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a Clinical
Neuroscience, St George's Hospital Medical School, Cranmer Terrace,
London, SW17 ORE, UK, b Neuroimaging
Guy's, King's, and St Thomas' School of Medicine and the Institute
of Psychiatry
Correspondence to: : Professor H Markus, Clinical Neuroscience h.markus{at}sghms.ac.uk
Received 21 August
2000 and in revised form 12 February 2001;
Accepted 16
February 2001
OBJECTIVES
Better
methods of identifying patients with asymptomatic carotid artery
stenosis who are at high risk of stroke are required. It has been
suggested that proton magnetic resonance spectroscopy (MRS) may allow
the identification of ongoing ischaemia in this patient group by the
detection of a potentially reversible reduction of N-acetyl aspartate
(NAA), a presumed marker of neuronal integrity, and the presence of
lactate, a marker of anaerobic metabolism. Previous studies have
reported metabolite ratios rather than absolute concentrations. This
study was performed to determine if NAA was reduced ipsilateral to
carotid stenosis or occlusion, and if its concentration was related to
carbon dioxide reactivity, a marker of cerebrovascular reserve.
METHODS Twenty one
patients with unilateral carotid stenosis (>70%) or occlusion were
studied. Single voxel proton MRS was performed in the ipsilateral and
contralateral hemispheres, with the voxel positioned in the arterial
borderzone region between the middle and anterior cerebral artery
territories. Absolute quantification of metabolite concentrations was
performed. Cerebrovascular reactivity to 6% carbon dioxide was
determined in both middle cerebral artery territories using
transcranial Doppler ultrasonography.
RESULTSMean (SD)
cerebrovascular reactivity was significantly lower in the stenosed
compared with the contralateral hemisphere (13.3 (7.7)
v 19.2 (8.2)%/kPa, p=0.002). There were no
significant differences in the absolute concentrations of NAA, choline,
or creatine between the ipsilateral and contralateral hemispheres (for
example, NAA 10.1 (1.1) v 10.5 (1.1) mmol/l, p=0.1). No lactate peak
was seen in any spectra. For each metabolite measured, there was no
correlation between the absolute concentration and cerebrovascular
reactivity for either hemisphere.
CONCLUSIONSIn
patients with carotid stenosis and occlusion we found no evidence that
chronic hypoperfusion is associated with a reduction in NAA or the
presence of lactate. Magnetic resonance spectroscopy is unlikely to
help in the selection of patients with asymptomatic carotid stenosis
for endarterectomy.
This article has been cited by other articles:
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  F. C. Bakker, C. J.M. Klijn, J. van der Grond, L. J. Kappelle, and A. Jennekens-Schinkel Cognition and quality of life in patients with carotid artery occlusion: A follow-up study Neurology, June 22, 2004; 62(12): 2230 - 2235. [Abstract] [Full Text] [PDF]
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 D.R. Rutgers, M.J.P. van Osch, L.J. Kappelle, W.P.T.M. Mali, and J. van der Grond Cerebral Hemodynamics and Metabolism in Patients With Symptomatic Occlusion of the Internal Carotid Artery Stroke, March 1, 2003; 34(3): 648 - 652. [Abstract] [Full Text] [PDF]
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