Radiographic anatomy of the extracranial carotid artery.

Only 55% of common carotid arteries bifurcate in the neck at the classically described level of C3 vertebra or C3/4 interspace. Others bifurcate as high as C2/3 interspace or as low as C5/6. Eighty-five percent of bifurcations occur at the same height as that on the contralateral side. Even if asymmetry occurs, it is not greater in magnitude than the height of one cervical vertebra. Atheroma does not appear to be associated with any particular bifurcation position. Abnormally curved or kinked morphology of the extracranial internal carotid occurs in 6% of angiograms. This feature also has no specific association with atheroma.