Neuroradiology · Neurovascular malformations · 1.0
Borden classification of dural arteriovenous fistulas
A three-tier classification of cranial and spinal dural arteriovenous fistulas based on the site of venous drainage and the presence of cortical venous reflux.
Purpose
To stratify cranial and spinal dural arteriovenous fistulas by venous drainage pattern, separating lesions that drain anterogradely into a dural sinus or meningeal vein from those with retrograde or exclusive cortical (subarachnoid) venous drainage, which carry an aggressive natural history.
| Type | Venous drainage | Cortical venous reflux | Implication |
|---|---|---|---|
| I | Drains anterogradely into a dural venous sinus or meningeal vein | Absent | Benign course; treat for symptoms such as bruit, orbital congestion or intolerable tinnitus rather than for rupture risk |
| II | Drains into a dural venous sinus with retrograde flow into subarachnoid (cortical) veins | Present | Aggressive course; treatment generally indicated, aiming to eliminate the cortical venous reflux |
| III | Drains directly and exclusively into subarachnoid (cortical) veins, with no sinus drainage | Present (sole drainage route) | Aggressive course; treatment generally indicated, with disconnection of the draining vein at the fistulous point |
| Subtype a / b | Applied to any type: a = single fistulous connection; b = multiple fistulous connections | Determined by the type, not by the subtype | Subtype b lesions are more difficult to cure and more likely to need staged or combined treatment |
How to use it
- The classifying variable is the venous side, not the arterial supply; the number, size or origin of feeding dural arteries does not change the Borden type.
- Cortical venous drainage is the single feature that separates benign (type I) from aggressive (types II and III) lesions, because subarachnoid venous hypertension underlies haemorrhage and non-haemorrhagic neurological deficit.
- Type II and type III lesions differ only in whether a dural sinus is still involved in the drainage; both carry cortical venous reflux and both are treated with the aim of abolishing that reflux.
- Borden compresses the more granular Cognard scheme: Cognard I and IIa map to Borden I, Cognard IIb and IIa+b to Borden II, and Cognard III, IV and V to Borden III.
- The system applies to spinal as well as cranial dural fistulas; a spinal dural arteriovenous fistula draining into a perimedullary vein is, by definition, a type III lesion.
Common mistake
Assigning the type from the arterial supply or from the angiographic 'shunt volume' instead of from the venous drainage pattern, and treating an occluded or thrombosed sinus as an incidental finding — sinus outflow occlusion can convert an earlier type I fistula into a type II or III lesion with cortical venous reflux on follow-up angiography.
Exam pearl
Borden types on venous drainage only: I = sinus or meningeal vein, antegrade; II = sinus plus cortical reflux; III = cortical veins alone. Cortical venous drainage equals aggressive behaviour; subtype a is a single fistula, b multiple.
Viva questions
- On what single variable is the Borden classification of dural arteriovenous fistulas based?
- On the site of venous drainage — whether the shunt drains into a dural venous sinus or meningeal vein, or into subarachnoid cortical veins — and not on the arterial supply.
- Define the three Borden types.
- Type I drains antegradely into a dural venous sinus or meningeal vein without cortical reflux. Type II drains into a dural sinus with retrograde reflux into cortical veins. Type III drains directly and only into subarachnoid cortical veins.
- What do the subtypes a and b denote?
- Subtype a indicates a single fistulous connection and subtype b multiple fistulous connections; the subtype can be applied to any of the three types and predicts difficulty of cure rather than natural history.
- Why does cortical venous drainage matter?
- Arterialised flow into thin-walled subarachnoid veins produces venous hypertension, which is the mechanism of intracranial haemorrhage and of non-haemorrhagic neurological deficit; its presence defines the aggressive types II and III.
- How does Borden map onto the Cognard classification?
- Cognard I and IIa correspond to Borden I, Cognard IIb and combined IIa+b to Borden II, and Cognard III, IV and V to Borden III.
- How does the Borden type alter management?
- Type I lesions are managed conservatively or treated only for disabling symptoms, whereas types II and III are generally treated, with the endpoint being elimination of cortical venous reflux — typically by disconnecting the draining vein at the fistulous point.
- Can a type I fistula change category over time?
- Yes — progressive stenosis or thrombosis of the draining dural sinus can redirect flow into cortical veins, converting a benign type I lesion into a type II or III lesion, so new symptoms warrant repeat angiography.
- What Borden type is a classic spinal dural arteriovenous fistula?
- Type III, because the shunt drains directly into a perimedullary (subarachnoid) vein with no dural sinus involvement.