While suffering from AVM, the main risk is the bleeding of the skull. This is because patients with no symptoms rarely visit the specialist for checkups. Unlike cerebral aneurysms if the AM is small then the bleeding will be more. The vice versa is also true.
The bleeding can extend to the brain tissue (cerebral hemorrhage) or into the spaces of the subarachnoid. It might even go to the extent of the ventricular system.