Purpose Spinal Dural Arteriovenous Fistula (SDAVF) is a rare acquired lesion that can impair spinal cord function. Early diagnosis is very important since the symptoms can be reversed if treated prior to irreversible cord ischemia or infarction. Characteristic features of the spinal MRI includes multi-leveled T2 hyperintensity in the spinal cord signifying cord edema and prominent flow voids in the extramedullary and intradural space from venous congestion. These prominent flow voids are commonly mistaken for primary vascular malformation. It is important to note that the flow voids are the consequence of venous congestion and not the site of fistulous shunting. The understanding of this disease process is pertinent in safe treatment planning. We aim to show that neither the distribution of flow voids nor the intramedullary findings are related to the location of the fistula.

Materials and Methods We retrospectively analyzed cases of SDAVFs in the last 2 years. All patients underwent clinical examination, MRI of the whole spine and spinal digital subtraction angiogram (DSA). We compared the level of the fistula based on the clinical presentation and MR images with that of the DSA findings.

Results There were a total of 7 cases of SDAVFs. All patients presented with progressive myelopathy. Initial MRI showed extensive T2 hyperintensity in the spinal cord and flow voids in the extramedullary, intradural space. Subsequent DSA identified the location of the fistula ranging from the cranio-cervical junction to the sacral level. Clinical presentation and MRI findings were not predictive of location of fistula found on spinal DSA. In one case, the patient's time resolved MR angiography was able to localize the fistula which was later confirmed on spinal DSA.

Discussion SDAVFs represent an abnormal connection between the segmental dural arterial supply and the vein, which eventually drain into the perimedullary vein. This results in retrograde venous congestion in the spinal cord. This usually manifest as dilated perimedullary veins on MRI and T2 hyperintensity in spinal cord secondary to congestion and edema and clinically as progressive myelopathy. Since the spinal perimedullary venous system is an integrated system, congestion secondary to SDAVF at any spinal level can result in venous congestion of the spinal cord. Hence, the venous congestion is the consequence and not the cause and result in the characteristic clinical and MRI presentations. Only spinal DSA accurately demonstrate the fistula location. Standard contrast-enhanced MR angiography in combination with MRI has been shown recently to increase accuracy of fistula localization.

Summary Clinical presentation and MRI findings are very useful in pointing toward the diagnosis of SDAVF but do not give any indication about of the location of fistula. Location of fistula can be shown only on spinal DSA or in some cases time resolved MR angiography. This understanding is very important in the planning of safe treatment.