vague symptoms (e.g. dizziness) which are similar to those caused by VBI; VBI should only be considered where the stenosis is severe and/or there are focal neurological symptoms specific to the posterior circulation. VBI may also result from altered blood flow as seen in subclavian steal syndrome. VBI 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. Diagnosis The diagnosis of posterior circulation stroke or TIA can be made on the basis of history and physical examination, which should include exclusion of alternative causes for the patient's symptoms and consideration of risk factors for atherosclerosis. To confirm VBI, imaging studies of the posterior circulation can be performed. CT is often the first study performed in acute stroke or TIA, as it is effective at excluding intracranial haemorrhage, however MRI is better at detecting ischemic strokes in the posterior distribution. CT angiography and Magnetic Resonance Angiography (MRA) can be used to detect atherosclerosis and other diseases in the posterior circulation arteries. Both can over-estimate stenosis. It is also important to remember that atherosclerosis is a common finding, and its presence does not confirm that this was the cause of the patient's symptoms. Alternative diagnoses VBI is often considered when a patient complains of dizziness. It is important to distinguish dizziness caused by vertigo from the sensation of being light-headed, as the latter is more commonly a result of other conditions. Brief episodes of vertigo brought on by head movements are more likely to be Benign paroxysmal positional vertigo. Alternatively, carotid sinus hypersensitivity can cause episodes of dizziness and collapse on head turning if the neck brushes against clothing. Treatment The main treatment for VBI is to address risk factors for atherosclerosis such as smoking, hypertension and diabetes. Patients are often started on an antiplatelet (e.g. aspirin, clopidogrel) or occasionally an anticoagulant (e.g. warfarin) to reduce the risk of future strokes. Where VBI is causing reproducible symptoms due to stenosis, lifestyle modification to avoid provoking factors (e.g. dehydration, standing rapidly from sitting or lying) may reduce symptoms. Open surgical repair or stenting can be performed to re-open stenosed vertebral arteries, and