Spinal dural arteriovenous fistula (SDAVF) is also known as a type 1 spinal arteriovenous malformation, representing the most frequent vascular malformation of the spine. A high suspicion index is often required for the initial diagnosis of SDAVF because of subtle magnetic resonance imaging signs. We present the case of a patient with SDAVF associated with syringomyelia of the thoracic spinal cord and hypothesize that a fistula might induce intramedullary fluid accumulation due to venous hypertension, which leads to syrinx formation.