Spinal epidural arteriovenous fistulas with perimedullary venous drainage cause venous hypertension, and usually manifest as slowly progressive myelopathy. We treated two patients presenting with sudden onset of severe neurological deficits. Moreover, in Case 1, the venous drainage was exclusively epidural and no perimedullary venous drainage was present. Angiographic findings of this patient were characterized by a slow-flow fistula with marked retention of the epidural venous drainage. Rapidly progressing thrombosis of the epidural venous plexus may have caused the sudden onset of the symptoms. In Case 2, hematomyelia may also be possibly associated with the sudden onset of the symptoms. Early diagnosis and treatment are essential to achieve favorable outcome in such cases because venous congestion results in irreversible venous infarction within a short period.