Bilateral concurrent type I and type II persistent proatlantal arteries: A case report.

Transient embryonic carotid-vertebrobasilar anastomoses can intermittently persist beyond the embryonic period. These vascular anomalies are often serendipitously identified during evaluation for unrelated disease states and pathologies. The persistent proatlantal intersegmental artery is one such recognized rare fetal anastomotic connection, often arising unilaterally. Bilateral persistence of the proatlantal anastomosis is a rarer occurrence, seldom described in the literature. We report a case of bilateral concurrent type I and type II proatlantal arteries, describe the embryology of persistent carotid-vertebrobasilar anastomoses, and consider pertinent clinical implications.