<unk>  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 vague symptoms (e.g. dizziness) which are similar to those caused by<unk> ;<unk>  should only be considered where the stenosis is severe and/or there are focal neurological symptoms specific to the posterior circulation.<unk>  may also result from altered blood flow as seen in subclavian steal syndrome.<unk>  is described as a cause of symptoms that occur with changes to head position. Rotational vertebral artery syndrome (sometimes referred to as Bow Hunter's Syndrome) results from vertebral artery compression on rotating the neck. The commonest cause is a bone spur from a cervical vertebra, in combination with disease in the opposite vertebral artery. Rotational vertebral artery syndrome is rare.
Vertebrobasilar insufficiency
Convergence insufficiency
Velopharyngeal insufficiency
Eustachian tube dysfunction
Noise-induced hearing loss
Vibroacoustic disease
Aqueductal stenosis
Subglottic stenosis