title: Bilateral Internal Carotid Artery Segmental Agenesis: Embryology, Common Collateral Pathways, Clinical Presentation, and Clinical Importance of a Rare Condition.
abstract: BACKGROUND
  Bilateral segmental agenesis of the internal carotid artery is a rare congenital anomaly. We present a case of bilateral internal carotid artery segmental agenesis in an asymptomatic 18-year-old man. Embryology, common collateral pathways, clinical presentation, and clinical importance of this condition are discussed. According to our review of the literature, this report is the first to describe bilateral internal carotid artery segmental agenesis in a patient studied with magnetic resonance imaging, computed tomography, Doppler ultrasonography, and digital subtraction angiography.
  
  
  METHODS
  An 18-year-old man presented to our hospital complaining of occasional mild headaches. Neurologic examination was unremarkable. Imaging findings consisted of bilateral segmental agenesis of the internal carotid arteries.
  
  
  CONCLUSIONS
  Bilateral segmental agenesis of internal carotid artery may be completely asymptomatic and harmless, but associated conditions, such as cerebral aneurysms or abnormal collateral circulation, should alert clinicians to the possibilities of subarachnoid hemorrhage or cerebral ischemia.
authors.affiliation: Radiodiagnostica e Neuroradiologia, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy. Electronic address: andrea.alexandre@libero.it.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Alexandre
authors.affiliation: Radiodiagnostica e Neuroradiologia, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy.
authors.forename: Emiliano
authors.initials: E
authors.lastname: Visconti
authors.affiliation: Radiodiagnostica e Neuroradiologia, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Schiarelli
authors.affiliation: Radiodiagnostica e Neuroradiologia, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Frassanito
authors.affiliation: Radiodiagnostica e Neuroradiologia, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pedicelli
mesh_terms: D000293:Adolescent; D015901:Angiography, Digital Subtraction; D002343:Carotid Artery, Internal / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000196:embryology; D020785:Central Nervous System Vascular Malformations / Q000000981:diagnostic imaging* / Q000196:embryology; D002533:Cerebral Angiography; D003097:Collateral Circulation; D006801:Humans; D021621:Imaging, Three-Dimensional; D018810:Magnetic Resonance Angiography; D008279:Magnetic Resonance Imaging; D008297:Male; D035583:Rare Diseases; D014057:Tomography, X-Ray Computed; D018608:Ultrasonography, Doppler
keywords: Absence of the internal carotid artery; Doppler ultrasonography; Internal carotid artery; Internal carotid artery hypoplasia; Internal carotid artery malformations; Internal carotid artery segmental agenesis; Rete mirabile