Can Dural AV Fistula Be Detected on Non-Contrast MRA/MRV?
Yes, dural arteriovenous fistulas can be detected on non-contrast MRA/MRV, particularly using time-of-flight (TOF) techniques, though detection capability varies by fistula characteristics and imaging protocols.
Detection Capability of Non-Contrast MRA
Non-contrast 3D time-of-flight MRA demonstrates good diagnostic performance for dural AVF detection. For intracranial dural AVFs, unenhanced 3T 3D TOF MRA shows excellent intermodality agreement with DSA for identifying the fistula site (κ = 0.968) and good agreement for main arterial feeders (κ = 0.809) and venous drainage patterns (κ = 0.837) 1. This means non-contrast MRA can reliably identify the location and basic architecture of most dural AVFs.
The ACR Appropriateness Criteria note that time-of-flight MRA demonstrates excellent intermodality agreement with DSA regarding fistula site location and good agreement for arterial feeding vessels and venous drainage 2. However, the guidelines emphasize that while MRA is frequently used in surveillance, it lacks the temporal resolution for detailed hemodynamics and small vessel angioarchitecture.
Key Strengths and Limitations
What Non-Contrast MRA Can Detect:
- Fistula site location: Correctly identified in 6 of 7 cases in one series 3
- Presence and laterality: Accurately determined in all patients in multiple studies 1, 4
- Dilated cortical veins: Suggestive finding when seen without a parenchymal nidus 5
- Venous drainage patterns: Generally well-visualized
Critical Limitations:
- Small fistulas (<1 cm): Limited sensitivity 2
- Cortical venous reflux: Slightly lower negative predictive value compared to CTA 2
- High-grade features: May miss subtle cortical reflux (as seen in one grade 2b DAVF case) 4
- Arterial feeders: Less well-depicted than on DSA 3
Clinical Algorithm for Using Non-Contrast MRA/MRV
When to rely on non-contrast MRA/MRV:
- Initial screening for suspected dural AVF
- Surveillance of known low-grade lesions
- Patients with contraindications to contrast (renal dysfunction, allergies)
When non-contrast imaging is insufficient:
- High clinical suspicion despite negative non-contrast study (consider repeat with contrast or DSA)
- Treatment planning requiring detailed angioarchitecture
- Suspected high-grade fistula with cortical venous drainage
- Small or complex lesions
Important Caveats
The absence of flow voids on routine MRI does not exclude dural AVF. One case report describes a spinal dural AVF with T2 hyperintensity but no significant flow voids, initially mimicking a spinal cord tumor 6. This highlights that conventional MRI sequences may miss AVFs, making dedicated MRA/MRV essential when clinical suspicion exists.
Time-resolved (4D) techniques improve detection. Advanced non-contrast methods like Time-SLIP 3D MR digital subtraction angiography provide hemodynamic information and correctly identified presence and side of DAVF in all patients in one series, though it missed cortical reflux in one grade 2b case 4. The 4D-combo-MRV technique successfully detected both coincidental and de novo DAVFs in CVT patients 7.
Bottom Line for Clinical Practice
Non-contrast MRA/MRV serves as an effective screening tool for dural AVFs, particularly for larger lesions and initial detection. However, it cannot replace DSA for definitive diagnosis, treatment planning, or evaluation of high-grade features. When non-contrast MRA suggests a dural AVF, proceed to either contrast-enhanced MRA or DSA for complete characterization before treatment decisions. For spinal dural AVFs specifically, recent evidence suggests MRA may actually be more sensitive than DSA (100% vs 85.7%) 8, making it an excellent first-line diagnostic tool in that specific context.