Rotational vertebrobasilar insufficiency, or bow hunter's syndrome, is a rare 
cause of posterior circulation ischemia, which, following rotation of the head, 
results in episodic vertigo, dizziness, nystagmus, or syncope. While typically 
caused by dynamic occlusion of the vertebral artery in its V2 and V3 segments, 
the authors here describe a patient with dynamic occlusion of the vertebral 
artery secondary to a persistent first intersegmental artery, a rare variant 
course of the vertebral artery. In this case the vertebral artery coursed under 
rather than over the posterior arch of the C-1. This patient was also found to 
have incomplete development of the posterior arch of C-1, as is often seen with 
this variant. The patient underwent dynamic digital subtraction angiography, 
which demonstrated occlusion at the variant vertebral artery with head turning. 
He was then taken for decompression of the vertebral artery through removal of 
the incomplete arch of C-1 that was causing the dynamic compression. After 
surgery the patient had a complete resolution of symptoms. In this report, the 
authors present the details of this case, describe the anatomical variants 
involved, and provide a discussion regarding the need for atlantoaxial fusion in 
these patients.