@erc_munich: What Causes an Arteriovenous Malformation? Arteriovenous malformations (AVMs) are congenital, meaning they develop by birth and are not caused by any disease. AVMs result from a developmental anomaly of the blood vessels in the brain, creating a tangled cluster known as a nidus. Often, AVMs remain undetected until a significant event occurs, such as a bleed, which can lead to headache and/or new neurological symptoms.. #arteriovenousmalformation #avm #braintumor #tumor #cancertreatment #radiosurgery #medicine #cancer #cyberknife #ercm