Neurologic
Brain arteriovenous malformation
A tangle of abnormal brain vessels that radiosurgery gradually seals off over two to three years, eliminating the risk of bleeding.
Definition
A cerebral arteriovenous malformation (AVM) is a congenital nest of direct artery-to-vein connections without a normal capillary bed in between. High-pressure flow through the nidus can rupture and cause intracerebral hemorrhage, seizures, headaches, or progressive neurologic deficits. Rupture risk is roughly 2–4% per year, and management depends on size, location (eloquent versus non-eloquent brain), and venous drainage pattern.
How radiation treats it
Radiosurgery triggers progressive endothelial proliferation and hyalinization within the nidus, gradually thrombosing and obliterating the malformation over two to three years (the "latency period"). Once fully obliterated, the bleeding risk is essentially eliminated. Radiosurgery is favored for small-to-medium AVMs in deep or eloquent locations where surgery or embolization alone would carry unacceptable risk of stroke or deficit.
Side effects
- Headache, nausea, or lethargy in the days after treatment are usually self-limited.
- Seizure risk persists and even rises during the latency period — patients must be counseled that protection is not immediate.
- Radiation necrosis or symptomatic edema occurs in a minority, and permanent new deficits are possible when the nidus sits in eloquent brain.
Simulation process
A stereotactic frame is applied, and both MRI and catheter angiography are fused to the stereotactic CT to define the nidus precisely — the angiogram is essential because it shows the true extent of shunting that MRI can underrepresent. The nidus is contoured with no margin, and eloquent cortex, brainstem, optic pathway, and any prior hemorrhage cavity are contoured as constraints. Plan quality is judged by conformality and the steepness of dose fall-off outside the nidus.
Treatment process
Single-fraction radiosurgery to 16–20 Gy at the nidus margin, selected to balance obliteration rate against toxicity (larger lesions receive lower doses or are treated with staged volume, pre-embolization, or fractionated regimens). One session delivers the entire treatment. Follow-up is MRI at yearly intervals, with catheter angiography after 2–3 years to confirm complete obliteration — the only definitive proof that the bleeding risk is gone.
Key takeaways for students
- Obliteration takes 2–3 years, and hemorrhage risk persists during that latency.
- Angiography defines the nidus and confirms the cure.
- 16–20 Gy margin dose — smaller and compact niduses obliterate best.