"type I: dural AVF"
"type II: intradural intramedullary glomus AVM"
"type III: intradural intramedullary juvenile AVM"
"type IV: perimedullary AVF"
"IVa: single feeder and small AVF"
"IVb: multiple feeders and medium AVF"
"IVc: multiple feeders and a giant AVF"
"type V: extradural AVF"