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AJNR Awards, New Junior Editors, and more. Read the latest AJNR updates

Case of the Month

Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO

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February 2017
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Next Case of the Month coming March 7 …

Agenesis of Internal Carotid Artery

  • Background:
    • Internal carotid artery agenesis, hypoplasia, and aplasia are rare congenital anomialies occuring in only 0.01% of the general population.
    • Agenesis of internal carotid artery increases the risk of developing aneurysms due to increased flow through the collateral arteries.
    • Major collateral circulation may be recruited from the circle of Willis, embryonic vessels, or transcranial collaterals from the external carotid artery (ECA).
  • Clinical Presentation:
    • Patients may be asymptomatic or present with decreased visual acuity, unilateral weakness and numbness, slurred speech, headache, and drowsiness.
    • Agenesis of internal carotid artery may occur as a component of PHACE syndrome.
  • Key Diagnostic Features:
    • Lack of ICA enhancement associated with absence of the petrous carotid canal within the skull base
    • Abnormal ECA or collateral arteries are demonstrated on common carotid artery angiography.
  • Differential Diagnosis:
    • Internal carotid artery thrombosis
    • ICA stenosis
    • Moyamoya disease
    • ICA vasospasm

Suggested Reading

  1. Given CA II, Huang-Hellinger F, Baker MD, et al. Congenital absence of the internal carotid artery: case reports and review of the collateral circulation. AJNR Am J Neuroradiol 2001;22:1953–59
  2. Weon Y-C, Chung J-I, Kim H-J, et al. Agenesis of bilateral internal carotid arteries and posterior fossa abnormality in a patient with facial capillary hemangioma: presumed incomplete phenotypic expression of PHACE syndrome. AJNR Am J Neuroradiol 2005;26:2635–39
  3. Nicoletti G, Sanguigni S, Bruno F, et al. Hypoplasia of the internal carotid artery: collateral circulation and ultrasonographic findings. A case report. Journal of Ultrasound 2009;12:41–4, 10.1016/j.jus.2008.12.003

Current Issue

American Journal of Neuroradiology: 46 (6)
American Journal of Neuroradiology
Vol. 46, Issue 6
1 Jun 2025
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Print ISSN: 0195-6108 Online ISSN: 1936-959X

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