Cerebral Arteriovenous Malformation
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Direct answer
A cerebral arteriovenous malformation is a congenital tangle of abnormal arteries and veins joined directly through a nidus, without an intervening capillary bed. It most often presents with intracranial haemorrhage or seizures, and the bleeding risk is the main reason for treatment. Spetzler-Martin grading, based on size, eloquence and deep venous drainage, predicts surgical risk and guides the choice between surgery, embolisation and radiosurgery.
What you must remember
- Architecture: a nidus of abnormal vessels with direct arteriovenous shunting, so the high-pressure arterial flow enters the venous system without a capillary bed.
- Presentation: haemorrhage is the commonest presentation in adults, with seizures, headache and focal deficits as the other common modes.
- Bleeding risk: unruptured lesions carry a lower but continuing annual risk of haemorrhage, which is the main long-term concern.
- Spetzler-Martin grade: a sum of three scores, size (under 3 cm scores 1, 3 to 6 cm scores 2, over 6 cm scores 3), eloquent location (1) and deep venous drainage (1), giving grades I to V.
- Surgical risk: grades I and II carry low surgical risk, grade III moderate risk, and grades IV and V high risk, so they are often managed without immediate surgery.
- Embolisation: endovascular embolisation is usually adjunctive before surgery or radiosurgery and rarely cures the lesion alone.
- Radiosurgery: stereotactic radiosurgery suits small or deep lesions, with obliteration taking two to three years.
- Imaging: MRI with contrast shows the nidus and prior bleeds, while digital subtraction angiography defines the feeding arteries and venous drainage.
Grading a lesion before choosing treatment
A 26-year-old man presents with a lobar haemorrhage, and angiography shows a 4 cm nidus in the non-dominant temporal cortex with superficial venous drainage. Grading the lesion is the step that decides the treatment pathway.
- Confirm the angioarchitecture: Digital subtraction angiography defines the nidus, the feeding arteries and the venous drainage before any treatment is chosen.
- Score the size: A 4 cm lesion is medium and scores 2, since small lesions score 1 and large lesions over 6 cm score 3.
- Score the location and drainage: A non-dominant temporal nidus is non-eloquent and has superficial drainage, so each scores 0.
- Assign the grade: The total of 2 gives grade II, which carries low surgical risk.
- Choose the treatment: Microsurgical resection is the usual option for a low-grade lesion, with embolisation as an adjunct, and radiosurgery is kept for high-risk or deep lesions.
In this patient the grade is II, so surgical resection is usually preferred. The same scoring applied to a deep, eloquent lesion would move the grade up and change the answer.
Where the exam tries to catch you
Most lost marks come from treating the grade as a fixed prognosis or misreading the role of embolisation.
- Trap: Operating on every unruptured AVM because it might bleed. Correct: The ARUBA trial suggested that medical management alone can outperform intervention in selected unruptured lesions, so risk must be weighed.
- Trap: Taking a grade V lesion to mean immediate surgery is needed. Correct: High-grade lesions are usually managed without immediate surgery, often with radiosurgery or observation.
- Trap: Calling embolisation a cure. Correct: Embolisation alone rarely obliterates an AVM, so it is usually an adjunct before resection or radiosurgery.
- Trap: Confusing a vein of Galen malformation with an ordinary AVM. Correct: Vein of Galen malformation is a neonatal high-flow shunt presenting with heart failure, not adult haemorrhage.
Frequently asked questions
What is the Spetzler-Martin grade of a cerebral AVM?
The Spetzler-Martin grade is the sum of three scores: size (1 for under 3 cm, 2 for 3 to 6 cm, 3 for over 6 cm), eloquent location (1 if present) and deep venous drainage (1 if present). Grades run from I to V, and higher grades carry greater surgical risk.
What is the commonest presentation of a cerebral arteriovenous malformation?
Intracranial haemorrhage is the commonest presentation of a cerebral arteriovenous malformation in adults. Seizures, headache and focal deficits are the other common presentations, and haemorrhage is also the main reason for treatment.
Which investigation defines the angioarchitecture of a cerebral AVM?
Digital subtraction angiography defines the angioarchitecture of a cerebral AVM, showing the nidus, feeding arteries and venous drainage. MRI with contrast shows the lesion and any prior haemorrhage but gives less detail of flow.
When is stereotactic radiosurgery used for cerebral AVM?
Stereotactic radiosurgery is used for small or deep cerebral AVMs where open surgery carries high risk. Obliteration is slow, with a latency period of two to three years, so follow-up imaging is needed while the lesion remains active.
How does a vein of Galen malformation differ from a cerebral AVM?
A vein of Galen malformation is a neonatal high-flow arteriovenous malformation that presents with heart failure rather than adult haemorrhage. A typical cerebral AVM is a parenchymal nidus that most often presents in adults with haemorrhage or seizures.