At times an incidental cerebral aneurysm is found when neuroimaging is carried out. Let me explain this with an example. You go to your doctor as you have been having headaches or suppose you have a history of migraine, your doctor orders a MRI brain. A cerebral aneurysm is found on brain imaging.
What to do now is the question?
Does the aneurysm warrant treatment?
If yes what treatment?
To answer the above questions it is essential to first understand the natural history of cerebral aneurysm. An aneurysm is a dilatation of a blood vessel. These dilatations may be congenital (meaning you are born with it) or they may develop later in life due to trauma or turbulent blood flow. Cerebral aneurysms can rupture. When they do rupture they cause bleeding into the brain. This bleeding occurs into the subarachnoid space and hence it is called subarachnoid hemorrhage (SAH). SAH has a high morbidity and mortality and hence it is essential that if an incidental aneurysm is found we should know what to do about it.
Well first the question is whether the aneursym is indeed the cause of the symptom for which the imaging was done in the first place. As I stated earlier, the aneurysm may be entirely unrelated to the headache and may just be an incidental finding.
If the aneursym is incidental then the question is what needs to be done about it. What is the risk that it would rupture and cause hemorrhage? How soon should it be taken care of? Fortunately we now have some answers to the above questions. Studies have shown that the risk of rupture is directly related to the size of the aneurysm. Aneurysms which are small in size, less than 7 mm have a lower risk of rupture as compared to those above 10 mm in size. Hence a small aneurysm may be watched. Your doctor may opt to do nothing apart from recommending that the MRI scan be repeated after 6 months to 1 year. If there is interval increase in size of the aneurysm, then definitive treatment options can be pursued.
For aneuryms which are larger than 10 mm, it is important that they be treated on an urgent basis as the risk of rupture is high. There are different modalities to treat the aneurysm. One may either opt for endovascular coiling (here the skull is not opened, instead the aneurysm is approached via the endovascular route and then thrombogenic coils are placed into the aneurysm. The idea is to thrombose the aneurysm over time and hence to obliterate it). The other more invasive approach is to do a formal surgery, the skull is opened up, the aneurysm is located by the neurosurgeon and then a clip or band is placed across its neck to obliterate it.
Which option should be employed depends upon the aneurysm characteristics. Aneurysms which have a broad neck are difficult to coil, those which are in surgically inaccessible locations are more easy to coil endovascularly.
Hope this helps some of my readers. It is a beautiful Sunday afternoon here in New York City. Time to go for a run.
Nitin Sethi, MD