- Arteriovenous malformation (AVM) is a congenital cerebral vascular malformation consisting of:
- Feeding artery or arteries
- Enlarged draining vein or veins
- Hemorrhage (4% per year)
- Steal phenomenon: blood seeks AVM and normal brain paranchyma is inadequately supplied
 Spetzler-Martin Grading System
||Eloquence of adjacent brain
|Small (<3 cm)||1||Noneloquent||0||Superficial only ||0|
|Medium (3-6 cm)||2||Eloquent||1||Deep component ||1|
|Large (>6 cm)||3||…||…|
- Size: Measure the largest diameter of the nidus of the lesion on angiography.
- Eloquence: Eloquent areas include sensorimotor, language, visual, thalamus, hypothalamus, internal capsule, brain stem, cerebellar peduncles, and deep cerebellar nuclei.
- Venous drainage: The lesion is considered superficial only if all drainage is via the cortical drainage system.
 Imaging Findings
Patient #1: MRI demonstrates a large right AVM
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