Characterized by diminished blood flow through the vertebral or basilar arteries
The two vertebral arteries originally branch proximally from subclavian, travel through vertebrae, and distally join to become basilar artery
Symptoms result from diminished circulation to the posterior brain, brainstem and cerebellum.
Head-turning can cause ipsilateral vertebral artery to temporarily occlude
If contralateral vertebral artery is stenotic, may lead to syncope (known as Bow hunter's syndrome)
Head extension may also provoke symptoms
Neurologic symptoms tend to not present when one vertebral artery remains patent
Symptoms may result secondary to arterial plaques, arterial dissection, compressive lesions, or subclavian steal (see below).  *Posterior strokes encompass 20-30% of all strokes
Cervical osteophytes can also directly compress vertebral arteries and cause<unk>  symptoms.
If contralateral vertebral artery is stenotic, may lead to syncope (known as Bow hunter's syndrome)
Head turning causes temporary occlusion of the ipsilateral vertebral artery. <unk>  results if the contralateral vertebral artery has a fixed occlusion.  Improvement of symptoms in neutral position is considered pathognomonic
Stenotic lesion in the subclavian, located proximal to the vertebral artery--> reversed flow of blood in the vertebral artery when superimposed with increased arm activity(4).
Vertebrobasilar insufficiency
Vestibular/otologic
Subglottic stenosis
Benign paroxysmal positional vertigo 
Carotid-cavernous fistula
Traumatic 
Sinus barotrauma
Infection