Proatlantal intersegmental artery

Case contributed by Dr Eric F Greif


Known nasopharyngeal squamous cell carcinoma.

Patient Data

Age: 65 years
Gender: Female

Incidentally noted is a carotid-basilar anastomotic vessel arising from the left external carotid artery at the level of the 2nd cervical vertebral body (C2). The vessel courses dorsally and joins the left vertebral artery in the suboccipital space, with artery then entering the foramen magnum.  

There is a heterogenous solid right nasopharyngeal soft tissue mass partially filling the nasopharyngeal and oropharyngeal airway and slightly crossing the midline leftward. This is consistent with patients known squamous cell carcinoma.  

There is a persistent carotid-vertebrobasilar anastomoses arising from the left external carotid artery consistent with a type 2 proatlantal intersegmental artery.  

The aberrant artery arises from the left external carotid artery at the level of C2, with the vessel then coursing dorsally and joining with the left horizontal vertebral artery in the suboccipital space, which then enters the foramen magnum (yellow arrows).

The left intracranial vertebral artery is also depicted (blue arrow).  

Case Discussion

66 year old female with history of right nasopharyngeal squamous cell carcinoma, with an incidental finding of a persistent left proatlantal intersegmental artery.

Two types of proatlantal intersegmental arteries have been described, both arising from the carotid artery and entering the foramen magnum. Type 1 proatlantal artery arises from the internal carotid artery and ascends to the level of the occipitoatlantal space without passing through the transverse foramen of any cervical vertebra. The artery takes a dorsal course cephalad to the transverse process of C1 and then travels rostrally to enter the foramen magnum. Type 2 proatlantal artery arises from the external carotid (as in this case).

The proatlantal intersegmental artery should be differentiated from a more frequently seen persistent hypoglossal artery, another type of  persistent carotid-vertebrobasilar anastomoses.


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Case information

rID: 53848
Published: 9th Jun 2017
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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