title: Carotid endarterectomy improves cerebrovascular reserve capacity preferentially in patients with preoperative impairment as indicated by asymmetric BOLD response to hypercapnia.
abstract: OBJECTIVE
  In patients with symptomatic carotid artery disease the predominant mechanism causing ischaemic injury is considered to be thromboembolic, however compromise of cerebral haemodynamics is considered to be a significant factor. Removal of the embolic source is accepted as the major benefit from carotid endarterectomy (CEA), however improvement in cerebral haemodynamics may be another beneficial outcome as suggested by transcranial doppler (TCD). Blood oxygen level-dependent (BOLD) hypercapnia functional magnetic resonance imaging (fMRI) can be used to map the cerebrovascular reserve (CVR). The aim of this study was to assess the effects of carotid surgery on cerebral haemodynamics in patients with carotid artery disease using a hypercapnia BOLD fMRI and assessment of hemispheric asymmetry.
  
  
  METHODS
  Seventeen patients with symptomatic internal carotid artery stenosis were scanned using a clinical 1.5T MR scanner. Scanning was done immediately prior to and between 4 and 8 weeks after CEA. 10% carbon dioxide was administered to achieve transient episodes of hypercapnia. The data was analyzed using FMRIB Software Library (FSL) software to derive percentage signal change (PSC) for the grey matter of the middle cerebral artery (MCA-GM) territory for both hemispheres. MCA-GM PSC was furthermore normalized to the contralateral hemisphere to derive an Hemispheric Asymmetry Index (hAI) for all patients pre- and postoperatively.
  
  
  RESULTS
  Ipsilateral GM CVR improved significantly following CEA (2.47% preoperatively vs. 2.73% postoperatively, p=0.038). There was no change in CVR in the contralateral grey and white matter MCA territories (p=0.27, p=0.1). Also, the hAI was significantly more shifted to the ipsilateral hemisphere after CEA (preoperative hAI -0.56, vs. -3.90 postoperatively, p=0.02). Patients with an impaired hAI preoperatively were found to show the greatest improvement in PSC and hAI following CEA (p=0.007).
  
  
  CONCLUSIONS
  CEA resulted in improved CVR in patients with carotid artery disease as shown by the absolute and hemispheric asymmetry of BOLD response to hypercapnia.. These findings show that benefits from recanalisation may go beyond removal of the embolic source, by improving the cerebrovascular reserve. Moreover, hypercapnia BOLD fMRI may be a useful clinical tool in predicting this therapeutic potential in patients with severe carotid artery disease.
authors.affiliation: Department of Academic Radiology, University of Nottingham, Queens Medical Centre, Nottingham, UK.
authors.forename: S D
authors.initials: SD
authors.lastname: Goode
authors.forename: N
authors.initials: N
authors.lastname: Altaf
authors.forename: D P
authors.initials: DP
authors.lastname: Auer
authors.forename: S T R
authors.initials: ST
authors.lastname: MacSweeney
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D002245:Carbon Dioxide; D002343:Carotid Artery, Internal / Q000503:physiopathology / Q000601:surgery*; D016893:Carotid Stenosis / Q000097:blood / Q000150:complications / Q000503:physiopathology / Q000601:surgery*; D002560:Cerebrovascular Circulation; D002561:Cerebrovascular Disorders / Q000097:blood / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D016894:Endarterectomy, Carotid; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000503:physiopathology*; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D016896:Treatment Outcome
chemical_list: D015415:Biomarkers; D002245:Carbon Dioxide; D010100:Oxygen