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Disease Profile

Internal carotid agenesis

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

<1 / 1 000 000

US Estimated

Europe Estimated

Age of onset

All ages





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Agenesis of the internal carotid artery; Internal carotid artery agenesis


Blood Diseases; Congenital and Genetic Diseases; Nervous System Diseases


Internal carotid agenesis occurs when one or both of the blood vessels that supply blood to the brain (internal carotid arteries) do not develop (agenesis). The missing carotid artery can be on either side of the body. People missing one or both of the internal carotid arteries may not have any symptoms, because the body develops other blood vessel pathways to carry blood to the head.[1][2][3] Some people do have symptoms including headaches, blurred vision, paralysis of some of the nerves in the head (palsy), recurrent seizures (epilepsy), or muscle weakness on one side of the body (hemiparesis).[2][3] People who have internal carotid agenesis have an increased risk for enlargement of the other blood vessels (aneurysm) in the brain.[1][2][3]

The exact cause of internal carotid agenesis is not known.[4] Diagnosis of internal carotid agenesis often occurs accidentally when a person is having a brain MRI or CT scan. The diagnosis can be confirmed with magnetic resonance angiography (MRA). Due to a higher risk of brain aneurysms seen in people who have internal carotid agenesis, screening for aneurysms may be recommended. In some cases, surgery may be necessary to treat symptoms caused by internal carotid agenesis.[1][2][3]


Internal carotid agenesis occurs when one or both of the blood vessels that supply blood to the brain (internal carotid artery) do not form (agenesis). Internal carotid agenesis does not always cause symptoms because the body uses other blood vessels (collateral pathways) to carry the blood to the brain.[1][2][3] However, some people may have symptoms such as headaches, blurred vision, paralysis of some of the nerves in the head (palsy), recurrent seizures (epilepsy), or muscle weakness on one side of the body (hemiparesis).[2][3]

Some people with internal carotid agenesis may have other malformations involving the blood vessels, face, or ears. This typically occurs on the same side of the body as the internal carotid agenesis.[5] People who have internal carotid agenesis are at an increased risk to develop an enlargement of other blood vessels in the brain (aneurysm). The risk for people with internal carotid agenesis to develop a brain aneurysm is estimated at 24-34%.[1][2][3]

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
30%-79% of people have these symptoms
Cerebral ischemia
Disruption of blood oxygen supply to brain
Dilatation of the cerebral artery
Subarachnoid hemorrhage
5%-29% of people have these symptoms
Arachnoid cyst
Fluid-filled sac located in membrane surrounding brain or spinal cord


The cause of internal carotid agenesis is currently unknown. The malformation is present from birth and is believed to be caused when something happens early during the development of the baby that stops the carotid artery from forming correctly. Most of the time, the malformation is thought to occur by chance. However, less commonly, a person with internal carotid agenesis may also have other diseases or syndromes. People with internal carotid agenesis caused by other syndromes typically have other symptoms or medical problems.[1][2][3]


Internal carotid agenesis is diagnosed when one or both of the internal carotid arteries are found to be missing by specific imaging tests. These imaging tests may include angiography, computed tomography scanning (CT scan), and magnetic resonance imaging (MRI). These tests are used to visualize the blood vessels and the surrounding bones. The diagnosis may be confirmed with another imaging test called magnetic resonance angiogram (MRA) that looks specifically at the blood vessels. If people who have internal carotid agenesis do not have symptoms of the malformation, it is typically diagnosed by accident (or incidentally) when evaluating for other health concerns.[1][2][3]


Internal carotid agenesis may not require any treatment if there are no symptoms. However, since the blood is rerouted through other smaller blood vessels to supply blood to the brain, these blood vessels may develop problems due to the extra blood flow. In some cases, surgery may be an option to relieve symptoms.[1][2][3]

Due to the increased risk of aneurysms, many doctors recommend that a person with internal carotid agenesis be screened for the development of aneurysms. However, the condition is rare, it is not clear how often such screening should take place and if screening is actually helpful. If a brain aneurysm is observed, further monitoring or surgery may be necessary.[1][2][3]


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Providing General Support

    Learn more

    These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

    In-Depth Information

    • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
    • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
    • PubMed is a searchable database of medical literature and lists journal articles that discuss Internal carotid agenesis. Click on the link to view a sample search on this topic.


      1. Okawa M, Higashi T, Komiyama M, Fukuda K, Abe H, Inoue T. Left internal carotid artery agenesis with trans-sellar collateral and a right aortic arch: Case report. Interventional Neuroradiology. December 2015; 21(6):759-764. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4757351.
      2. Oz II, Serifoglu I, Yazgan O, Erdem Z. Congenital absence of internal carotid artery with intercavernous anastomosis: Case report and systematic review of the literature. Interventional Neuroradiology. August 2016; 22(4):473-480. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4984390.
      3. Oliveira GdP; Soares NLR; Oliveira GdP , Vale BP. Bilateral internal carotid artery agenesis: a case report. J Vasc Bras. October/December 2014; 13(4):336-339. https://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-54492014000400336.
      4. Internal carotid agenesis. Orphanet. https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=981. Accessed 9/23/2017.
      5. Lee JH, Oh CW, Lee SH, and Han DH. Aplasia of the internal carotid artery. Acta Neruochir. February 2003; 145(2):117-125. https://www.ncbi.nlm.nih.gov/pubmed/12601459.
      6. Singer RJ, Ogilvy CS, Rordorf G. Screening for intracranial aneurysm. UpToDate. November 7, 2016; https://www.uptodate.com/contents/screening-for-intracranial-aneurysm.
      7. Ohtani T, Iijima K, Aishima K, Wada H, Sasaguchi N, and Kurihara H. Segmental Aplasia of Bilateral Internal Carotid Arteries Accompanied by Intracranial Aneurysms: A Case Report. NMC Case Report Journal. July 2017; 4(3):67-69. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5566686/.
      8. Kumaresh A, Kumar Vasanthraj P, and Chandrasekharan A. Unilateral Agenesis of Internal Carotid Artery with Intercavernous Anastamosis: A Rare Case Report. Journal of Clinical Imaging Science. 2015; 5:7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4322372/.
      9. Dinc H, Alioglu Z, Erdol H, and Ahmetoglu A. Agenesis of the internal carotid artery associated with aortic arch anomaly in a patient with congenital Horner’s syndrome. American Journal of Neuroradiology. June 2002; 23(6):929-931. https://www.ajnr.org/content/23/6/929.long.

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