What are the risks that bleeding would occur?
There is uncertainty as to what precisely the risk of bleeding from an AVM is as we cannot know how many individuals live a full life without their AVM ever bleeding. Furthermore each AVM is somewhat different in terms of it's architecture meaning that the stresses and strains on the blood vessels involved may differ from one individual to the next. One should therefore be cautious in extrapolating from population statistics to the individual.
The best quality data currently available suggests that the risk of a first haemorrhage from a brain AVM lies between 1.2 to 2.2% per annum approximately. Increasing age and a history of previous haemorrhage are confer a higher risk of bleeding. The risk of a second haemorrhage occurring is estimated at 4.4% per annum on average.
Each episode of bleeding poses a risk to ones life and a risk of conferring or compounding disability. It is not possible to be specific as to the level of such disability in advance.
Why does an AVM bleed?
Bleeding from an AVM may originate from a number of sites. Aneurysms are balloon-like dilatations that develop on walls of bloods vessels often as a result of "wear and tear" over time. Aneurysms may develop on the arteries carrying blood to an avm. They may develop within the substance of the nidus itself and on the veins carrying blood away from the malformation. Aneurysms on the arteries irrigating the AVM are sometimes termed flow aneurysms and should they rupture blood is released primarily into the cerebrospinal fluid (CSF) around the brain.
Rupture of a nidal aneurysm is more likely to produce a blood clot within the brain itself. Rupture of a venous aneurysm typically results in blood within the CSF containing ventricles. In reality if the bleeding is of sufficent volume blood may be located within any of these spaces concurrently.
Another reason that the nidus of an AVM may rupture is that the veins draining the malformation become obstructed. This can result from blood clot (thrombosis) developing in said vein. Should there not be sufficent redundant outlets for the blood flow the resulting pressure build-up in the nidus can be enough to cause bleeding. Blocakages of veins may be complete and sudden o may be partial producing a venous stenosis that may be demonstrated on imaging. Unfortunately it is not possible to be precise as to the risk posed by such a feature when observed.
How is bleeding Managed?
A 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, oxygen is administered and intravenous access set up. Most hospitals with an emergency dempartment will be able to carry out a CT scan and establish that a brain haemorrhage has occurred. The meidcal team their would then contact their nearest neurosurgical unit for advice.
A few individuals suffering a sudden catastrophic haemorrhage may be beyond help and for that reason are not transferred to the neurosurgical centre. The neurosurgical team's priority will be to control the pressure exerted by bleeding inside the head if that is possible to do. This may mean that the patient is maintained in a medically induced coma. A small tube (external ventricular drain) may be placed to remove cerebrospinal fluid thus reducing pressure. Larger blood clots that are pressing on vital structures may need to be removed. It is usually the case that any assosciated AVM will not be removed at the same time as it is frequently safest to address the blood clot then allow the brain to recover before returing to deal with the AVM. There are occasions when the AVM needs to be addressed surgically at the same sitting and that is a decision for the operating team at the time. Learn more about the surgical removal of an AVM as well as the other means of treatment by consulting the menu on the right of this page.