Diagnosis of an Unruptured Brain AVM
Increasingly brain AVMs are first discovered when an individual undergoes cross-sectional imaging of the brain with CT or MR for an unrelated reason. Access to high-quality imaigng has become much more widespread and cost-effective. it is estimated that AVMs are present in 0.15% of the population. The discovery that an AVM is present may pose a series of difficult questions for someone who has no symmptoms caused by it. After all the risks we estimate that an AVM might believed may not be realised for many years in the future if indeed they are realised at all.
Should you be concerned that you might harbour an AVM (or any other central nervous system disease) because a relative has been diagnosed we strongly recommend you speak with a specialist about your concerns before undergoing imaging. If you are considering undergoing health-screening imaging pre-scan counselling regarding unexpected asymptomatic discoveries should form part of the process.
The Evidence Base for Treating Unruptured AVMs
The medical profession describes research publications that consider a treatment's efficacy and safety as the evidence base. Most of the time your doctor would wish their decision to deliver treatment to be supported by the results of randomised controlled trials (RCTs). Ideally a treatment has been proven safe and effective after comparison with a sham treatment (a placebo) or with no treatment at all. For example the carotid endartrectomy operation has been demonstrated in several RCTs to reduce the lifetime risk of stroke in selected patients with narrowings of the internal carotid artery in the neck. It is very difficult however to carry out RCTs in a rare condition such as BAVM as there is a smaller pool of patients willing to randomly undergo treatment or live with their condition. Another challenge is to ensure one is "comparing apples with apples". That is to say because AVMs tend to vary in their size and architecture, one individual's AVM may have a different risk of bleeding to anothers
Nonetheless one attempt has been made to do this for brain AVM and the results published as A Randomized trial of treatment for Unruptured AVM or the ARUBA trial". The trial was halted when it became apparent that neurological worsening or death was three times more prevalent in treated patients compared to those only observed. The interpretation of this result was that the evidence did not therefore support treatment of an unruptured AVM. The trial methodology had many critics however. The end-point of complete obliteration of an AVM was not reached for many patients which may have explained some of the observed complications. Most patients were treated with radiosurgery or endovascular techniques when one would have anticipated from the reported characteristics of the AVMs that surgical treatment would have been an appropriate means of completely treating them. Many specialist in the treatment of AVM had significant reservations regarding this interpreatation of the result.
The ARUBA trial has not however been the only research to suggest observation is safer than proactive treatment for unruptured BAVM. The New York Islands AVM study identified the uncertainty as to wheter treatment was necessarily superior to observation and was an inspiration to conduct the ARUBA trial. The Scottish Intracranial Vascular Malformation Study (SIVMS) reported a similar conclusion to ARUBA although many of the same criticisms regarding the treatment selection and completeness of follow-up could be levelled as they were at ARUBA. Models have been developed which allow more accurate advance projections of risk and of prospects of success for both microsurgery and stereotactic radiosurgery which should allow improved patient selection and ensure the AVM is completely treated as safely as possible. It is the view of many specialising in this field that the question as to wheter selected patients benefit from proactive treatment of unruptured BAVM remains unanswered.
What research has taught us is that the treatment of an unrutured brain AVM is undoubtedly assosciated with significant risks that require careful weighing when making a decision to proceed. Results are best when treatment is in the hands of experienced multidisciplinary teams dealing with the disease on a regular basis.