Biomedical subjects

F B Meyer

Publications and source records attributed to F B Meyer.

At least 91 records · Page 5Linked to original sources

PubMed1994

Blinded prospective evaluation of sensitivity of MR angiography to known intracranial aneurysms: importance of aneurysm size.

PURPOSE: To determine the sensitivity of time-of-flight and phase-contrast MR angiography for the detection of intracranial aneurysms. METHODS: Sixteen patients with 27 intracranial aneurysms previously identified with conventional angiography and 19 control patients were examined with three-dimensional time-of-flight, three-dimensional phase-contrast MR angiography, and standard MR imaging. Subvolumes of the carotid and posterior circulations, source images, and standard MR images were blindly interpreted by three experienced neuroradiologists. RESULTS: Detection of an aneurysm by a given sequence was defined as at least two of the three blinded readers identifying the aneurysm. The sensitivities of the sequences based on all 27 aneurysms were: transaxial T1, 25.9%; T2, 48.1%; PC, 44.4%; and TF, 55.6%. Two of 3 aneurysms detected with T2 but not MR angiography had adjacent blood products. Five millimeters appeared to be a critical size; the sensitivities for aneurysms greater than or equal to 5 mm were: T1, 37.5%; T2, 62.5%; PC, 75%; and TF, 87.5%. CONCLUSIONS: Three-dimensional time-of-flight MR with 512 x 256 matrix is more sensitive than three-dimensional phase-contrast or standard MR imaging for detection of aneurysms. Retrospectively, aneurysms 3 mm or larger can be identified with MR angiography; however, prospectively, 5 mm is the critical size for detection.

Adult↗

PubMed1994

Carotid stenosis and carotid endarterectomy.

This review focuses on the natural history of symptomatic and asymptomatic carotid stenosis and on the risk/benefit ratio of carotid endarterectomy. Five randomized trials for symptomatic stenosis and four trials for asymptomatic carotid occlusive disease are reviewed. Carotid endarterectomy has been proved effective in reducing stroke risk in symptomatic 70-99% stenosis. Conclusive results are still pending for moderate symptomatic stenosis and the asymptomatic lesion. Surgical controversies and techniques are discussed. Algorithms for management of symptomatic and asymptomatic stenosis are offered.

Aging↗

PubMed1994

Reconstruction of previously ligated external carotid arteries for cranial base arteriovenous malformation embolization: technical note.

Ligation of the external carotid artery has been used in the past as a treatment for cranial base and facial arteriovenous malformations. By current selective embolization techniques, this prior ligation of the external carotid artery may hinder optimal treatment. Reported here are the indications and surgical techniques used for reconstructing previously ligated external carotid arteries in preparation for endovascular treatment. Direct reconstruction or an interposition graft was useful, depending on the patient's anatomy. There were no complications in this series, despite the presumed increase in blood flow to the arteriovenous malformation after reconstruction. After reconstruction, early embolization is feasible and may be necessary to prevent the engorgement of the arteriovenous malformation.

Adult↗

PubMed1993

Spontaneous midbrain hemorrhage: report of seven new cases.

Spontaneous midbrain hemorrhage is a unique brain-stem vascular lesion. Sixty-six cases have been reported in the literature, to which we add seven. Of the total of 73 patients reviewed, most presented acutely (66%), but subacute (22%) and chronic onsets (12%) also occurred. Neuro-ophthalmologic abnormalities were found in 88% of patients. Some alteration of consciousness and headache occurred in most patients. Hemiparesis, hemisensory loss, and ataxia were less frequent manifestations. Vascular malformations were suspected or proved in 37% of patients, hypertension was present in 21%, and a bleeding diathesis was noted in 5%. No underlying cause was apparent in 37%. Most patients improved with supportive care only. At follow-up, 23% of patients had no neurologic deficits. In 51% of patients, minor neurologic deficits persisted, related chiefly to cranial nerves III and IV. Moderate deficits persisted in 16% of patients, and 5% of patients died.

Adolescent↗

PubMed1993

Effect of arterial blood pressure and serum glucose on brain intracellular pH, cerebral and cortical blood flow during status epilepticus in the white New Zealand rabbit.

Generalized seizures can induce both hypertension and hyperglycemia which may aggravate preexisting cerebral or medical conditions in patients. In vivo fluorescent imaging of regional cortical blood flow and brain intracellular pH (pHi) was performed in fasted New Zealand rabbits (n = 35) in which either mean arterial blood pressure (MABP) or serum glucose was the covaried factor during pentylenetetrazole induced status epilepticus under 1.5% inspired halothane. Baseline brain pHi and regional cortical blood flow were 7.02 +/- 0.02 and 51.1 +/- 1.7 ml/100 g/min, respectively. Following seizure induction, MABP increased to 105 mm Hg and brain pHi fell to 6.79 +/- 0.03 within 15 min and remained at this level for 1 h (P < 0.001). With normalization of MABP during ongoing seizures, there was no worsening in brain pHi despite a significant decrease in regional cortical blood flow. Hyperglycemia decreased pHi to 6.71 +/- 0.02 compared to 6.84 +/- 0.04 in normoglycemic animals (P < 0.001). Using pHi as a cerebral metabolic index, these data suggest that normalization of MABP does not increase metabolic injury while hyperglycemia does significantly worsen brain acidosis. Therefore, administration of glucose to patients with status epilepticus should be avoided unless there is documented hypoglycemia.

Animals↗

PubMed1993

Quantitative MRI hippocampal volumes: association with onset and duration of epilepsy, and febrile convulsions in temporal lobectomy patients.

The relationships between preoperatively acquired MRI-based hippocampal volumes (HV), seizure disorder onset and duration, and early childhood febrile convulsions were investigated retrospectively with data from 72 left and 56 right temporal lobectomy patients. Patients with lesional pathology and heterotopic abnormalities were excluded. Age at development of spontaneous seizures unprovoked by an acute illness defined age of seizure disorder onset. Age of onset was subtracted from age at neurosurgery to determine duration. MRI variables included in this study were the right and left HV divided by total intracranial volume (RAHV, LAHV), and the right-left hippocampal difference (DHF). Partial correlations were used to better isolate relationships with onset of recurrent seizures corrected for age at surgery, and age at neurosurgery corrected for age of recurrent seizure onset. Partial correlations between age at neurosurgery and volume were not significant in either group. LAHV (r = 0.42, P < 0.0003) and DHF (r = -0.49, P < 0.0001) were correlated with age of onset in the left lobectomy group. Correlations in the right lobectomy group were not significant. The presence of a febrile convulsion was associated with smaller LAHV (F(1,70) = 10.54, P < 0.002) and larger DHF (F(1,70) = 11.36, P < 0.002) in left temporal lobectomy patients. The presence of a febrile convulsion in the right temporal group was associated with a slightly smaller DHF (F(1,56) = 5.90, P < 0.02), and slightly smaller RAHV (F(1,56) = 4.49, P < 0.04). These data suggest that hippocampal atrophy remains stable over the duration of temporal lobe onset seizure disorders, and is associated with early onset of recurrent seizures in left temporal patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Carotid endarterectomy in patients with contralateral carotid occlusion.

In this study, we assessed the results of carotid endarterectomy in 357 patients with a carotid stenosis and contralateral carotid occlusion. The overall major neurologic morbidity was 0.6%, and the minor morbidity was 1.1%. The causes of four perioperative deaths (1.1%) were myocardial infarction in two patients, ruptured abdominal aortic aneurysm in one, and respiratory complications in one. Therefore, an excellent result was achieved in 97.2% of patients. With occlusion of the carotid artery for the endarterectomy, 165 patients (46%) had appreciable attenuation in intraoperative electroencephalographic findings and a decrease in cerebral blood flow to approximately 10 ml/100 g of brain tissue per min that necessitated placement of a shunt. This high percentage of profound electroencephalographic and blood flow changes during carotid occlusion suggests that the potential for collateral blood flow in this group of patients is minimal. These results demonstrate that a carotid endarterectomy can be performed at low risk in patients with a contralateral carotid occlusion. We advocate annual noninvasive carotid testing for patients with asymptomatic carotid stenosis and contralateral carotid occlusion. If progression of the stenosis is evident, a prophylactic endarterectomy should be considered because these patients may have a higher risk for cerebral infarction than do patients with a unilateral asymptomatic stenosis.

Aged↗

PubMed1993

Carotid artery: prospective blinded comparison of two-dimensional time-of-flight MR angiography with conventional angiography and duplex US.

A prospective blinded comparison of two-dimensional (2D) time-of-flight (TF) magnetic resonance (MR) angiography and color duplex flow ultrasound (US) with conventional angiography as a standard of reference was performed in 50 patients with hemispheric ischemic symptoms. The guidelines of the North American Symptomatic Carotid Endarterectomy Trial for measuring stenosis of the internal carotid artery were utilized for maximum-intensity-projection (MIP) images and conventional angiograms. While the 2D TF MIP technique overrepresented the degree of stenosis in the internal carotid arteries, it matched the performance of color duplex flow US as measured by means of receiver operating characteristic curves. A signal void on the MIP images corresponded to a 70% or greater internal carotid artery stenosis in 17 of 20 arteries. At its current state of development, the accuracy of 2D TF MR angiography equals that of US in characterizing the degree of carotid stenosis but cannot be considered a replacement for conventional angiography.

Adult↗

PubMed1993

Effect of superhypercapnia on cortical pHi and cortical blood flow.

In vivo panoramic imaging of regional cortical blood flow and intracellular brain pH with umbelliferone fluorescence was performed in fasted New Zealand White rabbits (n = 30) subjected to constant or stepwise increases in arterial PCO2 (PaCO2) up to 160 mmHg under 1.0% halothane anesthesia. At a PaCO2 of 40 mmHg, baseline brain pHi measured 7.03 +/- 0.04, while regional cortical blood flow was 47.0 +/- 4.3 ml.100 g-1.min-1. With an immediate but constant exposure to a PaCO2 of 60, 80, or 120 mmHg, at 15 min pHi fell to 6.94 +/- 0.03, 6.89 +/- 0.03, and 6.90 +/- 0.03 and recovered over 20, 80, and 120 min, respectively. At 160 mmHg PaCO2, pHi fell to 6.68 +/- 0.04 and remained acidotic. With stepwise increases in PaCO2 up to 80 mmHg, brain pHi decreased from 7.01 +/- 0.02 to 6.99 +/- 0.02, not significantly different despite a severe systemic acidosis of 7.022 +/- 0.034. At a PaCO2 of 120 and 160 mmHg, pHi dropped to 6.97 +/- 0.02 and 6.93 +/- 0.02, respectively. The difference in brain pHi between an immediate and stepwise exposure to a PaCO2 of 160 mmHg was significant (P < 0.005). These results demonstrate that brain pHi is tightly regulated across the cortical surface and resistant to profound changes in extracellular pH. The difference in pHi between the constant and incremental increases in PaCO2 suggests that there is upregulation of pH homeostatic mechanisms.

Animals↗

PubMed1993

Acidic foci within the ischemic penumbra of the New Zealand white rabbit.

BACKGROUND AND PURPOSE: In vivo panoramic imaging of reduced nicotinamide adenine dinucleotide (NADH), intracellular brain pH (pHi), and cortical blood flow was used to characterize the ischemic penumbra during focal ischemia. During global ischemia, hypoxia, and status epilepticus, the development of cortical acidic foci has been observed. The hypothesis tested was that during focal ischemia, acidic foci develop, which may lead to recruitment of the ischemic penumbra into infarction. METHODS: Five fasted New Zealand White rabbits underwent middle cerebral artery (MCA) occlusion under 1.5% halothane anesthesia through a retro-orbital approach, and five animals served as controls. Brain pHi and cerebral blood flow were measured with in vivo umbelliferone fluorescence. RESULTS: Baseline brain pHi was 6.98 +/- 0.05, whereas cortical blood flow and NADH fluorescence measured 52.2 +/- 8.7 mL/100 g per minute and 35.5 +/- 3.7 gray-scale units, respectively. Fifteen minutes after MCA occlusion, overall brain pHi and cortical blood flow of the ischemic penumbra measured 6.61 +/- 0.06 and 31.9 +/- 9.2 mL/100 g per minute. Over 3 hours there was normalization of pHi in the majority of the penumbra due to increases in cortical blood flow. Within the ischemic penumbra acidic foci developed with an initial pHi of 6.35 +/- 0.09 and cortical blood flow of 18.0 +/- 5.7 mL/100 g per minute. These foci remained acidic with increased NADH fluorescence despite being surrounded by cortex that was recovering from ischemia. On light microscopy, these acidic foci had a mixed pattern of neuronal injury. CONCLUSIONS: Within the ischemic penumbra, acidic foci develop that do not follow a vascular distribution and have microscopic evidence of ischemic neuronal injury. This suggests that there is a cortical selective vulnerability regarding pHi regulation and these acidic foci may lead to recruitment of the ischemic penumbra into infarction.

Acidosis↗

PubMed1993

Brain pHi, cerebral blood flow, and NADH fluorescence during severe incomplete global ischemia in rabbits.

BACKGROUND AND PURPOSE: The aim of this experiment was to study the serial changes in brain intracellular pH, cerebral blood flow, and the oxidation/reduction level of intramitochondrial nicotinamide adenine dinucleotide fluorescence across the cortical surface during severe incomplete global ischemia. METHODS: Reduced nicotinamide adenine dinucleotide fluorescence and brain intracellular pH using the pH-sensitive indicator umbelliferone were measured with in vivo panoramic fluorescence imaging of the cortical surface. Cerebral blood flow was measured with the clearance of both umbelliferone and xenon-133. Fifteen minutes of severe incomplete global ischemia was produced by temporary occlusion of the innominate, left carotid, and subclavian arteries in five fasted New Zealand White rabbits. RESULTS: Baseline brain intracellular pH was homogeneous over the exposed cortex, measuring 7.00 +/- 0.02, while cerebral blood flow was 48.0 +/- 2.6 ml/100 g/min. During 15 minutes of ischemia, cerebral blood flow measured 6.3 +/- 1.8 ml/100 g/min and brain pH declined to 6.61 +/- 0.02 (p < 0.005); in addition, there were acidotic foci with pH measuring 6.40 +/- 0.10. During reperfusion, there was an initial normalization of brain intracellular pH without an alkaline shift followed by a recurrent cortical acidosis of pH 6.88 +/- 0.06. There was a heterogeneous pattern of fluorescence that increased significantly following 60 minutes of reperfusion, coinciding with a postischemic hypoperfusion. The hypoperfusion was a uniform reduction in cerebral blood flow over the brain's surface, with reductions of 42.5% and 44.2% at 30 and 45 minutes, respectively. CONCLUSIONS: During incomplete global ischemia there is a heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes that do not correlate with changes in cortical blood flow. The acidotic foci that were approximately 0.2 pH units more acidotic than the surrounding cortex may be the result of continued glucose delivery under anaerobic conditions. The degree of reduced nicotinamide adenine dinucleotide fluorescence suggests that the cortex is most vulnerable to metabolic failure after 60 minutes of reperfusion following severe incomplete global ischemia. The heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes suggest that there may be a selective vulnerability of cortical tissue to an ischemic challenge.

Animals↗

PubMed1993

Neuroprotection by corticotropin releasing factor during hypoxia in rat brain.

BACKGROUND AND PURPOSE: Corticotropin releasing factor is an endogenous neuropeptide released by the hypothalamus that activates the pituitary-adrenocortical system in response to stressful stimuli. It has been demonstrated that corticotropin releasing factor increases the excitability of hippocampal neurons in both in vitro and in vivo studies, which may contribute to neurological injury during hypoxia. The purpose of this study was to determine the effects of corticotropin releasing factor and its synthetic competitive antagonist, alpha-CRF, on neuronal synaptic recovery after a hypoxic insult using the hippocampal slice. METHODS: Wistar rat hippocampal brain slices (n = 120) were treated with various concentrations (10(-6) to 10(-11)) of corticotropin releasing factor or its synthetic antagonist during a 10-minute hypoxic episode. Extracellular recording of population spikes was used during and after the hypoxic insult to assess neuronal recovery. RESULTS: Corticotropin releasing factor provided dose-dependent neuronal protection with maximum recovery (37.95 +/- 8.71%) occurring at 10(-9) concentrations. The competitive antagonist alpha-CRF provided a similar degree of recovery at 10(-6) concentration, whereas 10(-9) molar concentration of competitive antagonist resulted in 16.84 +/- 7.68% recovery. CONCLUSIONS: Corticotropin releasing factor provides moderate protection to hypoxic hippocampal neurons in the brain slice preparation. The mechanism of action is unknown but appears to be a direct neuronal effect. These results support the hypothesis that corticotropin releasing factor may act as an endogenous neuroprotective hormone during hypoxia.

Animals↗

PubMed1993

MRI hippocampal volumes and memory function before and after temporal lobectomy.

We investigated the relationship between preoperative MRI hippocampal volumes and clinical neuropsychological memory test data obtained before and after temporal lobectomy and amygdalohippocampectomy for intractable epilepsy in 44 left (LTL) and 36 right (RTL) temporal lobectomy patients. In LTL patients, the difference (right minus left hippocampal volume) between hippocampal volumes (DHF) was significantly (p < 0.001) correlated (r = 0.61) with postoperative verbal memory change as measured by a delayed memory percent retention score from the Wechsler Memory Scale-Revised, Logical Memory subtest. DHF was also positively associated with postoperative memory for abstract geometric designs in LTL patients (r = 0.49, p < 0.005). Resection of a relatively nonatrophic left hippocampus was associated with poorer verbal and visual memory outcome. In RTL patients, larger right adjusted (for total intracranial volume) hippocampal volume was associated with decline in visual-spatial learning, but not memory, following surgery. MRI hippocampal volume data appear to provide meaningful information in evaluating the risk for memory impairment following temporal lobectomy.

Adult↗

PubMed1993

A retrospective analysis of pituitary apoplexy.

Thirty-seven patients with pituitary apoplexy were analyzed with an emphasis on clinical presentation and visual outcome. Their mean age was 56.6 years, with a male to female ratio of 2:1. Presenting symptoms included headache (95%), vomiting (69%), ocular paresis (78%), and reduction in visual fields (64%) or acuities (52%). Computed tomographic scanning correctly identified pituitary hemorrhage in only 46% of those scanned. Thirty-six patients underwent transsphenoidal decompression. By immunostaining criteria, null-cell adenomas were the most frequent tumor type (50%). Long-term steroid or thyroid hormone replacement therapy was necessary in 82% and 89% of patients, respectively. Long-term desmopressin therapy was required in 11%, and 64% of the male patients required testosterone replacement therapy. Surgery resulted in improvement in visual acuity deficits in 88%, visual field deficits in 95%, and ocular paresis in 100%. Analysis of the degree of improvement in preoperative visual deficits with the timing of the surgery demonstrated that those who underwent surgery within a week of apoplexy had significant recovery in their visual acuities. In the stable, conscious patient with residual vision in each eye, surgical decompression should be performed as soon as possible, because delays beyond 1 week may retard the return of visual function.

Adenoma↗

PubMed1993

Pulsatile increases in aneurysm size determined by cine phase-contrast MR angiography.

The internal flow dynamics were assessed in 16 cerebral aneurysms by cine phase-contrast magnetic resonance (MR) angiography. Six of the aneurysms were associated with subarachnoid hemorrhage and 10 were unruptured. The ruptured aneurysms demonstrated a 51% +/- 10% increase in volume between systole and diastole, while the increase in volume of the unruptured aneurysms was 17.6% +/- 8.9% (p < 0.005). The ruptured aneurysms demonstrated an approximate 1.0- to 1.5-mm increase in diameter in at least one dimension during systole. There was no relationship between aneurysm size and volumetric increases. These findings suggest that cine phase-contrast MR angiography can detect structural weakness in the aneurysmal wall. Imaging techniques that can evaluate aneurysmal wall dynamics may be useful in therapeutic planning.

Adult↗

PubMed1992

Panoramic imaging of brain pHi and CBF during penicillin and metrazole induced status epilepticus.

Using real-time in vivo umbelliferone fluorescent imaging, cortical intracellular brain pH (pHi) and cortical blood flow (CBF) were measured in New Zealand white rabbits during generalized seizures induced by intravenous metrazole or sodium penicillin. In the former, brain pHi declined from 7.04 +/- 0.07 to 6.78 +/- 0.07 within 15 min of generalized seizures and remained at this level for 1 h. In the penicillin group, pHi fell from 7.05 +/- 0.10 to 6.81 +/- 0.07 and also remained at this level over 60 min. This brain acidosis was uniform across the brain's surface. With the onset of status epilepticus there was a hyperemia which occurred in a heterogeneous pattern with blood flow appearing to be greater adjacent to cortical vasculature and slower in border zones between surface blood vessels. In the metrazole group, there was evidence of vasomotor paralysis with loss of autoregulation involving both cortical surface vasculature and penetrating arterioles with their capillary beds.

Animals↗

PubMed1992

Focal cortical distribution of blood flow and brain pHi determined by in vivo fluorescent imaging.

A technique was developed for panoramic imaging of intracellular focal brain pH (pHi) and focal cortical blood flow to measure the pattern of changes in these parameters during arterial PCO2 (PaCO2) and arterial PO2 (PaO2) alterations. Eleven overnight-fasted New Zealand White rabbits were operated and studied under 2.0 and 1.0% halothane anesthesia, respectively. The exposed cortex was imaged by a 512 x 512 pixel image intensifier system with a resolution of 10 microns2/pixel. Focal brain pHi and focal cortical blood flow were measured by umbelliferone fluorescence. The mean focal cortical blood flow was 49 +/- 4.5 ml.100 g-1.min-1, and focal brain pHi was 7.05 +/- 0.02 during normocapnia. At a stable PaCO2, focal cortical blood flow and focal brain pHi within 10 microns of surface-conducting vessels were 2-50% greater and 0.02 pH units lower than that observed in the border-zone regions between vessels. Focal cortical blood flow demonstrated a significant heterogeneity of 51% among various cortical regions, despite a stable PaCO2. Alternatively, focal brain pHi was homogeneous, varying no more than 0.05 pH units. These results demonstrate the dependence of focal cortical blood flow on topical locations from surface conducting vessels and the tight regulation of brain pHi.

Animals↗

PubMed1992

Medulloblastoma: I. Clinical, diagnostic, and therapeutic overview.

Medulloblastoma, the most common embryonal tumor of the central nervous system, affects both children and adults. It poses a significant therapeutic challenge in that age-dependent differences exist, not only in their pathobiology, but in the efficacy of chemotherapy and radiotherapy. This is particularly the case in very young children, whose still developing nervous system exhibits a low tolerance to radiotherapy. We review the epidemiology, clinical presentation, radiologic features, and current therapeutic concepts relative to this unique neoplasm. Efforts are made to highlight clinical controversies.

Adolescent↗