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Vascular & Stroke

AVM vs Dural AV Fistula: Where the Shunt Lives

Fellowship-level neuroradiology teaching by E. Brooke Schrickel, MD. Open this topic in the interactive reading room →

Watch · concise explainerHow to tell them apart

Core clinical idea

Both are arteriovenous shunts, but where the shunt lives and how it drains decide everything: a true (pial) AVM has a parenchymal nidus fed by cortical/pial arteries, while a dural AV fistula has the shunt inside the dura with NO parenchymal nidus, fed by meningeal/external-carotid branches. In both, the feature that predicts hemorrhage is cortical venous reflux — so the report stands or falls on identifying and grading the venous drainage.

Bottom line

Find the shunt and read its venous drainage — pial nidus (AVM, grade by Spetzler-Martin) vs dural shunt with no nidus (dAVF, grade by cortical venous reflux). Cortical venous drainage is the hemorrhage driver in both.

Core workstation questions

  • Is there a parenchymal nidus (AVM) or no nidus at all (dAVF)?
  • Who feeds it — pial/cortical arteries (AVM) or dural/meningeal/ECA branches (dAVF)?
  • Is there cortical venous reflux / retrograde leptomeningeal venous drainage — the single highest-risk feature?
  • For an AVM: what is the size, is it in eloquent cortex, and is venous drainage deep — the three Spetzler-Martin axes?
  • Are there flow-related, nidal, or venous (varix) aneurysms that raise rupture risk?

What changes reporting / management

  • For an AVM, give the Spetzler-Martin grade: size (<3 cm = 1, 3-6 cm = 2, >6 cm = 3) + eloquent location (+1) + deep venous drainage (+1), total out of 5 — it predicts surgical morbidity.
  • For a dAVF, the report hinges on cortical venous reflux: Borden II-III / Cognard IIb and above carry a high hemorrhage/neurologic-deficit risk and warrant treatment; name the involved sinus (transverse-sigmoid, cavernous, tentorial) and location.
  • Treat unexplained unilateral cortical venous engorgement, white-matter edema, or venous-pattern hemorrhage as a clue to an occult dAVF and recommend catheter angiography.
  • State that DSA remains the reference standard for both — for nidus architecture, feeders, and the venous drainage pattern that grading depends on.

Practical traps

  • Missing a dAVF because there is no nidus and the arterial feeders are small — the diagnosis is in the veins (engorged pial veins, venous hypertension).
  • Calling dural/ECA arterial supply a pial AVM.
  • Under-reporting cortical venous reflux — it is the feature that changes management in both lesions.
  • Confusing a benign non-shunting developmental venous anomaly or capillary telangiectasia with an arteriovenous shunt.

Teaching pearls

  • AVM = parenchymal nidus with pial feeders; dAVF = dural shunt, no nidus, meningeal/ECA feeders.
  • Cortical venous reflux is the hemorrhage driver in both — find it and grade it.
  • Spetzler-Martin (size + eloquence + deep drainage) grades AVM surgical risk; Borden/Cognard grade dAVF by venous drainage.
  • Unexplained unilateral cortical venous engorgement or edema → hunt for a dural AV fistula.
  • A developmental venous anomaly is a normal variant, not a shunt — don't put it in this differential.

Teaching visuals

AVM vs dural AV fistula — nidus in brain vs shunt in duraCoronal · for both, cortical venous reflux is what bleedsAVMnidus IN the brainartery -> nidus -> vein,no capillary beddAVFshunt IN the duraCortical venousreflux -> bleedsTELL THEM APARTwhere is the shunt?AVMnidus in brain parenchyma(pial); fed by pial arteries;grade by Spetzler-Martindural AVFshunt in the dural sinus wall;NO parenchymal nidus; fed bydural/ECA branchesWhat bleedscortical venous reflux —retrograde arterial flow intocortical veinsGrade the veinsdAVF: Borden / Cognard by venousdrainage; reflux = aggressiveThe clinical hingeAVM is a nidus sitting IN the brain; a dural AV fistula is a shunt sitting in the DURA (sinus wall) with noparenchymal nidus. Pin the shunt's location first.For both, the venous side decides danger: cortical venous reflux (arterialized flow forced backwards into corticalveins) is what raises pressure and bleeds — and it's what upgrades a dAVF to an aggressive lesion.
AVM vs Dural AV Fistula (+ Spetzler-Martin)

Source lectures

  • AVM vs Dural AV Fistula

Educational material for radiology residents and neuroradiology fellows. Nothing here drives individual patient care, and it contains no patient data.