title: Type 2 proatlantal intersegmental artery associated with persistent trigeminal artery diagnosed by MR angiography.
abstract: OBJECTIVE
  The type 2 proatlantal intersegmental artery (PIA) is a rare anastomosis between the external carotid artery (ECA) and vertebral artery (VA) that passes through the foramen magnum. The persistent trigeminal artery (TA) is the most common anastomosis between the internal carotid artery (ICA) and basilar artery. The purpose of this paper is to present the first case of a type 2 PIA associated with an ipsilateral persistent TA diagnosed using magnetic resonance (MR) angiography, and we briefly discuss the embryology of this rare anomaly.
  
  
  METHODS
  An 83-year-old man with cerebral infarctions underwent cerebral MR imaging, and head and neck MR angiography using a 1.5 T imager. MR angiography was obtained using the standard non-contrast three-dimensional time-of-flight technique.
  
  
  RESULTS
  MR angiography showed aplasia of the proximal left VA and a large anastomotic artery between the left ECA and distal left VA that passed through the foramen magnum, indicative of a type 2 PIA. This patient also had an anastomosis between the precavernous segment of the left ICA and midbasilar artery via a lateral course, indicative of a lateral-type persistent TA.
  
  
  CONCLUSIONS
  We present the first case of type 2 PIA associated with ipsilateral lateral-type persistent TA diagnosed by MR angiography. MR angiography should be performed including the carotid bifurcation to find more frequently extracranial arterial variations, including type 2 PIAs.
authors.affiliation: Department of Diagnostic Radiology, Saitama Medical University International Medical Center, 1397-1 Yamane, Hidaka, Saitama, 350-1298, 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: Kaiji
authors.initials: K
authors.lastname: Inoue
mesh_terms: D000369:Aged, 80 and over; D002342:Carotid Artery, External / Q000002:abnormalities* / Q000473:pathology*; D002544:Cerebral Infarction / Q000175:diagnosis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D014711:Vertebral Artery / Q000002:abnormalities* / Q000473:pathology*