Given the nonspecific clinical findings, radiologist are often the first physicians who can suggest the diagnosis, which relies on MRI.
Imaging features:
Findings on MRI are clearly explained by the physiopathology of venous hypertension, and are divided into direct visualization of tortuous intradural extramedullary vessels, and changes in the spinal cord ( Fig. 8 ).
Fig. 8: Radiologic findings are based on visualization of enlarged vessels and spinal cord edema.
Enlarged intradural channels are the most sensitive finding, manifesting as tortuous flow voids that enhance after contrast administration, mostly located at the dorsal surface of the cord in the lower thoracic region, usually spanning more than three segments. When they enlarge a scalloped appearance of the surface of the cord can appear. If significant cord swelling is present, it can compress the vascular flow voids becoming undetectable ( Fig. 9 ).
Fig. 9: Schematic representation of imaging features. The most sensitive finding is T2 hyperintensity within the cord representing edema. Lack of T2 hyperintensity in the cord in the presence of a fistula is rare, although has been reported.
Changes in the spinal cord are secondary to edema. They are multilevel (usually 5-7 vertebrae levels), affecting mostly the lower thoracic region and conus medularis (up to 90%), the latter explaining orthostasis. The segment of the cord affected does not correlate with the level of the fistula.
There is cord swelling, as well as central T1 hypointensity and central T2 hyperintensity within the cord. The length of T2 signal does not correlate with weakness or sensory/sphincter dysfunction. Lack of T2 hyperintensity in the cord in the presence of a fistula is rare, although has been reported.
There is T2 hypointensity in the periphery of the cord, probably due to pial capillaries containing deoxyhemoglobin.
After contrast administration patchy medullary enhancement can be seen due to breakdown of the blood-brain barrier ( Fig. 10 , Fig. 11 , Fig. 12 , Fig. 13 , Fig. 14 , Fig. 15 ) .
Fig. 10
Fig. 10: Characteristic MR findings of DAFV.
Fig. 11
Fig. 11: Characteristic MR findings of DAFV.
Fig. 12
Fig. 12: Characteristic MR findings of DAFV II.
Fig. 13
Fig. 13: Characteristic MR findings of DAFV III
Fig. 14
Fig. 14: Incidental dorsal DAFV found on enhanced CT
Fig. 15
Fig. 15: Clinically suspected DAVF not proven on angiography. Note some tricky pulsation artifacts dorsally to the cord. Final diagnosis of transverse myelitis secondary to lupus-like syndrome.
Optimal diagnostic approach ( Fig. 16 ):
Total spine MRI previous and after contrast administration is the initial study of choice. If this study is unconvincing, myelographic sequences (heavily T2-weigthed, like CISS or FIESTA) are very helpful to depict the extramedullary flow voids that might be obscured by pulsation artifacts. In contrast, T2 cord hyperintensity is best seen on TSE T2WI.
After identifying the presence of a dural AVF, MRI angiography should be performed in order to locate the fistula site to guide selective conventional angiography and intervention.
If MRI is contraindicated, CT angiography or CT myelography can help stablish the diagnosis (Fig. 16, Fig. 17 ).
Fig. 16
Fig. 16: Optimal diagnostic approach algorithm. Initial diagnosis is based on MRI but must be completed with MR angiography in order to guide conventional angiography.
Fig. 17
Fig. 17: Optimal diagnostic approach algorithm II.
Treatment and prognosis:
Since at the time of diagnosis most patients present with some degree of irreversible neurological disorders, the main goal of treatment is to stop progression of the disease, and somewhat improve the current disability.
The aim of treatment is to disconnect the shunting zone by embolization or surgical resection ( Fig. 18 ).
Endovascular occlusion:
Performed either with glue or Onyx after superselective catheterization of the radicular artery that supplies the fistula. The goal is deposit embolic material entering and crossing the fistula occluding the draining vein as it exits the fistula. This treatment is contraindicated if the artery also supplies the anterior spinal artery due to high risk of dissection and medullary ischemia.
Occlusion rates account for 85% but recanalization or development of new arterial feeders can occur.
Surgery:
This procedure is more aggressive but occlusion rates account for 98%. Targeted laminectomy is performed followed by disconnection of the draining vein.
Symptoms that respond well to treatment are motor and sensory disturbances.
Pain, impotence and sphincter dysfunction are reversed only in a minority of cases.
Fig. 18
Fig. 18: Treatment and Prognosis.
Posttreatment imaging ( Fig. 19 :
In patients with successfully occluded fistula, postprocedure expected changes are diminished cord enlargement, decrease in intramedullary hyperintensity and enhancement, as well as decrease in size and extent of perimedullary serpiginous venous structures.
Persistent intramedullary T2 hyperintensity and enhancement can last for up to 1 year.
If persistent perimedullary vessels are seen or the patient is clinically deteriorating, we must rule out recanalization of the arterial feeder or development of new feeders.
Fig. 19: Treatment and Prognosis II.