the femoral artery) and advancing an intravascular catheter through the aorta towards the vertebral arteries. at that point, radiocontrast is injected and its downstream flow captured on fluoroscopy (continuous x-ray imaging). the vessel may appear stenotic (narrowed, 41–75%), occluded (blocked, 18–49%), or as an aneurysm (area of dilation, 5–13%). the narrowing may be described as "rat's tail" or "string sign". cerebral angiography is an invasive procedure, and it requires large volumes of radiocontrast that can cause complications such as kidney damage. angiography also does not directly demonstrate the blood in the vessel wall, as opposed to more modern modalities. the only remaining use of angiography is when endovascular treatment is contemplated (see below). more modern methods involve computed tomography (ct angiography) and magnetic resonance imaging (mr angiography). they use smaller amounts of contrast and are not invasive. ct angiography and mr angiography are more or less equivalent when used to diagnose or exclude vertebral artery dissection. cta has the advantage of showing certain abnormalities earlier, tends to be available outside office hours, and can be performed rapidly. when mr angiography is used, the best results are achieved in the t1 setting using a protocol known as "fat suppression". doppler ultrasound is less useful as it provides little information about the part of the artery close to the skull base and in the vertebral foramina, and any abnormality detected on ultrasound would still require confirmation with ct or mri. treatment treatment is focused on reducing stroke episodes and damage from a distending artery. four treatment modalities have been reported in the treatment of vertebral artery dissection. the two main treatments involve medication: anticoagulation (using heparin and warfarin) and antiplatelet drugs (usually aspirin). more rarely, thrombolysis (medication that dissolves blood clots) may be administered, and occasionally obstruction may be treated with angioplasty and stenting. no randomized controlled trials have been performed to compare the different treatment modalities. surgery is only used in exceptional cases. anticoagulation and aspirin aspirin (tablets pictured) is commonly used after stroke. in vertebral artery dissection it appears as effective as anticoagulation with warfarin. from analysis of the existing small treatment trials of cervical artery dissection (carotid and vertebral) it appears that aspirin and anticoagulation (heparin followed by warfarin) are equally effective in reducing the risk of further stroke or death. anticoagulation is regarded as more powerful than antiplatelet therapy, but anticoagulants may increase the size of the hematoma and worsen obstruction of the affected artery. anticoagulation may be relatively unsafe if a large stroke has already occurred, as hemorrhagic transformation is relatively common, and if the dissection extends into v4 (carrying a risk of subarachnoid hemorrhage). anticoagulation may be appropriate if there is rapid blood flow (through a severely narrowed vessel) on transcranial doppler despite the use of aspirin, if there is a completely occluded vessel, if there are recurrent stroke-like episodes, or if free-floating blood clot is visible on scans. warfarin is typically continued for 3–6 months, as during this time the flow through the artery usually improves, and most strokes happen within the first 6 months after the development of the dissection. some regard 3 months as sufficient. professional guidelines in the uk recommend that patients with va dissection should be enrolled in a clinical trial comparing aspirin and anticoagulation if possible. american guidelines state that the benefit of anticoagulation is not currently established. thrombolysis, stenting and surgery thrombolysis, stenting and surgery are not used as widely as anticoagulation or antiplatelet drugs. these treatments are invasive, and are typically reserved for situations where symptoms worsen despite medical treatment, or where medical treatment may be unsafe (e.g. an unacceptable bleeding tendency). thrombolysis is enzymatic destruction of blood clots. this is achieved by the administration of a drug (such as urokinase or alteplase) that activates plasmin, an enzyme that occurs naturally in the body and digests clots when activated. thrombolysis is an accepted treatment for heart attacks and stroke unrelated to dissection. in cervical artery dissection, only small case series are available. the thrombolytic drug is administered either intravenously or during cerebral angiography through a catheter directly into the affected artery. the data indicates that thrombolysis is safe, but its place in the treatment of vad is uncertain. stenting involves the catheterization of the affected artery during angiography, and the insertion of a mesh-like tube; this is known as "endovascular therapy" (inside the blood vessel). this may be performed to allow the blood to flow through a severely narrowed vessel, or to seal off an aneurysm. however, it is unclear whether the technical success of the procedure translates into improved outcomes, as in both cases the problem often resolves spontaneously over time. stenting, as well as the insertion of coils by means of angiography, may be performed if there is an aneurysm and/or extension of the dissection into the v4 section of the artery. surgery carries a high risk of complications, and is typically only offered in case of inexorable deterioration or contraindications to any of the other treatments. various arterial repair procedures have been described. prognosis prognosis of spontaneous cervical arterial dissection involves neurological and arterial results. the overall functional prognosis of individuals with stroke due to cervical artery dissection does not appear to vary from that of young people with stroke due to other causes. the rate of survival with good outcome (a modified rankin score of 0–2) is generally about 75%, or possibly slightly better (85.7%) if antiplatelet drugs are used. in studies of anticoagulants and aspirin, the combined mortality with either treatment is 1.8–2.1%. after the initial episode, 2% may experience a further episode within the first month. after this, there is a 1% annual risk of recurrence. those with high blood pressure and dissections in multiple arteries may have a higher risk of recurrence. further episodes of cervical artery dissection are more common in those who are younger, have a family history of cervical artery dissection, or have a diagnosis of ehlers-danlos syndrome or fibromuscular dysplasia. epidemiology the annual incidence is about 1.1 per 100,000 annually in population studies from the united states and france. from 1994 to 2003, the incidence increased threefold; this has been attributed to the more widespread use of modern imaging modalities rather than a true increase. similarly, those living in urban areas are more likely to receive appropriate investigations, accounting for increased rates of diagnosis in those dwelling in cities. it is suspected that a proportion of cases in people with mild symptoms remains undiagnosed. there is controversy as to whether vad is more common in men or in women; an aggregate of all studies shows that it is slightly higher incidence in men (56% versus 44%). men are on average 37–44 years old at diagnosis, and women 34–44. while dissection of the carotid and vertebral arteries accounts for only 2% of strokes (which are usually caused by high blood pressure and other risk factors, and tend to occur in the elderly), they cause 10–25% of strokes in young and middle-aged people. dissecting aneurysms of the vertebral artery constitute 4% of all cerebral aneurysms, and are hence a relatively rare but important cause of subarachnoid hemorrhage. history spontaneous vertebral artery dissection was described in the 1970s. prior to this, there had been isolated case reports about carotid dissection. in 1971, c. miller fisher, a canadian neurologist and stroke physician working at massachusetts general hospital, first noted the "string sign" abnormality in carotid arteries on cerebral angiograms of stroke patients, and subsequently discovered that the same abnormality could occur in the vertebral arteries. he reported the discovery in a paper in 1978. notable cases australian cricketer phillip hughes died on 27 november 2014 after developing a vertebral artery dissection as a result of being struck on the side of the neck by a cricket ball, while representing south australia in a sheffield shield match on 25 november 2014 at the s.c.g.. the short-pitched delivery bowled by n.s.w. player sean abbott struck hughes on the base of the skull, just behind his left ear which caused a vertebral artery dissection complicated by subarachnoid hemorrhage.