Extradural AVF should not be confused with the more common and potentially more symptomatic dural AVF that is located inside the dura and can be associated with cord ischemia and hemorrhage.  These rare extradural lesions may be an incidental finding but can be symptomatic by way of mass effect of the distened veins on the foraminal nerve roots or spinal cord.  There are 2 types; 1 having an intradural component and 2 being entirely extradural (A producing mass effect on the cord and B showing no mass effect).