranial pathologies were studied. The Doppler flow velocity (DFV) was significantly higher when vasospasm was present. If it was higher than 100 cm/s, the patients were found to have vasospasm in 80% of cases. If Doppler flow velocity was below 100, less than 10% had spasm. Doppler flow velocity was not found to increase following craniotomy in patients not suffering from subarachnoid haemorrhage. In subarachnoid haemorrhage patients there was a trend to increased Doppler flow velocity especially in patients who developed neurological deficit. Doppler flow velocity and Initial Slope Index by xenon clearance (ISI) were not found to correlate with clinical grade. The ISI/DFV quotient (which can be shown mathematically to be related to vessel diameter) was found to correlate well with clinical grade. In this largely post-operative group, absolute levels, or rate of change of Doppler flow velocity could not be shown to be related to the onset or existence of neurological deficit.

Adult↗
PubMed1987

Epidermoid cysts and cholesterol granulomas centered on the posterior fossa: twenty years of diagnosis and management.

The clinical features, diagnosis, and management of 23 posterior fossa epidermoid cysts and 9 petrous apex lesions presenting to one unit over a period of 20 years are summarized. Of the epidermoid cysts, 13 were entirely infratentorial, but the other 10 had an additional supratentorial component. Presenting symptoms and signs were usually long-standing and at onset had often been vague and nonspecific. With time, however, a variety of neurological deficits that depended on the site of the lesion developed. These were generally combinations of cerebellopontine (CP) angle and jugular foramen syndromes, deafness, facial palsy, and motor weakness. Diagnostic procedures have changed greatly over the review period. Computed tomography and magnetic resonance imaging have replaced air encephalography and contrast ventriculography. The better preoperative localization of these lesions allows rational planning of the surgical approach required for optimal tumor exposure, which is essential for any attempt at total excision, considering the large size of the majority of these tumors when diagnosed. We favor operation through a posterior fossa craniectomy for those tumors restricted to the CP angle or 4th ventricle, but routinely use a combined supra- and infratentorial approach if the lesion has a more rostral component. The infiltrating nature of epidermoid cysts within the cranium compromises the extent of excision if neurological deficit is not to be increased, but we attempt as complete an excision of tumor and capsule as possible in the hope that many years will pass before symptoms recur. Cholesterol granulomas seem to respond well to simple cavity drainage and have shown no tendency to recur.

Adolescent↗
PubMed1987

Preservation of cochlear potentials in a deaf patient fifteen months after excision of an acoustic neuroma.

Intraoperative electrocochleographic monitoring has been used in an attempt to protect cochlear nerve function during acoustic neuroma excision. One patient is presented with an apparently intact cochlear nerve and waves N1 and N2 preserved at the end of surgery, but no hearing on subsequent testing. Fifteen months after operation, cochlear microphonics and the summating potential were still present, but N1 and N2 had disappeared. There had been no improvement in her hearing and there were no consistent brainstem auditory evoked potentials on the affected side. A possible explanation for these findings is given.

Adult↗
PubMed1987

Catecholamine-secreting paragangliomas of the base of the skull. Report of two cases.

Two cases of catecholamine-secreting paragangliomas of the base of the skull are described. The patients presented with uncontrollable hypertension and, after investigation, tumors were discovered in the regions of the glomus jugulare and pterygopalatine ganglion, respectively. After cardiovascular stabilization and tumor embolization, the tumors were surgically removed, with subsequent resolution of hypertension. The incidence of these tumors is discussed.

Adult↗
PubMed1986

Intraventricular meningioma. A review of 10 cases of the National Hospital, Queen Square (1974-1985) with reference to the literature.

Ten patients with histologically verified intraventricular meningiomas were treated between 1974 and 1985. There were eight female and two male patients, ranging in age from 25 to 72 years with a mean age of 45.5 years. Headache and disturbed mentation were the most common presenting symptoms whereas corticospinal disturbance, altered mentation and homonymous hemianopia were the most common signs on formal neurological examination. Papilloedema was demonstrable in 50% of cases and evidence of dysphasia was apparent in 60% of patients with lesions affecting their dominant hemisphere. A single instance of drop attack occurred in a patient harbouring a third ventricular meningioma. Computed tomography, with and without contrast enhancement, and angiography were employed in all cases and proved highly sensitive and specific for tumour localisation and tissue diagnosis. In addition, angiography proved invaluable in demonstrating both vascular supply and the effects imposed upon the surrounding cerebral vasculature by tumour mass and hydrocephalus. Nine tumours occurred in the lateral ventricular trigone of which 5 were left-sided. A tenth tumour was located in the third ventricle. Twelve resections were performed in 10 patients. One patient was found to have a highly malignant cystic meningioma which recurred within 10 weeks of the original surgery and proved fatal shortly thereafter. A second patient whose initial resection was subtotal had a recurrence 3 years postoperatively which was totally resected. Lesions were approached most commonly through the posterior middle or posterior inferior temporal gyri. On 3 occasions a right posterior middle frontal gyrus approach was used and in one case a posterior parieto-occipital cortical incision was employed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Effects of an expanding supratentorial mass on the auditory brain-stem responses in baboons.

This study was carried out to investigate the effects of an expanding supratentorial mass on auditory brain-stem responses (ABRs). A balloon was inserted into the supratentorial epidural space of seven baboons (in two cases, in the right occipital area; in five cases, in the right temporal area). The balloons were inflated at a rate of 0.2 ml/minute to increase intracranial pressure (ICP). ICP (right frontal epidural pressure) and blood pressure (BP) were continuously recorded. Recordings of ABRs (vertex to mastoid on both sides) were made serially. Pupillary changes were also recorded. At 30 mmHg ICP, the amplitude of wave V on the right side was observed to be significantly attenuated (p less than 0.02). At 50 mm Hg ICP, the latency of wave V on the right side was significantly prolonged compared with that at 30 mm Hg ICP (p less than 0.02). At 70 mmHg ICP, significantly decreased amplitude of wave V on the left side was also observed (p less than 0.02, from the control), associated with significant increased latency of wave IV on the right side (p less than 0.01, from the control; p less than 0.05, from 50 mm Hg ICP). Finally, waves IV and V on both sides substantially disappeared at 100 mm Hg ICP. Anisocoria appeared in four animals at 30-50 mm Hg (mean +/- SD; 45 +/- 8.7) ICP. The amplitude of wave V was significantly decreased in these circumstances (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Posterior fossa ependymomas in adults.

Sixteen patients with posterior fossa ependymomas are presented. This tumour is relatively uncommon in adults and is usually associated with a relatively "benign" course when compared with other posterior fossa glial tumours. The natural history and treatment of these tumours is discussed.

Brain Neoplasms↗
PubMed1986

The use of brainstem auditory evoked potentials during posterior fossa surgery as a monitor of brainstem function.

Nine patients with unilateral ponto-cerebellar tumour, one with epidermoid, eight with acoustic neuroma had intraoperative monitoring of the brainstem auditory evoked potentials (BAEP) using bilateral scalp recording (Cz-A1 and Cz-A2) and binaural stimulation in order to monitor brainstem function during the surgery. Results were correlated with preoperative and postoperative BAEP findings. There was some intraoperative BAEP change in all the patients. Halothane anaesthesia caused bilateral wave V. prolongation in six patients. Lumbar drainage produced ipsilateral or bilateral wave V. prolongation in three of four patients in whom lumbar drainage was established. Opening the dura produced ipsilateral or bilateral wave V. depression or bilateral prolongation in four patients. Tumour dissection caused BAEP changes in all the patients: bilateral prolongation or depression in five patients, and ipsilateral prolongation and/or depression in six patients, three of them together with bilateral changes. The only patient who had no changes in wave I-IV. but in whom a big wave VI. appeared at the tumour side during removal, had epidermoid tumour. At the end of surgery there was some improvement in all patients, but in two the improvement was not striking: in one BAEP remained flat ipsilaterally, and in other, latency did not improve. All the patients had a good clinical recovery a few days later, but the control BAEP performed from the 3rd-7th postoperative day was not yet completely recovered in four patients. Intraoperative BAEP monitoring can be a useful technique to monitor brainstem function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

The effects of a supratentorial mass lesion on brain-stem auditory evoked potentials and short latency somatosensory evoked potentials.

Nineteen patients with unilateral supratentorial mass lesion and without any evident clinical signs of transtentorial herniation were studied with Computed Tomography (CT), brain-stem evoked potentials (BAEPs) and central conduction time (CCT) of short latency somatosensory evoked potentials (SEPs). Sixteen had tumours, two had intracranial haematoma and one had chronic subdural haematoma. CT detected the initial signs of transtentorial herniation in every case. Preoperative I-V interpeak latency (IPL) was significantly (M + 2SD) prolonged in 26% of cases on the lesion side and in 21% of cases on the opposite side. The mean I-V IPL was significantly prolonged both on the lesion side and the opposite side (P less than 0.01, P less than 0.02, respectively). Suppression of Wave V (M-2SD) was seen only in two cases, however, the mean amplitude of Wave V was significantly decreased both on the lesion side and on the opposite side (P less than 0.001, P less than 0.01, respectively). CCT of SEPs was significantly (M + 2SD) prolonged in 33% of cases on the lesion side and in only 13% on the opposite side. The mean CCT was, however, significantly prolonged both on the lesion and on the opposite side (P less than 0.001, P less than 0.02, respectively). Postoperative I-V IPL was significantly prolonged in only 11% of cases while the mean I-V IPL was still significantly prolonged (P less than 0.01) and the mean amplitude of Wave V was still suppressed (P less than 0.001) on the lesion side.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Comparison of fast flow and initial slope index values for cerebral blood flow following subarachnoid haemorrhage.

Forty five patients with subarachnoid haemorrhage proved by lumbar puncture underwent serial measurements of cerebral blood flow and central conduction time. When the initial slope index (ISI) value for cerebral blood flow is considered there is a clear relationship between reduction of cerebral blood flow and deteriorating clinical grade. This relationship is not so clearly demonstrated using the fast flow (f1) value for cerebral blood flow. When cerebral blood flow is compared to central conduction time those patients with a central conduction time longer than 6 X 4 ms have a significantly lower CBFisi but not a significant lower CBFf1. Furthermore, using the ISI value, there is a linear relationship between the fall in cerebral blood flow and the lengthening of CCT below a threshold blood flow of about 35 ml/100 g/min. This relationship is not demonstrated with the CBFf1 value. It therefore appears that the ISI value for cerebral blood flow shows a greater correlation between clinical and electrophysiological events than the f1 value.

Adolescent↗
PubMed1986

Meningiomas of the clivus and apical petrous bone. Report of 35 cases.

Between March, 1966, and June, 1985, 23 women and 12 men underwent partial or total resection of apical petrous or clivus meningiomas at The National Hospital for Nervous Diseases. Presenting symptoms were typically of long duration (mean 29 months) and consisted primarily of gait disturbance, headache, hearing loss, and facial pain. Cranial nerve deficits, especially affecting the fifth, seventh, and eighth nerves. were observed in nearly every patient. Tumor size, but not location, was generally associated with degree of preoperative disability. Plain skull films were usually unremarkable, but computerized tomography (CT) proved highly accurate in determining tumor location and size. A characteristic pattern of vascular displacement was seen on vertebral angiograms, although blood supply to the tumors was derived primarily from branches of the internal and external carotid arteries. Subtotal or total resection was undertaken in all cases; nine patients required adjunctive cerebrospinal fluid shunting procedures. Although surgical techniques evolved during the course of the 20-year study, a combined supra- and infratentorial approach proved a relatively safe and effective means of surgical treatment. New or worsened postoperative deficits, especially cranial nerve palsies, and complications in the immediate postoperative period frequently resulted in temporary deterioration of the clinical status during this period; the total operative mortality rate was 9%. Follow-up periods ranged up to 9 years; 70% of patients resumed an independent existence, and none is known to have required subsequent tumor surgery. The size of the lesion was the only significant factor in determining outcome. These data suggest that meningiomas of the clivus and apical petrous bone can be accurately diagnosed by CT and three-vessel angiography, and effectively treated by microsurgical resection.

Adult↗
PubMed1986

Chlormethiazole in the management of post-craniotomy seizures.

Epilepsy is an important problem in the period immediately following intracranial surgery. Rapid control of seizures is important to prevent damage to cerebral neuronal function. A method of managing epilepsy using intravenous chlormethiazole is reported. This regimen has proved to be safe and rapidly effective in the control of post-operative seizures.

Brain Diseases↗