What is the annual bleed risk and risk of rebleeding for type 3 Cognard (dural arteriovenous fistulas) dAVFs, and what are the associated morbidity and mortality rates with a bleed?

Bleeding Risk and Outcomes for Type 3 Cognard dAVFs

Type 3 Cognard dural arteriovenous fistulas (dAVFs) have an annual hemorrhage risk of approximately 7.4-7.6% for symptomatic cases with cortical venous drainage, with mortality rates of 10-30% from the first hemorrhage and 10-20% of survivors experiencing long-term disability.

Annual Hemorrhage Risk

• For Type 3 Cognard dAVFs specifically:

  • Symptomatic dAVFs with cortical venous drainage (CVD): 7.4-7.6% annual hemorrhage risk 1
  • Asymptomatic dAVFs with CVD: 1.4-1.5% annual hemorrhage risk 1

• General hemorrhage risk factors for dAVFs:

  • Prior hemorrhage (strong predictor of future bleeding) 2
  • Deep venous drainage 2
  • Small AVM size 2
  • Deep or periventricular location 3
  • Presence of intranidal aneurysms 2

Risk of Rebleeding

• First year after initial hemorrhage: 6-32.9% risk of rebleeding 3
• After the first year: Risk decreases to approximately 11.3% in subsequent years 3
• After second hemorrhage: Risk increases to approximately 25% in the first year 3

Morbidity and Mortality with Hemorrhage

• Mortality from first hemorrhage: 10-30% 3, 2
• Long-term disability among survivors: 10-20% 3, 2
• Clinical outcomes:
  • In a recent study of high-grade dAVFs (including Type 3), 93% of patients had stable or improved modified Rankin Scale scores after treatment 4
  • Procedure-related permanent morbidity: 3.6% 4

Treatment Considerations

• Complete obliteration is the goal to eliminate hemorrhage risk:
  • Endovascular embolization shows high success rates (92-93.5% complete occlusion) 4, 5
  • Multimodal treatment may be necessary for complex cases 6, 7
  • Surgical disconnection is an option when endovascular approaches are limited 7

Risk Assessment Algorithm

1. Determine if the dAVF has cortical venous drainage (CVD)
2. Assess if the patient is symptomatic (hemorrhage or neurological deficits) or asymptomatic
3. Evaluate for additional risk factors:
   • Prior hemorrhage
   • Deep venous drainage
   • Presence of aneurysms
   • Location (deep/periventricular)
4. Calculate lifetime hemorrhage risk: 105 - (patient's age in years) 2

Clinical Pitfalls and Caveats

• Incomplete risk assessment that fails to consider all patient and dAVF characteristics should be avoided 2
• Partial embolization without a definitive treatment plan may not adequately reduce hemorrhage risk 2
• Regular follow-up imaging is essential to confirm complete obliteration and monitor for recurrence 2
• Late recurrences can occur even after apparent complete obliteration, warranting long-term surveillance 6
• Treatment decisions must carefully balance the natural history risk against intervention risks 2

The high mortality and morbidity associated with hemorrhage from Type 3 Cognard dAVFs, coupled with the significant annual bleeding risk, strongly supports prompt and definitive treatment in most cases, particularly for symptomatic lesions with cortical venous drainage.