  arteriovenous malformation (avm) is an abnormal connection between arteries and veins, bypassing the capillary system. this vascular anomaly is widely known because of its occurrence in the central nervous system, but can appear in any location. although many avms are asymptomatic, they can cause intense pain or bleeding or lead to other serious medical problems. avms are usually congenital and belong to the rasopathies. the genetic transmission patterns of avm, if any, are unknown. avm is not generally thought to be an inherited disorder, unless in the context of a specific hereditary syndrome. == signs and symptoms == symptoms of avm vary according to the location of the malformation. roughly 88%national institute of neurological disorders and stroke of people affected with avm are asymptomatic; often the malformation is discovered as part of an autopsy or during treatment of an unrelated disorder (called in medicine "an incidental finding"); in rare cases its expansion or a micro-bleed from an avm in the brain can cause epilepsy, deficit or pain. the most general symptoms of a cerebral avm include headache and epilepsy, with more specific symptoms occurring that normally depend on the location of the malformation and the individual. such possible symptoms include: * difficulties with movement coordination, including muscle weakness and even paralysis; * vertigo (dizziness); * difficulties of speech (dysarthria) and communication, such as aphasia; * difficulties with everyday activities, such as apraxia; * abnormal sensations (numbness, tingling, or spontaneous pain); * memory and thought-related problems, such as confusion, dementia or hallucinations. cerebral avms may present in a number of ways *hemorrhage (45% of cases) **acute onset of severe headache. may be described as the worst headache of the patient's life. depending on the location of hemorrhage, may be associated with new fixed neurologic deficit. in unruptured brain avms, the risk of spontaneous hemorrhage may be as low as 1% per year. after a first rupture, the annual bleeding risk may increase to more than 5%.{{cite journal |author=stapf c, mast h, sciacca rr, et al. |title=predictors of hemorrhage in p
Congenital_vascular_defects Gross_pathology RASopathies