Arteriovenous malformation or AVM is a congenital disorder of unknown cause, which produces diffuse or localized vascular lesions consisting of tangle(s) of vessels with abnormal connections and no capillaries. Since the normal structure of the vessels are lacking, they are extremely fragile and easy to bleed. AVMs can occur in various parts of the body including the brain (see cerebral arteriovenous malformation), spleen, lung, kidney and liver. AVMs may occur in isolation or as a part of another disease (e.g. von Hippel-Lindau disease or Rendu-Osler-Weber syndrome).