Bilateral persistence of type 1 proatlantal arteries: report of a case and review of the literature.

Persistent proatlantal artery type 1 is one of the four anastomotic vessels between the carotid and vertebrobasilar arterial systems. Persistence of this embryonic anastomosis is extremely rare. We present such a case with bilateral persistent proatlantal arteries that arose from internal carotid arteries, entered the skull via the foramen magnum and united with the horizontal portions of vertebral arteries. We also mention its embryology, potential clinical implications, and differentiating features between two types of proatlantal arteries.