Have you ever seen a convexity subdural hematoma (SDH) from a high-grade (Cognard 3) dural arteriovenous fistula (dAVF)?

Dural Arteriovenous Fistulas (dAVFs) Can Cause Convexity Subdural Hematomas

Yes, high-grade dAVFs (Cognard type 3) can cause convexity subdural hematomas, and this is likely the etiology of your patient's recurrent subdural hematoma. The association between dAVFs and subdural hematomas is well-documented, particularly with high-grade lesions that have cortical venous drainage.

Pathophysiology and Risk Assessment

The Cognard type 3 dAVF you identified has several concerning features:

• Cortical venous drainage
• Parietal MMA supply
• Draining into the left transverse/sigmoid junction

These features are consistent with a high-risk lesion. According to the American Heart Association guidelines, dAVFs with cortical venous drainage have:

• 6-32.9% risk of rebleeding in the first year after initial hemorrhage 1
• 10-30% mortality rate from first hemorrhage 1
• 10-20% long-term disability among survivors 1

Relationship Between dAVF and Subdural Hematoma

The mechanism for subdural hematoma formation in dAVFs involves:

1. Increased venous pressure in cortical draining veins
2. Rupture of fragile venous structures into the subdural space
3. Progressive enlargement of hematoma due to continued abnormal flow dynamics

Your case shows a classic pattern:

• Initial subdural hematoma formation
• Surgical evacuation
• Rapid recurrence despite adequate surgical treatment
• Angiographic confirmation of dAVF

This pattern has been reported in the literature, with one case describing "non-traumatic progression to SDH" from a dAVF 2. Another study found incidental dAVFs in 10% of patients undergoing middle meningeal artery embolization for chronic subdural hematomas 3.

Management Approach

The definitive treatment for your patient should target the dAVF:

1. Endovascular embolization is the first-line approach:

   • Transarterial embolization of the feeding MMA branch
   • Complete obliteration of the fistula is essential
   • This approach has shown high success rates with acceptable morbidity 4

2. Surgical options if endovascular treatment fails:

   • Microsurgical disconnection of cortical draining veins
   • Complete surgical excision of the fistula
   • Angiographic obliteration rates of 96% have been reported 4

3. Post-treatment monitoring:

   • Regular follow-up imaging to confirm complete obliteration
   • Monitoring for recurrence of subdural collections
   • Assessment for any neurological deficits

Pitfalls and Considerations

• Incomplete treatment: Partial embolization without complete obliteration may lead to recurrent hemorrhage
• Delayed diagnosis: Failure to identify dAVF as the cause of recurrent subdural hematoma can lead to repeated unsuccessful surgeries
• Venous outflow assessment: The left brain and cerebellum using the left transverse/sigmoid sinus indicates potential venous congestion if the sinus is compromised during treatment
• Roller coaster history: The temporal relationship between the roller coaster ride and symptom onset suggests a traumatic component that may have triggered or exacerbated the dAVF

Conclusion

Your patient's recurrent subdural hematoma is most likely caused by the Cognard type 3 dAVF. Complete obliteration of the fistula through endovascular embolization is the recommended treatment to prevent further hemorrhage and neurological deterioration 5, 1.