2/Dural sinuses sit inside dural leaflets.
Arteries that feed the dura also feed the walls of sinuses, like vasa vasorum.
Arteries in the walls of veins are a natural connection between the veins and arteries—but these connections are usually closed in normal pts. x.com
Arteries that feed the dura also feed the walls of sinuses, like vasa vasorum.
Arteries in the walls of veins are a natural connection between the veins and arteries—but these connections are usually closed in normal pts. x.com
3/Whether these connections are open depends on pressure.
Like a hose w/a hole in it, at normal pressures, abnormal connections are not open.
But if pressure is increased w/thrombosis or stenosis, the connections open, like high pressure water squirting out through a hole. x.com
Like a hose w/a hole in it, at normal pressures, abnormal connections are not open.
But if pressure is increased w/thrombosis or stenosis, the connections open, like high pressure water squirting out through a hole. x.com
4/Normally venous pressure is not enough to open these connections.
However, if venous pressure is increased, usually from thrombosis, that is enough to push open these normal arteriovenous fistulas in the wall of the dural venous sinus. x.com
However, if venous pressure is increased, usually from thrombosis, that is enough to push open these normal arteriovenous fistulas in the wall of the dural venous sinus. x.com
5/Many tiny connections exist & increased pressure opens one or more.
This is why treating dAVF requires treating the fistula. If you only take out 1 artery, other connections will open & find more feeders.
Now if fistula flow goes w/sinus flow, effect is relatively benign. x.com
This is why treating dAVF requires treating the fistula. If you only take out 1 artery, other connections will open & find more feeders.
Now if fistula flow goes w/sinus flow, effect is relatively benign. x.com
6/Think of it like flow through a sink.
If dAVF flow goes w/sinus flow, it is like turning up water flow on a faucet. While it might be a waste of water, as long as the sink can handle the water, then you can manage.
Dural venous sinuses are big & can handle extra flow. x.com
If dAVF flow goes w/sinus flow, it is like turning up water flow on a faucet. While it might be a waste of water, as long as the sink can handle the water, then you can manage.
Dural venous sinuses are big & can handle extra flow. x.com
7/If you keep increasing pressure, usually from thrombosis, then pressure to flow forward becomes too much & flow goes retrograde.
It’s like a traffic jam—if the traffics too much & no one is moving, people start turning around & going the other direction. x.com
It’s like a traffic jam—if the traffics too much & no one is moving, people start turning around & going the other direction. x.com
8/Now if retrograde flow remains in the sinus, the effect is relatively benign.
Sinuses are big & used to handling lots of pressure.
Adding a bit more weight when you’re strong & able to handle big flow doesn’t result in danger. x.com
Sinuses are big & used to handling lots of pressure.
Adding a bit more weight when you’re strong & able to handle big flow doesn’t result in danger. x.com
9/The problem comes when the retrograde flow doesn’t just flow backwards in the sinus, but iis pushed backwards into the cortical veins that usually empty into the sinus.
This is called cortical venous reflux. x.com
This is called cortical venous reflux. x.com
10/Unlike dural sinuses, cortical veins are not equipped to handle this flow.
It’s like you put the weight of the earth on a puny human instead of Atlas. Flow is too much for cortical veins to handle and they are more likely to bleed. x.com
It’s like you put the weight of the earth on a puny human instead of Atlas. Flow is too much for cortical veins to handle and they are more likely to bleed. x.com
11/When the cortical veins of a dAVF become dilated, it’s a sign that the flow is too much for them & they are trying to remodel to accommodate.
This is a sign that they are failing & increases the risk that they’ll bleed. x.com
This is a sign that they are failing & increases the risk that they’ll bleed. x.com
12/If fistula flow goes retrograde into the spinal veins, these are clearly not ready for high flow from a brain AVF & are quickly overwhelmed.
If pressure is high in veins draining the cord, the cord can’t drain & you get venous HTN like a regular spinal AVF. x.com
If pressure is high in veins draining the cord, the cord can’t drain & you get venous HTN like a regular spinal AVF. x.com
13/Cortical reflux is the dividing line whether a fistula will have benign course or is likely to bleed—bc cortical veins can’t handle flow like dural sinuses & are thus more likely to bleed. x.com
14/Cognard classification defines dAVFs by the type of venous drainage—and it progresses just how I described.
If flow can go forward, it can--if not, it goes retrograde & risk of bleeding goes up by how badly the retrograde flow affects cortical veins. x.com
If flow can go forward, it can--if not, it goes retrograde & risk of bleeding goes up by how badly the retrograde flow affects cortical veins. x.com
15/But instead of memorizing the classification, ask yourself—can the venous outflow handle the flow (dural sinus vs cortical vein) & does it look like it is overwhelmed (venous ectasia)?
This will intuitively lead you to the classification system w/o having to memorize a thing! x.com
This will intuitively lead you to the classification system w/o having to memorize a thing! x.com
16/But this classification just addresses the risk of bleeding.
Itskeson et al. found 1/2 of dAVF pts had cognitive impairment. While more common w/cortical reflux, even pts w/o reflux had cognitive impairment that improved w/treatment x.com
Itskeson et al. found 1/2 of dAVF pts had cognitive impairment. While more common w/cortical reflux, even pts w/o reflux had cognitive impairment that improved w/treatment x.com
17/This begs the question if there is any truly “benign” dAVF
Even w/o high risk of bleeding, this indicates dAVFs cause more damage than we know & cognitive impairment
Should we be treating these more aggressively? x.com
Even w/o high risk of bleeding, this indicates dAVFs cause more damage than we know & cognitive impairment
Should we be treating these more aggressively? x.com
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