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Thursday, May 14, 2009

Dural arteriovenous fistula

(Figure 1 shows a cranial DAVF as seen on a side-on or lateral view of a cerebral angiogram. The small fistulae are in the dura (red circles). The arterial supply is marked by the red arrows (branches of the external and internal carotid arteries). In this case, there is no distinct draining vein, but there is a thrombosed dural venous sinus in the vicinity of the fistulae. The blocked or thrombosed portion of the sinus is shown by dark-blue arrow heads, the normal open portion is shown by light-blue arrow heads.)


A dural arteriovenous fistula, also called a dural arteriovenous malformation, is an abnormal direct connection (fistula) between a meningeal artery and a meningeal vein or dural venous sinus.

( Unruptured intracranial dural arteriovenous fistula.)


Classification

The Borden Classification of Dural arteriovenous malformations or fistulas, groups into three types based upon their venous drainage:

  1. Type I: dural arterial supply drains anterograde into venous sinus.
  2. Type II: dural arterial supply drains into venous sinus. High pressure in sinus results in both anterograde drainage and retrograde drainage via subarachnoid veins.
  3. Type III: dural arterial supply drains retrograde into subarachnoid veins.

Type I

Type I dural arteriovenous fistulas are suppied by meningeal arteries and drain into a meningeal vein or dural venous sinus. The flow within the draining vein or venous sinus is anterograde.

  1. Type Ia -- simple dural arteriovenous fistulas have a single meningeal arterial supply
  2. Type Ib -- more complex arteriovenous fistulas are supplied my multiple meningeal arteries

The distinction between Types Ia and Ib is somewhat specious as there is a rich system of meningeal arterial collaterals. Type I dural fistulas are often asymptomatic, do not have a high risk of bleeding and do not necessarily need to be treated.

Type II

The high pressure within a Type II dural AV fistula causes blood to flow in a retrograde fashion into subarachnoid veins which normally drain into the sinus. Typically this is because the sinus has outflow obstruction. Such draining veins form venous varices or aneuryms which can bleed. Type II fistulas need to be treated to prevent hemorrhage. The treatment may involve embolization of the draining sinus as well as clipping or embolization of the draining veins.

Type III

Type III dural AV fistulas drain directly into subarachnoid veins. These veins can form aneurysms and bleed. Type III dural fistulas need to be treated to prevent hemorrhage. Treatment can be as simple as clipping the draining vein at the site of the dural sinus. If treatment involves embolization, it will only typically be effective if the glue traverses the actual fistula and enters, at least slightly, the draining vein.


Treatment

One approach used for treatment is embolization.



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