Patients with spinal arteriovenous malformations (AVMs) may have an insidious, subacute or acute onset of symptoms, depending on the type of AVM and the mechanism of cord injury. Before recommending treatment, one must consider the expected clinical course based on knowledge of the natural history of the specific type of vascular abnormality affecting the patient and the risks and potential benefits of the proposed treatment. However, knowledge of the natural history of patients with spinal vascular abnormalities is incomplete. As with other rare disorders for which therapy is attempted, it is known only from retrospective studies. Furthermore, additional factors mitigate the usefulness of the previous studies. Most information on the natural history of spinal AVMs was acquired when they were all considered to be congenital AVMs of the spinal cord. Only in the past decade has it been generally recognized that the spinal vascular abnormalities are not a single entity, but are comprised of several biologically distinct forms. Based on origin, epidemiology, anatomy, pathophysiology, clinical presentation, and prognosis, three main types of spinal vascular abnormalities are now recognized: dural arteriovenous fistulas (AVFs), intradural vascular malformations and cavernous angiomas of the spinal cord (Table 8.1) (Oldfield & Doppman 1988; Oldfield 1991).

Since each type of vascular abnormality appears to be a biologically distinct entity (Rosenblum et al. 1987; Oldfield & Doppman 1988), the natural history and the influence of treatment of each type must be considered separately.