Arteriovenous malformation 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 (usually cerebral AVM), 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 AVMs are incomplete, but there are known genetic mutations (for instance in the epithelial line, tumor suppressor PTEN gene) which can lead to an increased occurrence throughout the body. Signs and symptoms Symptoms of AVM vary according to the location of the malformation. Roughly 88% of people with an 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, neurological deficit, or pain. The most general symptoms of a cerebral AVM include headaches and epileptic seizures, 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 themselves in a number of different ways: Bleeding (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 bleeding, may be associated with new fixed neurologic deficit. In unruptured brain AVMs, the risk of spontaneous bleeding may be as low as 1% per year. After a first rupture, the annual bleeding risk may increase to more than 5%. Seizure or brain seizure (46%) Depending on the place of the AVM, it can cause loss of vision in one place. Headache (34%) Progressive neurologic deficit (21%) May be caused by mass effect or venous dilatations. Presence and nature of the deficit depend on location of lesion and the draining veins. Pediatric patients Heart failure Macrocephaly Prominent scalp veins Pulmonary arteriovenous malformations Pulmonary arteriovenous malformations are abnormal communications between the veins and arteries of the pulmonary circulation, leading