We present a case of a 43-year-old female with headaches, progressive paresthesias of the upper extremities, and vertigo. Ultrasonography could not visualize the left internal carotid artery (ICA). Magnetic resonance imaging (MRI) showed complete fusion of the C5, C6, and C7 levels, representing Klippel-Feil deformity. Angiography showed a unique abnormality of the aortic arch with complete absence of the left ICA. An embryologic defect associated with this type of abnormality is proposed, with defects of development of the third aortic arch and the aortic sac secondarily.
