venerdì 10 agosto 2007
Spinal dural arteriovenous fistula
Figure 1, Figure 2, and Figure 3: Sagittal T2 images of the spine demonstrate low signal tortuous vessels in the posterior epidural space.
Figure 3: Sagittal T2 image demonstrates abnormal high signal within the lower cord consistent with myelopathy. The level of myelopathy does not necessarily correlate with the level of the fistula.
Diagnosis: Spinal dural arteriovenous fistula
The term “spinal vascular malformation” is a general term that encompasses a variety of spinal vascular lesions. In 2002, Spetzler et al. proposed a revision to the prior I-IV classification system that is more descriptive and functional. Spetzler categorizes vascular lesions as neoplastic, aneurysms, and abnormal communications between arteries and veins. The last category can be further subdivided into arteriovenous malformations and arteriovenous fistulas, with even further subclassification based upon location within the spinal canal. Arteriovenous malformations can be extramedullary-intramedullary and/or intramedullary. Arteriovenous fistulas can be extradural or intradural (dorsal or ventral).
Intradural dorsal arteriovenous fistulas are the most common type of spinal AV fistula and are thought to be acquired. AVFs represent an abnormal communication between a spinal radicular artery and a medullary draining vein. Over time, the high pressure of the artery communicating with the draining vein creates a functional obstruction to venous flow, resulting in spinal venous engorgement and hypertension. Clinically, this manifests as progressive myelopathy. The typical patient with a spinal AVM or AVF is usually a male over 40 that presents with progressive lower extremity weakness and bowel and bladder difficulties.
There are several imaging findings in patients with spinal dural AVFs. Specifically, MRI demonstrates dilated spinal veins as tiny flow voids within the intradural compartment. Most dural fistulas are located in the lower thoracic and lumbar spinal levels, with associated increased T2 signal within the cord secondary to myelopathy from venous congestion. Note however that the location of the dilated veins and myelopathy does not always correlate with the level of the fistula.
The use of spinal MR angiography in evaluating patients prior to conventional catheter angiography of the spine has become a hot topic in recent years. Advantages that have been discussed include the decreased contrast load and radiation exposure because the angiographer can perform a targeted diagnostic and possibly therapeutic procedure. Even more recently, CT angiography has been employed in a similar role.
Treatment of dural fistulas is tailored to the functional anatomy of the vascular malformation. Treatment options include embolization, which can be therapeutic or pre-surgical, and surgical resection.