CAROTID CIRCULATION

The common carotid arteries ascend within both sides of the neck. They are invested by a condensation of the deep layer of the cervical fascia (carotid sheath) along with the internal jugular vein and vagus nerve (cranial nerve X). The carotid sheath structures are deep to the sternocleidomastoid muscle. The common carotid artery (CCA) lies medial to the internal jugular vein. At the C3-4 (34 %) or C4-5 (46 %) level the common carotid artery bifurcates into the external carotid artery (ECA) and the internal carotid artery (ICA). The bifurcation can occur as high as C1 or as low as T2. The proximal internal carotid artery most often lies postero-lateral to the proximal external carotid artery and medial to the internal jugular vein. The internal carotid artery ascends almost vertically in the neck and enters the skull base through an aperture within the petrous bone called the carotid canal. There are no major named branches of the ICA within the neck. Rarely one may encounter takeoff of an occipital or other normal branch of the ECA from an otherwise normal ICA.

After arising from the common carotid artery, the external carotid artery travels in a tortuous course within the deep spaces of the upper neck/face and gives rise to multiple branches that supply the face, scalp, major portions of the dura, and upper pole of the thyroid gland.