The PHASES score is a clinical tool used to estimate the 5-year risk of rupture for individuals with an intracranial aneurysm, based on specific patient characteristics. This involves entering data into six categories: population background, hypertension status, age, size of the aneurysm, history of prior subarachnoid hemorrhage from a different aneurysm, and the anatomical location of the aneurysm.

Here is how each category contributes to the scoring:

1. Population:
   - North American or European (excluding Finnish): 0 points
   - Japanese: 3 points
   - Finnish: 5 points

2. Hypertension:
   - No: 0 points
   - Yes: 1 point

3. Age:
   - Under 70 years: 0 points
   - 70 years and over: 1 point

4. Size of the Aneurysm:
   - Less than 7.0 mm: 0 points
   - 7.0 to 9.9 mm: 3 points
   - 10.0 to 19.9 mm: 6 points
   - 20 mm or larger: 10 points

5. Earlier Subarachnoid Hemorrhage from Another Aneurysm:
   - No: 0 points
   - Yes: 1 point

6. Site of the Aneurysm:
   - Internal carotid artery: 0 points
   - Middle cerebral artery: 2 points
   - Anterior cerebral or posterior communicating or posterior circulation: 4 points

The total score is the sum of the points from these categories, which then corresponds to a specific risk interpretation for aneurysm rupture over a 5-year period:

- 0 to 2 points: 5-year rupture risk is 0.4% (range: 0.1-1.5%)
- 3 points: 5-year rupture risk is 0.7% (range: 0.2-1.5%)
- 4 points: 5-year rupture risk is 0.9% (range: 0.3-2.0%)
- 5 points: 5-year rupture risk is 1.3% (range: 0.8-2.4%)
- 6 points: 5-year rupture risk is 1.7% (range: 1.1-2.7%)
- 7 points: 5-year rupture risk is 2.4% (range: 1.6-3.3%)
- 8 points: 5-year rupture risk is 3.2% (range: 2.3-4.4%)
- 9 points: 5-year rupture risk is 4.3% (range: 2.9-6.1%)
- 10 points: 5-year rupture risk is 5.3% (range: 3.5-8.0%)
- 11 points: 5-year rupture risk is 7.2% (range: 5.0-10.2%)
- 12 points or more: 5-year rupture risk is 17.8% (range: 15.2-20.7%)

By understanding each input's contribution to the score, medical professionals can gauge the relative risk, aiding in clinical decision-making regarding monitoring and intervention strategies.

The PHASES score is a clinical calculator used to estimate the 5-year risk of rupture for intracranial aneurysms. The acronym PHASES stands for Population, Hypertension, Age, Size of aneurysm, Earlier subarachnoid hemorrhage from another aneurysm, and Site of aneurysm. This scoring system is applicable to patients with unruptured intracranial aneurysms. 

The clinical utility of the PHASES score is to aid clinicians in decision-making regarding the management of unruptured intracranial aneurysms. It helps to stratify patients into different risk categories and thus guide treatment strategies, which can range from conservative management to surgical intervention.

The PHASES score may not be applicable to patients with ruptured aneurysms, fusiform aneurysms, or aneurysms associated with arteriovenous malformations. It is also less reliable in patients with multiple aneurysms or in those with a family history of aneurysmal subarachnoid hemorrhage.

PHASES score for intracranial aneurysm rupture risk