An arteriovenous malformation is a direct connection between an artery and a vein without passing through capilliaries. Depending on the location of the malformation, it can cause a variety of symptoms but in the vast majority of cases, the malformation is completely asymptomatic. The most likely symptom is hypoxia in the area fed by the artery resulting in muscle weakness or even paralysis. They can also cause vertigo, aphasia, peripheral neuropathy and even dementia and other neurological problems.

Most malformations are congenital, but can arise from trauma and some diseases such as hereditary hemorrhagic telangiectasia and Von Hippel-Lindau Syndrome.

Arteriovenous malformations are a common diagnosis on House, M.D.

• In DNR, John Henry Giles had a malformation on his spine which caused paralysis and was mistaken for ALS.
• In Resignation, Addie's attempt to commit suicide by swallowing a caustic substance resulted in an internal injury which, when it healed, resulted in a malformation in her intestine that allowed bacteria to enter her bloodstream.
• In Top Secret, John Kelley had numerous malformations at the result of his hereditary hemorrhagic telangiectasia.

Arteriovenous malformation at Wikipedia