Blood vessel entanglement is called  AVM or arteriovenous malformation  ; which connects different vessels in the brain. Red blood vessels of the brain are always responsible for transporting oxygen-rich blood from the heart to the brain. Then the blood is returned to the heart and lungs through the vein. AVM interferes with this process and blood  enters the vein directly from the artery  . AVM is most often seen in the brain and in the spine.