title: Duplicate origin and fenestration of the middle cerebral artery on MR angiography.
abstract: BACKGROUND
  Duplicate origin of the middle cerebral artery (MCA) is rare and has been misdiagnosed or confused as fenestration of the proximal M1 segment of the MCA. The condition is not a true fenestration and occurs when two MCA branches arise separately from the terminal segment of the internal carotid artery, and fuse to form an arterial ring. We researched our institutional records to determine the prevalence of such cases and investigated its characteristic features on magnetic resonance (MR) angiography.
  
  
  METHODS
  To isolate these cases, we retrospectively reviewed cranial MR angiographic images of 3,491 patients obtained on either of two 1.5-tesla scanners at our institution from April 1, 2007 through December 31, 2009.
  
  
  RESULTS
  We found four cases of duplicate origin of the MCA, two cases each on the right and the left (3 men, one woman), representing a prevalence of 0.11%. All four arterial rings were small and mimicked fenestration of the proximal M1 segment. During the same period, we found three MCA fenestrations, two at the proximal M1 segment and one at the middle M1 segment. Total prevalence of duplicate origin and fenestration was 0.20%.
  
  
  CONCLUSIONS
  In our institution, we observed 0.11% prevalence of duplicate origin of the MCA on MR angiography, and all were small and mimicked fenestration. Clinically, an important difference between duplicate origin and fenestration of the MCA is the potential collateral circulation available from the inferior branch in the case of saddle embolism occlusion of only the superior branch when there is duplicate origin of the MCA.
authors.affiliation: Department of Diagnostic Radiology, Saitama Medical University International Medical Center, 1397-1 Yamane, Hidaka, Saitama, Japan. auchino@saitama-med.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Uchino
authors.forename: Naoko
authors.initials: N
authors.lastname: Saito
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Okada
authors.forename: Reiko
authors.initials: R
authors.lastname: Nakajima
mesh_terms: D000328:Adult; D002533:Cerebral Angiography; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000002:abnormalities*; D012189:Retrospective Studies