Brain AVM Overview

Overview

This lecture covers the imaging, classification, clinical significance, and key risk factors of brain arteriovenous malformations (AVMs), focusing on what radiologists need to know for diagnosis and reporting.

Types of Brain Vascular Malformations

• Five main types: developmental venous anomaly, capillary telangiectasia, cerebral cavernous malformation, arteriovenous malformation (AVM), and arteriovenous fistula.
• Grouped into slow-flow (venous/capillary) and high-flow (arteriovenous) malformations.
• High-flow malformations (AVM, fistula) feature direct artery-to-vein shunts and high pressure.

AVM Basics & Clinical Importance

• AVMs are congenital, sporadic lesions with a nidus (tangle of abnormal vessels).
• Most common cause of spontaneous brain hemorrhage in children and young adults under 40.
• Hemorrhage occurs in about 50% of AVM cases; seizures and incidental findings are other presentations.

Imaging and Recognition of AVMs

• Gold standard: Digital subtraction angiography (DSA), allows detailed analysis of nidus, feeding arteries, and draining veins.
• CT/CTA and MRI/MRA can also show key AVM components (nidus, hypertrophic feeding arteries, draining veins).
• AVM nidus appears as a "bag of worms"—tangle of vessels—on imaging.

AVM Risk Factors and Hemorrhage Risk

• Annual hemorrhage risk: 2–4% for unruptured AVMs, 6–15% for previously ruptured AVMs.
• Lifetime hemorrhage risk significant (up to 70% for a 40-year-old with unruptured AVM).
• Increased hemorrhage risk with: deep venous drainage, small nidus size, deep/eloquent location, associated aneurysms, and venous drainage obstruction.

Reporting & Risk Assessment

• Report AVM location (superficial, deep, eloquent brain areas), size, feeding artery type, and presence of aneurysms.
• Evaluate venous drainage pattern (deep vs. superficial) and venous stenosis/obstruction.
• Note signs of prior hemorrhage, which raises future hemorrhage risk.

Spetzler-Martin Grading Scale

• Grades AVMs by nidus size, eloquence of location, and deep vs. superficial venous drainage.
• Lower grades (1–2) indicate lower surgical risk; higher grades (4–5) suggest high surgical risk.

Key Terms & Definitions

• Nidus — Tangle of abnormal vessels in an AVM forming the shunt.
• High-flow malformation — Vascular abnormality with direct artery-to-vein shunt.
• Deep venous drainage — Blood drains from AVM into deep veins, increasing hemorrhage risk.
• Eloquent brain area — Region where minor damage causes major neurological deficits.
• Feeding artery — Artery supplying blood to the AVM nidus.
• Spetzler-Martin Grade — Scale estimating AVM surgical risk.

Action Items / Next Steps

• Review additional lectures on other types of brain vascular malformations.
• Practice identifying AVM features and risk factors on sample CT/MR/DSA images.
• Record key AVM characteristics in imaging reports as highlighted.