Vertebrobasilar insufficiency (VBI) describes a temporary set of symptoms due to decreased blood flow (ischemia) in the posterior circulation of the brain. The posterior circulation supplies the medulla, pons, midbrain, cerebellum and (in 70-80% of people) supplies the posterior cerebellar artery to the thalamus and occipital cortex. As a result, symptoms vary widely depending which brain region is predominantly affected. The term 'vertebrobasilar insufficiency' may be used to describe disease in the vertebral and basilar arteries which predisposes to acute embolic events such as transient ischemic attacks (TIAs) and stroke. Alternatively it may be used to describe recurrent symptoms which result from narrowing (stenosis) of these arteries in combination with changes of blood pressure or head position. VBI should not be confused with other conditions which may relate to the posterior circulation. 25% of strokes and TIAs affect parts of the brain supplied by the posterior circulation, but many of these are embolic from cardiac or other sources. VBI should also not be confused with beauty parlour syndrome which refers to strokes caused by acute arterial dissection brought on by extreme head positions, such as those maintained during hair washing. Signs and symptoms Symptoms relate to impaired brain function in areas supplied by the posterior circulation, as seen in posterior circulation strokes. However, symptoms may be far briefer than those seen in stroke. Vertigo is a relatively common symptom that can result from ischemia to the cerebellum, medulla or (rarely) the internal auditory artery which supplies the vestibular system of the inner ear. While vertigo is a common feature of VBI or posterior circulation stroke, VBI only rarely presents with vertigo alone (without other neurological signs). Pathology VBI results from narrowing of posterior circulation arteries, known as stenosis. The most common cause of arterial stenosis is atherosclerosis, however other pathologies such as fibromuscular dysplasia, dissection, trauma or external compression may occur. Atherosclerotic plaque can rupture, resulting in a source of emboli. These emboli can cause TIAs or strokes in the areas of the brain supplied by the affected artery. Where stenosis is severe, abrupt changes in blood pressure can temporarily result in inadequate flow through the stenosis, causing symptoms that are usually very brief. A common cause is orthostatic hypotension which results in a fall in blood pressure when the patient changes posture and may be exacerbated by medicines (particularly antihypertensives), dehydration and heat. In reality, orthostatic hypotension can cause