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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Neurology

Calculating Your Risk: Understanding the Scores

At a Glance

PHASES estimates an unruptured brain aneurysm’s five-year rupture risk, while ELAPSS estimates growth risk at three and five years. Both are population-based guides, so doctors also consider aneurysm shape, growth, smoking, family history, and overall health.

When you are diagnosed with an unruptured brain aneurysm, the most pressing question is often: “What is the chance this will bleed?” To help frame this discussion, doctors use specialized scoring models to estimate risk based on data from thousands of other patients [1].

The two most common tools are the PHASES score, which estimates the risk of rupture, and the ELAPSS score, which estimates the risk of the aneurysm growing over time [2][3].

Important Context: These scores are population-level estimates for selected patients with untreated unruptured aneurysms. They are guides for shared decision-making, not absolute guarantees, and they are not used for acute management if an aneurysm has already ruptured [4].

The PHASES Score: Estimating Rupture Risk

The PHASES score was developed to estimate risk of a rupture over the next five years [5]. It uses six factors:

  • P (Population): Your geographic origin (derived from specific epidemiologic study groups) [5].
  • H (Hypertension): Whether you have a history of high blood pressure [6].
  • A (Age): Your current age [5].
  • S (Size): The maximum diameter of the aneurysm [6].
  • E (Earlier SAH): If you have previously had a subarachnoid hemorrhage from a different aneurysm [6].
  • S (Site): Where in the brain the aneurysm is located [5].

Limitations of PHASES

While PHASES is widely used, it has “blind spots” that require specialist judgment:

  • Shape and Morphology: PHASES does not account for irregular shapes or a daughter sac (a smaller bump on the main aneurysm). Research shows that irregular shapes can increase rupture risk, even in small aneurysms [7][8].
  • Family History: The score does not factor in whether your close relatives have had aneurysms [9].
  • Low Scores Are Not Zero Risk: Many aneurysms that eventually rupture have low PHASES scores. A “low” score does not automatically mandate observation, just as a high score does not automatically mandate intervention [10][11].

The ELAPSS Score: Estimating Growth Risk

Because a growing aneurysm may be more likely to rupture, doctors use the ELAPSS score to help inform surveillance plans [2][12]. ELAPSS estimates the risk of growth at 3 and 5 years using similar factors to PHASES, but importantly includes the shape of the aneurysm (regular vs. irregular) [2].

While ELAPSS helps inform how closely an aneurysm should be monitored, it does not strictly dictate the scan interval [3].

Why Scores Aren’t the Whole Story

Medical scores provide a population average, but they cannot perfectly predict individual outcomes [4]. Your care team will look at factors these scores may miss:

  • Interval Growth: If follow-up scans show the aneurysm is growing, the risk of rupture generally increases [12][13]. However, a tiny difference (e.g., 1 mm) can sometimes fall within measurement variability between scans. Confirmed growth prompts a reassessment of your plan, rather than an automatic trigger for surgery.
  • Smoking: Combustible smoking is one of the strongest predictors of aneurysm growth and rupture, yet it is not a direct part of the PHASES calculation [14].
  • Multiple Aneurysms: If you have multiple aneurysms, your risk profile is more complex than a single score suggests [15].

In short, these models provide a starting point for a detailed conversation with your doctor about your specific anatomy, health history, and treatment preferences [4][16].

Common questions in this guide

What does my PHASES score mean for an unruptured brain aneurysm?
The PHASES score estimates the chance that an unruptured brain aneurysm will rupture within five years. It considers geographic population group, high blood pressure, age, aneurysm size, a previous subarachnoid hemorrhage from a different aneurysm, and aneurysm location. It is a population-based estimate, not a guarantee for one person, and it is not used for emergency care after an aneurysm has ruptured.
What does the ELAPSS score predict?
The ELAPSS score estimates the chance that an unruptured brain aneurysm will grow over three and five years. It uses several factors similar to PHASES and also considers whether the aneurysm has a regular or irregular shape. The result can help with monitoring plans, but it does not set an exact scan interval by itself.
Does a low PHASES score mean my brain aneurysm cannot rupture?
No. A low PHASES score does not mean there is zero rupture risk, and some aneurysms that later rupture have had low scores. Aneurysm shape, family history, smoking, multiple aneurysms, and growth may change the overall assessment, while a high score does not automatically mean surgery is needed.
Why does the shape of a brain aneurysm matter?
An irregular shape or a daughter sac, which is a smaller bulge on the aneurysm, may be linked with greater rupture risk even when the aneurysm is small. PHASES does not fully account for these features, while ELAPSS includes aneurysm shape when estimating growth risk. Your specialist can review these findings on your imaging.
How do smoking and blood pressure affect brain aneurysm risk scores?
High blood pressure is one of the factors included in the PHASES score. Combustible smoking is a strong predictor of aneurysm growth and rupture, but it is not directly included in the PHASES calculation, so doctors consider it separately when discussing risk and care.
Will my score decide how often I need scans or whether I need surgery?
No. PHASES and ELAPSS support shared decision-making but do not automatically determine surgery or the exact timing of follow-up scans. Doctors also consider confirmed growth, aneurysm shape and location, other aneurysms, your overall health, and your treatment preferences.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is my calculated PHASES score, and how does that population estimate apply to my individual health situation?
  2. 2.Does my imaging show any irregular shape or 'daughter sac' that the PHASES score might not fully account for?
  3. 3.How does my family history of aneurysms change the way we interpret my overall risk profile?
  4. 4.If my ELAPSS score suggests a certain growth risk, what does that mean for our specific plan for follow-up scans?
  5. 5.How do you factor my smoking history and blood pressure into the decision, since they aren't directly calculated in the PHASES score?

Questions For You

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References

References (16)
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This page explains brain aneurysm risk scores for informational purposes only and does not constitute medical advice. Discuss your imaging, health history, and follow-up or treatment plan with your clinician.

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