Cerebral arteriovenous malformation

The most frequently observed problems related to a cerebral arteriovenous malformation (AVM) are headaches and seizures, cranial nerve afflictions including pinched nerve and palsy, Symptoms due to bleeding include loss of consciousness, sudden and severe headache, nausea, vomiting, incontinence, and blurred vision, amongst others. AVMs in certain critical locations may stop the circulation of the cerebrospinal fluid, causing it to accumulate within the skull and giving rise to a clinical condition called hydrocephalus. A stiff neck can occur as the result of increased pressure within the skull and irritation of the meninges. ==Pathophysiology==

A cerebral AVM is an abnormal anastomosis (connection) between the arteries and veins in the brain due to the lack of a capillary bed, and is most commonly of prenatal origin. The overall annual incidence of haemorrhage from a ruptured AVM is 2-4%. Smaller AVMs have a greater propensity for haemorrhaging, whereas larger AVMs tend to more often cause seizures instead. ==Diagnosis==

from ventricular puncture, not to be mistaken for an aneurysmal malformation A cerebral AVM diagnosis is established by neuroimaging studies after a complete neurological and physical examination. Three main techniques are used to visualize the brain and search for an AVM: computed tomography (CT), magnetic resonance imaging (MRI), and cerebral angiography. A CT scan of the head is usually performed first when the subject is symptomatic. It can suggest the approximate site of the bleed. MRI is more sensitive than CT in the diagnosis, and provides better information about the exact location of the malformation. More detailed pictures of the tangle of blood vessels that compose an AVM can be obtained by using radioactive agents injected into the blood stream. If a CT is used in conjunction with an angiogram, this is called a computerized tomography angiogram; while, if MRI is used it is called magnetic resonance angiogram. The best images of a cerebral AVM are obtained through cerebral angiography. This procedure involves using a catheter, threaded through an artery up to the head, to deliver a contrast agent into the AVM. As the contrast agent flows through the AVM structure, a sequence of images are obtained. ==Grading==

Spetzler-Martin (SM) Grade A common method of grading cerebral AVMs is the Spetzler-Martin (SM) grade. This system was designed to assess the patient's risk of neurological deficit after open surgical resection (surgical morbidity), based on characteristics of the AVM itself. Based on this system, AVMs may be classified as grades 1–5. This system was not intended to characterize risk of hemorrhage. "Eloquent" is defined as areas within the brain that, if removed will result in loss of sensory processing or linguistic ability, minor paralysis, or paralysis. These include the basal ganglia, language cortices, sensorimotor regions, and white matter tracts. Importantly, eloquent areas are often defined differently across studies where deep cerebellar nuclei, cerebral peduncles, thalamus, hypothalamus, internal capsule, brainstem, and the visual cortex could be included. The risk of post-surgical neurological deficit (difficulty with language, motor weakness, vision loss) increases with increasing Spetzler-Martin grade. Supplemented Spetzler-Martin (SM-supp, Lawton-Young) Grade A limitation of the Spetzler-Martin Grading system is that it does not include the following factors: Patient age, hemorrhage, diffuseness of nidus, and arterial supply. In 2010 a new supplemented Spetzler-Martin system (SM-supp, Lawton-Young) was devised adding these variables to the SM system. Under this new system AVMs are classified from grades 1–10. It has since been determined to have greater predictive accuracy than SM grades alone. ==Treatment==

Treatment depends on the location and size of the AVM and whether there is bleeding or not. The treatment in the case of sudden bleeding is focused on restoration of vital function. Medical Anticonvulsant medications such as phenytoin are often used to control seizure; medications or procedures may be employed to relieve intracranial pressure. Eventually, curative treatment may be required to prevent recurrent hemorrhage. However, any type of intervention may also carry a risk of creating a neurological deficit. Surgical Surgical elimination of the blood vessels involved is the preferred curative treatment for many types of AVM. Radiosurgical Radiosurgery has been widely used on small AVMs with considerable success. The Gamma Knife is an apparatus used to precisely apply a controlled radiation dosage to the volume of the brain occupied by the AVM. While this treatment does not require an incision and craniotomy (with their own inherent risks), three or more years may pass before the complete effects are known, during which time patients are at risk of bleeding. Neuroendovascular therapy Embolization is performed by interventional neuroradiologists and the occlusion of blood vessels most commonly is obtained with ethylene vinyl alcohol copolymer (Onyx) or n-butyl cyanoacrylate. These substances are introduced by a radiographically guided catheter, and block vessels responsible for blood flow into the AVM. Embolization is frequently used as an adjunct to either surgery or radiation treatment. Risks A first-of-its-kind controlled clinical trial by the National Institutes of Health and National Institute of Neurological Disorders and Stroke focuses on the risk of stroke or death in patients with an AVM who either did or did not undergo interventional eradication. Early results suggest that the invasive treatment of unruptured AVMs tends to yield worse results than the therapeutic (medical) management of symptoms. Because of the higher-than-expected experimental event rate (e.g. stroke or death), patient enrollment was halted by May 2013, while the study intended to follow participants (over a planned 5 to 10 years) to determine which approach seems to produce better long-term results. ==Prognosis==

The main risk is intracranial hemorrhage. This risk is difficult to quantify since many patients with asymptomatic AVMs will never come to medical attention. Small AVMs tend to bleed more often than do larger ones, the opposite of cerebral aneurysms. If a rupture or bleeding incident occurs, the blood may penetrate either into the brain tissue (cerebral hemorrhage) or into the subarachnoid space, which is located between the sheaths (meninges) surrounding the brain (subarachnoid hemorrhage). Bleeding may also extend into the ventricular system (intraventricular hemorrhage). Cerebral hemorrhage appears to be most common. Ruptured AVMs are a significant source of morbidity and mortality; following a rupture, as many as 29% of patients will die, with only 55% able to live independently. ==Epidemiology==

The annual new detection rate incidence of AVMs is approximately 1 per 100,000 a year. The point prevalence in adults is approximately 18 per 100,000. AVMs are more common in males than females, although in females pregnancy may start or worsen symptoms due to the increase in blood flow and volume it usually brings. There is a significant preponderance (15–20%) of AVM in patients with hereditary hemorrhagic telangiectasia (Osler–Weber–Rendu syndrome). ==References==