Brain Arteriovenous Malformation

A brain arteriovenous malformation is an abnormal tangle of arteries and veins (the nidus) with direct arteriovenous shunting and no intervening capillary bed. It causes intracranial haemorrhage, seizures and neurological deficits, and is a leading cause of haemorrhagic stroke in young adults.

Detection rate is about 1 in every 100,000 people each year, and prevalence about 10 to 18 in every 100,000. Most present between 20 and 40 years of age. Haemorrhage is the first presentation in about half.

Associations. Hereditary haemorrhagic telangiectasia (ENG and ACVRL1), RASA1 capillary malformation arteriovenous malformation syndrome, and associated flow related aneurysms in 10 to 20%.

Haemorrhage risk. Annual rupture risk is about 2 to 4% overall; higher after a previous rupture (up to 6 to 10% in the first year), with deep location, deep venous drainage only, and associated aneurysm.

Grading. Spetzler-Martin grade (1 to 5): size under 3 cm = 1, 3 to 6 cm = 2, over 6 cm = 3; eloquent location = 1; deep venous drainage = 1. The supplementary score adds age, diffuse nidus and compactness.

Pathophysiology.

Abnormal embryonic vascular development, with somatic KRAS or related signalling variants in sporadic lesions, creates a low resistance shunt.

Arterialised veins and high flow cause vessel wall stress, rupture and venous hypertension, with steal causing local ischaemia.

• Intracerebral or intraventricular haemorrhage with sudden headache, deficit or reduced consciousness.
• Seizures, focal or generalised, in about 30%.
• Chronic headache, progressive deficit or pulsatile tinnitus; a bruit is rare.
• Incidental finding on imaging in a minority.

Red flags.

• Sudden severe headache or deficit (haemorrhage).
• New seizure or status epilepticus.
• Progressive neurological decline with a known malformation.

• Non-contrast CT for acute haemorrhage, with CT angiography.
• MRI and MR angiography to map nidus, eloquent cortex and venous drainage.
• Digital subtraction angiography is the reference test to define the nidus, feeding arteries, flow related aneurysms and venous drainage, and is needed before treatment.
• Screening for hereditary haemorrhagic telangiectasia when multiple lesions or a family history is present.

Differential diagnosis. Cavernous malformation, dural arteriovenous fistula, venous malformation, haemorrhagic tumour, aneurysm, amyloid angiopathy and moyamoya disease.

• Ruptured malformations: usual intracerebral haemorrhage care, blood pressure control and neurosurgical review, with treatment of the malformation after stabilisation.
• Unruptured malformations: randomised data show worse short term outcomes with intervention than with medical care, so decisions are individualised by grade, age and patient preference. Spetzler-Martin grades 1 and 2 are often treated by surgery; small deep lesions by radiosurgery; embolisation is mainly adjunctive.
• Surgical resection gives immediate cure with an obliteration rate over 95% in low grade lesions.
• Stereotactic radiosurgery obliterates about 70 to 80% of lesions under 3 cm over 2 to 3 years, with haemorrhage risk persisting during the latency.
• Seizures: levetiracetam 500 mg orally twice daily, increased as needed to a maximum of 1500 mg twice daily; continue for at least 2 years after the last seizure for treated patients. Monitor mood, behaviour and renal function. Reduce dose when creatinine clearance is 50 to 80 mL/min (500 to 1000 mg twice daily), 30 to 50 mL/min (250 to 750 mg twice daily) and under 30 mL/min (250 to 500 mg twice daily).
• Control blood pressure to under 130/80 mmHg; avoid antithrombotic drugs unless a clear indication exists; counsel on exertion and Valsalva.

Monitoring. After surgery, a confirmatory angiogram. After radiosurgery, MRI at 6 to 12 months and angiography at 3 years. Conservative management needs yearly clinical review and imaging every 1 to 2 years initially.

Referral and escalation. Specialist neurovascular centre for all patients; emergency neurosurgical review for haemorrhage.

Special groups. Pregnancy: haemorrhage risk is not clearly increased; delivery mode follows obstetric indication, with neuroanaesthetic planning. Children: higher lifetime risk, so treatment is considered earlier.