A nidus of vessels with early venous drainage; the Spetzler–Martin grade needs size, eloquence and deep venous drainage — and the report looks for the high-risk features (intranidal aneurysm, venous stenosis, deep drainage) and haemorrhage.
Orient first
- Spetzler–Martin: size (< 3, 3–6, > 6 cm), eloquent cortex, deep venous drainage (verify the grading version).
- Haemorrhage risk rises with previous haemorrhage, deep location, exclusively deep venous drainage and associated aneurysms.
- Catheter angiography remains the reference for angioarchitecture.
Acquire the study
- T2, SWI, time-of-flight and contrast-enhanced MRA, post-gadolinium T1.
The manoeuvre
- T2: serpiginous flow voids — the nidus; measure its maximal diameter in cm.
- Relation to eloquent cortex (sensorimotor, language, visual, internal capsule, brainstem).
- Draining veins: superficial vs deep (internal cerebral, basal vein, vein of Galen).
- SWI: old haemorrhage; FLAIR: gliosis around the nidus.
What confirms it
- A nidus with early venous drainage; catheter angiography confirms and grades.
What licenses you to exclude it
- Normal MRI with MRA excludes a macroscopic AVM; micro-AVMs may still be angiographically occult.
The classic misread
- A haematoma compressing the nidus hides it — repeat imaging after resorption.