The Hidden Cost of Watchful Waiting: Why Small Aneurysms Deserve Big Conversations
Most unruptured brain aneurysms are small. For years, the traditional advice for small aneurysms has been to “watch and wait.” However, for many patients, this leads to prolonged uncertainty and sometimes preventable harm.
At the Brain Aneurysm Center at Atlantic Brain and Spine (ABS), we believe that small aneurysms deserve early and thoughtful attention. Emerging research and clinical experience tell us size isn’t the whole story. That’s why, when you’re navigating the impact of a brain aneurysm diagnosis, it’s essential to see true subspecialists – expert surgeons who understand the nuances of aneurysm care and can guide you toward the best possible outcome.
The 7 Millimeter Threshold: Where We’ve Been
For decades, the 7-millimeter mark has guided treatment decisions. Aneurysms smaller than that were typically monitored, while larger ones were treated. The goal was to balance the risks of intervention with the perceived risk of rupture.
Two of the most common treatment options for unruptured aneurysms are:
- Surgical clipping: An open brain procedure in which a neurosurgeon places a small metal clip at the aneurysm’s base to stop blood flow.
- Endovascular Coiling: A minimally invasive technique that threads tiny platinum coils into the aneurysm to promote clotting.
While often effective, these procedures carry risks of complication. On the other hand, a rupture can have catastrophic consequences, including stroke, permanent neurological damage, or even death.
Current Guidelines: Where We Are Now
Updated guidance from the American Heart Association and American Stroke Association emphasizes a more comprehensive approach. Instead of focusing on size alone, doctors are encouraged to consider:
- Aneurysm characteristics: Size, shape, location, and documented growth
- Patient history: Age, blood pressure, smoking status, and overall health
- Family history of aneurysms
- Number of aneurysms present
- Underlying conditions such as arteriovenous malformations or genetic disorders
Yet in practice, many patients are still told to wait.
Dr. Kyle T. Chapple is a neurosurgeon specializing in brain aneurysms at ABS. Dual-trained in open microsurgery and advanced endovascular techniques, he delivers personalized care that looks beyond size to enhance patient outcomes.
“I often see patients who were initially told their aneurysm was low risk because of its small size,” said Dr. Chapple. “But when we look more closely, that’s not always the case. Every aneurysm deserves careful evaluation and an individualized treatment plan.”
What the Latest Data Tells Us
Emerging research reveals that small aneurysms do rupture.
A study in World Neurosurgery analyzed 628 cases of ruptured aneurysms. Seventy-five percent of the ruptured aneurysms were smaller than 7 millimeters, and nearly half were under 5 millimeters. Most of these aneurysms were deemed low risk by a modern scoring tool called PHASES, which estimates rupture risk based on population, blood pressure, age, aneurysm size, prior hemorrhage, and location. Despite their low scores, these aneurysms still ruptured, meaning many of these patients would likely have been managed conservatively, with potentially devastating results.
Additionally, a 2023 BMC Neurology study used machine learning to evaluate more than 1,400 small, multiple intracranial aneurysms. Researchers found that patients with a strong family history had rupture risks above 75%, even though the aneurysms were small.
These studies highlight the gap between population-based guidelines and individual patient risk. Two patients with similarly sized aneurysms can face very different outcomes, making personalized care essential.
4 Hidden Costs of Watchful Waiting
Despite these findings, watchful waiting is still commonly portrayed as the safe choice. Unfortunately, for many patients, the true emotional and medical risks are only realized over time.
The Emotional Toll
Living with an untreated aneurysm can lead to ongoing anxiety, uncertainty, and fear. Patients may wonder: Is it growing? Has it changed? What if I miss the warning signs? Without regular, expert follow-up, watchful waiting can feel like gambling with your future.
Missed treatment windows
Some small aneurysms are easier and safer to treat early before they grow, change shape, or rupture. Waiting too long can mean missing the best chance for minimally invasive treatment.
“When we catch aneurysms early, we can often treat them with minimally invasive procedures that carry less risk and offer a quicker recovery,” said Dr. Chapple. “However, as an aneurysm grows and changes, those options can become more limited.”
Higher long-term costs
When rupture occurs, emergency care is more complex and more expensive.
Gaps in follow-up
Effective monitoring requires consistent imaging and follow-up by experienced specialists. Not all patients have access to this level of care, leading to missed warning signs.
A Better Way Forward: Individualized Risk Stratification
Instead of relying on size alone, we now have tools and knowledge to assess rupture risk more precisely.
What Imaging Can Reveal
Advanced imaging allows specialists to detect more subtle warning signs. A 2024 study of more than 4,700 small aneurysms found several features that raised rupture risk, including:
- Shape and structure: Aneurysms that are tall and narrow, or have a wide base, were more likely to rupture.
- Branch points: Aneurysms at vessel splits (bifurcations) also carried higher risk.
- Irregular appearance: Bulges or small side pouches (daughter sacs) suggest a weaker vessel wall.
- Low resistance or pressure: Abnormal blood flow patterns and thinning walls (measured by “pressure loss” and “wall shear stress”) were strong predictors of rupture.
Location matters.
Some areas of the brain are riskier than others. Aneurysms in the anterior communicating artery (which connects the front parts of the brain), the posterior communicating artery (which links the front and back of the brain), and the top of the basilar artery (located deep in the brainstem) carry a higher chance of rupture, even when small.
“Where an aneurysm is located can change everything,” said Dr. Chapple. “We take that into account along with other factors to decide when treatment makes sense.”
For example, one patient was referred to ABS after a 4mm aneurysm ruptured—despite being previously labeled low risk due to its small size. It was located at the top of the basilar artery, a deep and delicate area of the brain where ruptures can be devastating. “Had that aneurysm been in a less risky location, the watch-and-wait approach might have held up,” Dr. Chapple said. “But in this case, the location significantly increased the risk. That case reinforced how important it is to look beyond size and consider the full anatomical and patient risk profile.”
In another case, a woman in her 40s came to us with a 3mm aneurysm on the anterior communicating artery (ACom)—a common rupture site. Though tiny, it had an irregular shape and she had a strong family history of aneurysms. “Those details changed our thought process,” said Dr. Chapple. “We opted for early treatment with coiling, and her follow-up imaging showed early changes that confirmed we made the right call. It’s exactly the kind of case that proves size is only one piece of the puzzle.”
Scoring tools have limits.
Modern risk scoring tools like PHASES and UIATS (unruptured intracranial aneurysm treatment score) can help guide decisions, but they aren’t foolproof. In fact, a European Journal of Neurology study found that UIATS flagged fewer than half of the aneurysms that later grew or ruptured, meaning many at-risk patients might be overlooked if we rely on scoring tools alone.
Collaboration improves outcomes.
When experts come together, patients gain more than a treatment plan, they gain peace of mind. Successful aneurysm care requires specialized skill in both complex microsurgical procedures, such as aneurysm clipping and bypass, and minimally invasive interventions like coiling and flow diversion.
Small aneurysms should never be dismissed without a thorough, personalized evaluation. Here’s how we need to shift the conversation:
- Educate referring doctors. Aneurysm care shouldn’t rely on size alone. Early referral allows specialists to make more informed decisions.
- Empower patients. Living with an aneurysm shouldn’t mean living in fear. Patients deserve clear communication and a plan that evolves with them.
- Build stronger systems. Nearly 25% of ruptured aneurysms are misdiagnosed at first, often because no scan was performed. Consistent imaging protocols could change that.
Even Small Aneurysms Can Carry Big Consequences
Size is only one part of the story. Oversimplifying the risk of small aneurysms can lead to missed opportunities for timely care.
At ABS, we treat every aneurysm with the attention it deserves. Through advanced imaging, collaborative care, and individualized treatment plans, we help patients move from uncertainty to clarity.
Concerned about an aneurysm diagnosis? Let’s talk. Schedule a consultation.
