What Does Growth of an Unruptured Brain Aneurysm Mean?

If a follow-up scan shows that your unruptured brain aneurysm has grown, it does not mean it is rupturing right now ^[1]. However, confirmed growth is an important warning sign. It indicates that the aneurysm’s risk of rupturing in the future has increased compared to an aneurysm that remains completely stable ^[1][2].

Because of this increased risk, finding out your aneurysm has grown means you should promptly contact the doctor who ordered the scan to get a referral to a cerebrovascular specialist (a neurosurgeon or a neurointerventionalist who specializes in brain blood vessels) ^[3]. As long as you feel well and have no new symptoms, this is an urgent outpatient priority, not a 911 emergency ^[3].

Confirming the Growth

The first step is for a specialist to confirm that the aneurysm actually grew. A reported change of 1 millimeter (mm) on a scan could be real growth, but it can also simply be a slight difference in how the scan was measured, the angle of the image, or the type of machine used ^[4][5].

While the written radiology report is an important starting point, the treating specialist should ideally compare the actual source images from your recent scan side-by-side with your previous ones ^[5]. By looking at the images directly using comparable measurements, the specialist can determine if the aneurysm’s size or shape has genuinely changed ^[4].

Understanding the New Risk

It is impossible to predict exactly when or if an aneurysm will rupture, but growth increases the odds. In a large international study, aneurysms that grew by at least 1 mm had an estimated average rupture risk of 4.3% in the year following the growth ^[1]. For comparison, stable aneurysms had a much lower rupture rate of roughly 0.1% per year ^[2].

These are group averages, not your personal risk. While the 4.3% figure shows a meaningful increase in risk, it also means that the vast majority of growing aneurysms in the study did not rupture in that first year ^[1]. Your individual risk depends on several factors ^[1][6]:

• Size: Larger aneurysms (such as those 7 mm or larger) generally carry higher risk, though smaller aneurysms can and do rupture ^[1].
• Shape: Aneurysms that develop an irregular shape or a “daughter sac” (a small blister on the aneurysm) have a higher risk ^[1].
• Location: Aneurysms in certain blood vessels (like the posterior circulation or anterior communicating artery) are more prone to rupture ^[1].
• Personal Factors: High blood pressure, current smoking, a family history of aneurysms, or a personal history of a previous aneurysm rupture all increase risk ^[6].

Reassessing Your Care Plan

When an aneurysm grows, your care team will re-evaluate your treatment options ^[3]:

• Preventive Procedure: Your team may recommend repairing the aneurysm if the new risk of rupture outweighs the risks of the procedure itself ^[3][6]. Options may include surgical clipping (placing a tiny metal clip across the base of the aneurysm during open surgery) or endovascular treatments like coiling (filling the aneurysm with tiny wires via a catheter), stenting, or flow diversion (using a mesh tube to direct blood flow away from the aneurysm) ^[7]. Each approach has different risks, including stroke, bleeding, or the need for follow-up treatments, and your anatomy determines which options are possible ^[7].
• Closer Surveillance: If the growth is very slight, or if procedural risks are high due to your anatomy or overall health, your doctor may recommend repeating the scan much sooner to closely track its behavior ^[3].
• Lifestyle Factors: Controlling your blood pressure and completely stopping smoking may reduce your risk of further growth and rupture ^[3]. Ask for support to quit smoking, and do not stop or change your blood pressure medications without speaking to your doctor.

When to Seek Emergency Care

Even if you are scheduled for a specialist visit, call 911 (or your local emergency number) immediately and do not drive yourself if you experience any signs of a possible rupture ^[8][9]. Seek emergency care for any of the following:

• A sudden, severe “thunderclap” headache (often described as the worst headache of your life) ^[8]
• Stiff neck ^[10]
• Nausea and vomiting accompanied by a sudden headache ^[10]
• Fainting, confusion, or loss of consciousness ^[11]
• Sudden weakness, numbness, difficulty speaking, or sudden changes in your vision (such as a drooping eyelid, unequal pupils, or double vision) ^[11]