title: Radiological reasoning: extracranial causes of unilateral decreased brain perfusion.
abstract: OBJECTIVE
  A 50-year-old man presented with neurologic symptoms and upper extremity claudication associated with exercise. Perfusion MRI of the brain showed delayed time-to-peak in the right cerebral hemisphere, and MR angiography (MRA) of the circle of Willis showed decreased flow-related enhancement in the right internal carotid artery and its branches. Neck MRA showed occlusion of the right innominate (brachiocephalic) artery and retrograde flow in the ipsilateral vertebral artery. On the basis of this clinical scenario, we discuss the radiologic evaluation of unilateral decreased brain perfusion, which, in this case, was due to an occlusion of the innominate artery with resultant innominate steal.
  
  
  CONCLUSIONS
  In the absence of an explanatory intracranial stenosis, the finding of unilateral decreased cerebral perfusion on MRI or CT mandates evaluation of the aortic arch and cervical arteries to determine a level and cause of occlusion. Severe stenoses may be associated with steal phenomena, which can be diagnosed with MRA or Doppler sonography.
authors.affiliation: Department of Radiology, University of North Carolina at Chapel Hill, CB #7510, 101 Manning Drive, Chapel Hill, NC 27599-7510, USA. bhuang@unch.unc.edu
authors.forename: Benjamin Y
authors.initials: BY
authors.lastname: Huang
authors.forename: Mauricio
authors.initials: M
authors.lastname: Castillo
mesh_terms: D001157:Arterial Occlusive Diseases / Q000150:complications* / Q000175:diagnosis* / Q000628:therapy; D016122:Brachiocephalic Trunk; D006801:Humans; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D013349:Subclavian Steal Syndrome / Q000175:diagnosis / Q000209:etiology* / Q000628:therapy