Illustrated Encyclopedia of Human Anatomic Variation: Opus II: Cardiovascular System: Arteries: Head, Neck, and Thorax

External Carotid Artery

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

It may be absent unilaterally or bilaterally. When unilaterally absent, the branches usually derived from it arise from the upward continuation of the common trunk or from the contralateral vessel. The artery is sometimes located superficially, and runs lateral to the stylohyoid muscle or between the posterior belly of the digastric muscle and the stylohyoid.

The branches of the external carotid may arise irregularly or be diminished or increased in number. When increased in number (by two or more), they arise as a common stem or by the addition of branches not usually derived from this artery, such as a sternomastoid branch of either the superior thyroid or occipital artery. On occasion, all the branches arise close together from a common point just above the origin of the artery from the common carotid.

The external carotid may provide an accessory superior thyroid, a dorsal lingual, an accessory ascending pharyngeal.

A curious variation is an external carotid composed of two separate trunks that unite behind the condylar process of the mandible forming an anulus, from which the various branches arise.

Variations in some of the branches of the external carotid are as follows: The ascending pharyngeal may arise from the external carotid or the bifurcation of the common carotid (65-80%), the occipital (14-20%), or the common carotid (7-9%). The lingual arises from a common trunk with the facial (linguofacial trunk) in 10-20% of cases; a rare combination branch of the external carotid is a thyrolinguofacial trunk. The sternocleidomastoid, usually a branch of the superior thyroid, may arise as an independent branch of the external carotid.

Image 112, Image 288, Image 437

References

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