Amongst the most feared complications of a brain AVM is that it might bleed at some point. Such haemorrhage is not inevitable but when it occurs it is usually reason to consider definitive treatment of the malformation. The most common symptom of haemorrhage is a sudden-onset of severe headache which may be accompanied by nausea and/or vomitting.
Risk of Bleeding
Risk of a First Hamorrhage
Evidence analysed by the MARS consortium currently estimates the risk of a first ever haemorrhage at about 1.3% per annum (95% CI 1.0%-1.7%). Given the variation in the architecture from one malformation to the next, there is likely to be different risks of haemorrhage from one to another given the differing stresses the malformation is subjected to. Therefore one needs be careful in generalising these population statistics to the individual one must emphasise these are estimates not predictions of the future.
This represents a lower figure than has tended to be quoted in the past. This approximation of the risk of first bleeding events has been endorsed by another systematic review and subsequently by prospective data from the TOBAS registry study although those data also suggested that larger more complex AVMs might be associated with greater lifetime risk of bleeding.
Risk of Subsequent Repeated Haemorrhage
If a haemorrhage occurs and the patient recovers, the risk of subsequent bleeding of the AVM remains higher than it was before. It may be greatest in the first twelve months following a haemorrhage with some studies estimating a risk of second haemorrhage between 10 and 20% during that that first year. The baseline risk if second haemorrhage seems to settle at about 4.8% per annum (95% CI 3.9%-5.9%).
Consequences of Bleeding
Brain haemorrhage of any type constitutes a serious illness. The outcome following AVM bleeding may be more variable than most other types because the resulting brain injury is affected by not only the location of the malformation but where it originates from artery, vein or nidus.
Based on a review of the published literature overall the risk of death an AVM haemorrhage is about 9% (95% CI 5-15%). The likelihood of death OR surviving with a physical disability is estimated at 42% (95% CI 33-51%).
Treatment of a Ruptured AVM
Bleeding from an AVM is a medical emergency. The first priority is to stabilise the patient's vital functions just as one would following any other type of stroke.
Urgent transfer to the nearest emergency department is appropriate where oxygen can be administered and intravenous access set up. Most hospitals with an emergency department will be able to carry out a CT scan and establish that a brain haemorrhage has occurred. The medical team there would then contact their nearest neurosurgical unit for advice. If seizures have occurred, anti-epileptic medication will be administered. If conciousness is severely impaired it may be necessary place the patient on a ventilator to stabilise their condition and preserve oxygen delivery to the brain.
Urgent transfer to the nearest emergency department is appropriate where oxygen can be administered and intravenous access set up. Most hospitals with an emergency department will be able to carry out a CT scan and establish that a brain haemorrhage has occurred. The medical team there would then contact their nearest neurosurgical unit for advice. If seizures have occurred, anti-epileptic medication will be administered. If conciousness is severely impaired it may be necessary place the patient on a ventilator to stabilise their condition.
Emergency neurosurgery is usually either to relieve hydrocephalus or address a life-threatening blood clot. Hydrocephalus is usually treated with placement of a drain into the ventricles of the brain and the removal of cerebrospinal fluid will effectively lower the intracranial pressure.
A blood clot large enough to press on the brain, impairing consciousness will usually require removal as an emergency. Such clots are usually adjacent to the arteriovenous malformation nidus.
It is not usually necessary to attempt removal of the AVM at the same time. In the wake of recent haemorrhage the brain is likely to be very swollen and vulnerable. The malformation is also likely to be more difficult to deal with surgically than it would otherwise be leading to an increased risk of partial removal. The day-to-day risk of further bleeding from the nidus is usually low enough to favour limiting surgery to life-saving relief of high pressure with a plan to treat the AVM definitively once the patient has recovered a little. There are situations when bleeding from the AVM will mandate its removal immediately so this is always prepared for as an eventuality.
Once stabilised a digital subtraction angiogram will be carried out to see the AVMs architecture in detail and consider treatment alternatives. If any aneurysm likely to be the source of bleeding is identified endovascular treatment of this will be considered to reduce the risk of rebleeding in the short to medium term.
Definitive treatment of the AVM will remove the risk of further haemorrhage if the arteriovenous shunt can be completely obliterated. This is typically accomplished by microsurgical removal or, for certain types of AVM endovascular embolisation. Stereotactic radiosurgery will require a lead time of several years to accomplish obliteration so is not usually the first recommendation in that circumstance although it may be considered if the procedural risks of other treatments exceed the threat of further bleeding. You can read more about these treatments using the links below.
