The primitive trigeminal, otic, hypoglossal, and proatlantal intersegmental
arteries are fetal anastomoses between the carotid and vertebrobasilar sys
tems, Persistent trigeminal artery (PTA) is the most frequent embryonic com
munication between the vertebrobasilar and carotid systems in adults. We re
port a case of PTA compressing the left side of the pituitary gland and sta
rk, in a patient with elevated blood prolactin level.