Subarachnoid Hemorrhage (SAH) is often treated as a uniform condition, but its prognosis and treatment strategy differ greatly depending on the cause of the bleeding. While ruptured unruptured aneurysms, often detected during brain checkups, account for over 80% of cases, Non-Aneurysmal Subarachnoid Hemorrhage (NA-SA), where no aneurysm is found, generally has a relatively favorable prognosis.
SAH is primarily classified by its cause, rather than the location or shape of the bleeding. This classification is the standard used in the guidelines of the Japan Neurosurgical Society.
Types of Subarachnoid Hemorrhage (By Cause) Current as of 2025
| Type | Frequency (Japan) | Main Age/Gender | Characteristics, Prognosis, and Treatment Key Points |
| 1. Ruptured Cerebral Aneurysm | 80–85% | Ages 40–70s, 2xmore common in women | Most frequent cause. Coiling or clipping is mandatory.Extremely high risk of re-bleeding (20–30% in the first 24 hours). |
| 2. Non-Aneurysmal SAH (NA-SA) | Approx. 10% | Ages 40–60s | No aneurysm is found. Bleeding is often localized to the central surface of the brain (interhemispheric fissure/interfrontal lobe). Prognosis is relatively good. |
| 3. Ruptured Arteriovenous Malformation (AVM) | 3–5% | Ages 20–40s, slightly more common in men | Common in younger individuals. May be accompanied by seizures. Treatment is a combination of surgery, radiation, and embolization. |
| 4. Associated with Moyamoya Disease | 1–2% | Children ∼ 30s, unique to the Japanese population | Bleeding occurs from Moyamoya vessels. Prone to concomitant cerebral infarction (ischemic stroke). |
| 5. Spinal Arteriovenous Malformation/Fistula | <1% | Ages 30–60s | Severe pain in the lower back or back → followed by headache. Caused by vessels in the spinal cord. |
| 6. Dissecting Cerebral Aneurysm | 1–2% | Ages 30–50s | Often vertebral artery dissection. Stent placement is becoming the dominant treatment over coiling. |
| 7. Brain Tumor / Hematologic Disorders, etc. | <1% | All ages | E.g., Leukemia, coagulation disorders, or related to anticoagulant use. |
Quick Comparison Table
| Type | Severity of Headache | Re-bleeding Risk | 30-Day Mortality Rate | Treatment Urgency | Preventable by Brain Checkup? |
| Aneurysmal Rupture | ★★★★★ | Extremely High | 35–40% | Highest Priority | ⨀ (Almost always detectable by MRA) |
| Non-Aneurysmal (NA-SA) | ★★★★☆ | Low | <10% | Moderately Urgent | ◯ (Some require observation) |
| AVM | ★★★★☆ | Moderate | 15–20% | Urgent | ⨀ |
| Moyamoya Disease | ★★★☆☆ | Moderate | Approx. 20% | Urgent | ⨀ |
Key Points Families Must Know
- Over 90% of SAH cases are caused by either a Cerebral Aneurysm or are Non-Aneurysmal.
- If an aneurysm is found, it is classified as an “Unruptured Cerebral Aneurysm” → Treatment with coiling or clipping before rupture can prevent SAH almost 100%.
- If the headache is the “worst you have ever experienced” plus vomiting (even once), suspect Aneurysmal Rupture as the highest priority (even if NA-SA, treatment is still necessary, but the prognosis is vastly different).
