Incidentally discovered aneurysms in the brain-what to do about them?

Incidentally discovered aneurysms in the brain-what to do about them?


Nitin K Sethi, MD

Assistant Professor of Neurology

New York-Presbyterian Hospital

Weill Cornell Medical Center

New York, NY 10065




Recently I saw a patient in my office. She had undergone a MRI scan for headache. The MRI scan revealed a 4 mm aneurysm in the left middle cerebral artery with a 2 mm neck. I reassured her that the aneurysm was not the cause of her headache and that she more than likely had migraine headaches when she asked me the million dollar question which I had been expecting all along.

Dr. Sethi, but what to do about the aneurysm? Can it rupture? Do I need surgery to take care of it she asked me? I answered her questions according to the best scientific evidence I had at my disposal. That patient visit though got me thinking about how many patients face the same dilemma. That is the purpose of this post. When aneurysms are discovered incidentally in the brain, what needs to be done?

In keeping with my style of writing, I shall keep this simple. Simply put when an aneurysm is discovered in the brain, there are 2 avenues open to us.


Avenue 1. DO NOTHING (otherwise called the WAIT AND WATCH policy). The aneurysm may never rupture in the patient’s lifetime so why touch it. The wait and watch policy works best for aneurysms which are small in size (less that 5 mm in size, some books say aneurysms less that 7 mm in size may be safety observed). Small sized aneurysms in hard to reach areas of the brain can be justifiably observed. What do I mean by hard to reach areas of the brain? Let me explain with the aid of an example. Let us assume Kim our fictitious patient has a 3 mm aneurysm in the cavernous portion of the left internal carotid artery. This is the portion of the internal carotid artery that traverses the cavernous sinus. Now this area is difficult to reach “safely” by the neurosurgeon. The risks of surgery are tangible and may outweigh the potential benefits (remember as the aneurysm is small in size the risk of rupture is low). Better to wait and watch rather than go about chasing this aneurysm.

I said WAIT AND WATCH not WAIT AND FORGET. Meaning the patient should be advised to remain in follow up. The aneurysm should be followed by serial MRI scans done at intervals varying from 6 months to 1 year. Initially the follow up is more frequent, once we have documented that the aneurysm is not increasing in size, the scans can be repeated less frequently. If the aneurysm starts increasing in size then a more “active” course can be pursued. If the patient is hypertensive, good blood pressure control should be the goal as risk of aneurysm growth and rupture increases if blood pressure remains elevated.


Avenue 2. PURSUE AN ACTIVE STRATERGY. Simply put it means “taking care” of the aneurysm surgically either via open craniotomy or via an endovascular approach. Let me explain this. Let us assume Kim has a 10 mm sized aneurysm is the right middle cerebral artery territory. We can approach this aneurysm in 2 ways. First is via an open craniotomy, meaning that open up the skull (we call this a craniotomy), visualize the aneurysm and then secure it with a clip or a band. Once the aneurysm is clipped it cannot rupture as it is excluded from the circulation. PROBLEM SOLVED!!!


Second approach is via an endovascular route. No craniotomy is required. The endovascular surgeon or the interventional neuroradiologist threads a catheter via the femoral artery in the groin and reaches the aneurysm in the brain. Once there he coils it (coils of platinum coated with a thrombogenic material are deployed inside the aneurysm). Over time the aneurysm clots and seals itself from the circulation. PROBLEM SOLVED!!!


Broadly speaking endovascular coiling is superior to open craniotomy (at least in some respects). As no craniotomy is required hospital stay is shorter and post-operative recovery quicker. The endovascular surgeon can reach areas where the neurosurgeon may fear to tread. Certain aneurysm though are not amenable to coiling (example those with a broad neck as the coils fall out). Also once an aneurysm is coiled it takes time before it gets completely thrombosed, surgery on the other hand takes care of the problem then and there.

Incidental cerebral aneursym on brain imaging: what to do?

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.

Personal Regards,

Nitin Sethi, MD