OBJECTIVE:To describe and present atypical spinal dural arteriovenous fistulae (SDAVFs) that drain into the anterior spinal vein (ASV) and thus cause some degree of difficulty in differentiating the anterior spinal artery from the ASV.METHODS:A retrospective review of 80 selective spinal angiography procedures (with or without endovascular treatment) performed on SDAVFs since 1980 identified three cases in which the venous drainage was into a dilated ASV via a radicular vein. The patients included two men and one woman, ranging in age from 55 to 82 years (mean age, 71 yr), all of whom presented with mild to severe progressive paraparesis and sensory disturbance.RESULTS:The appearance of the venous drainage mimicked that of the usual hairpin configuration of the radiculomedullary artery and therefore caused diagnostic difficulty. There are no characteristic clinical features that differentiate this form of SDAVF from the usual type of SDAVF. The angiographic criteria for identification of the ASV draining an SDAVF include the demonstration of the branching of the ASV and its drainage into the epidural vein, opacification of other medullary veins connected with the ASV, recognition of distortion of the hairpin shape, and the identification of the anterior spinal artery at the segment where the ASV is opacified. Two patients were treated with embolization and one with surgery. All patients improved after the treatment.CONCLUSION:Before performing endovascular treatment, thorough spinal angiography with an appropriate field of view must be performed to identify this unusual type of SDAVF.