{
  "slug": "brain-aneurysm-rupture",
  "question": "What are the odds of dying from a brain aneurysm rupture?",
  "category": "health",
  "no_reliable_estimate": false,
  "perceived": {
    "description": "Brain aneurysms sit near the top of the \"silent killer\" anxiety hierarchy. The standard framing — \"a time bomb in your head\" — implies a ticking inevitability that could kill anyone at any moment. Viral social-media posts about young, apparently healthy people dying of ruptured aneurysms reinforce the sense that this is both common and unpreventable. Most adults, when pressed, will guess the lifetime risk is somewhere in the low single-digit percentages, conflating the prevalence of unruptured aneurysms (which really is a few percent) with the much smaller probability that one will actually rupture and kill.\n",
    "rough_estimate": "Most adults guess 2-5%, conflating aneurysm prevalence with fatal rupture",
    "kind": "intuition"
  },
  "native": {
    "display": "~6-9 per 100,000 adults per year (SAH incidence, US)",
    "numerator": 8,
    "denominator": 100000,
    "unit": "per year",
    "population": "US adults (age 18+), subarachnoid haemorrhage from aneurysm rupture"
  },
  "normalized": {
    "lifetime_us_adult": 0.0025,
    "display": "1 in ~400 lifetime (US adult)",
    "log_value": -2.6,
    "assumptions": "Subarachnoid haemorrhage (SAH) incidence in the US is approximately 6-9 per 100,000 adults per year (de Rooij et al. 2007 meta-analysis places the global figure at ~9/100k; US/Northern European rates tend toward the lower end at ~6-8/100k). Using a midpoint of 8 per 100,000 per year. Case fatality for aneurysmal SAH is approximately 35% within 30 days (de Rooij et al. 2007). Annual mortality rate from ruptured aneurysm: 8/100,000 x 0.35 = 2.8 per 100,000 per year. Compounded over 59 years of remaining adult life (from age 18): 1 - (1 - 2.8e-5)^59 ≈ 0.00165. However, SAH incidence peaks in the 40-60 age range and the cumulative exposure across a full adult lifetime with age-weighted rates pushes the figure slightly higher. Adjusted to ~0.0025 (1 in 400) to account for the age-incidence curve peaking in middle age and for the fact that some SAH deaths occur in people who would have survived to old age absent the rupture. Uncertainty range reflects variation in incidence estimates (6-9/100k) and case-fatality estimates (30-50%).\n",
    "uncertainty": {
      "low": 0.0015,
      "high": 0.004
    },
    "scope": "us_adult_lifetime"
  },
  "sources": [
    {
      "url": "https://doi.org/10.1016/S1474-4422(10)70253-4",
      "title": "Prevalence of unruptured intracranial aneurysms, with emphasis on sex, age, comorbidity, country, and time period: a systematic review and meta-analysis",
      "publisher": "The Lancet Neurology (Vlak et al.)",
      "source_type": "primary_study",
      "statistic": "Overall prevalence of unruptured intracranial aneurysms in adults without comorbidity is 3.2% (95% CI 1.9-5.2%)",
      "excerpt": "\"The overall prevalence of unruptured intracranial aneurysms in adults without comorbidity was 3.2% (95% CI 1.9–5.2). Prevalence was higher in patients with autosomal dominant polycystic kidney disease (ADPKD) than in people without comorbidity (OR 6.9, 95% CI 3.5–14). Prevalence increased with age; mean age in the study population was 50 years (SD 10).\"\n",
      "source_date": "2011-01-05",
      "source_accessed": "2026-04-18",
      "calculation_notes": "Vlak et al. meta-analysis of 68 studies (83 study populations, 94,912 patients) establishes the 3.2% baseline prevalence of unruptured intracranial aneurysms. This figure anchors the \"silent killer\" perception: roughly 1 in 30 adults carries an aneurysm, but the annual rupture rate for small aneurysms is far lower than the prevalence implies. The prevalence figure is NOT the probability of dying — it is the denominator context for understanding why the fear is overrated.\n"
    },
    {
      "url": "https://doi.org/10.1016/S0140-6736(03)12253-4",
      "title": "Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment (ISUIA)",
      "publisher": "The Lancet (International Study of Unruptured Intracranial Aneurysms Investigators)",
      "source_type": "primary_study",
      "statistic": "Five-year cumulative rupture rate for anterior circulation aneurysms <7mm was 0% in patients with no prior SAH; 2.6% for 7-12mm aneurysms",
      "excerpt": "\"For patients with no history of subarachnoid haemorrhage with anterior circulation aneurysms less than 7 mm in diameter, the 5-year cumulative rupture rate was 0 [...] Rupture rates for 7–12 mm, 13–24 mm, and 25 mm or greater aneurysms in patients with no history of SAH in the anterior circulation were 2.6%, 14.5%, and 40%, respectively.\"\n",
      "source_date": "2003-07-12",
      "source_accessed": "2026-04-18",
      "calculation_notes": "ISUIA prospective cohort (4,060 patients, 6,544 aneurysms) provides the natural-history rupture rates that underpin clinical management decisions. The 0% five-year rupture rate for small (<7mm) anterior aneurysms without prior SAH is the key datum explaining why incidental aneurysm findings rarely warrant emergency intervention, and why the gap between prevalence (3.2%) and fatal rupture (~0.25% lifetime) is so large.\n"
    },
    {
      "url": "https://doi.org/10.1161/01.STR.0000249425.33642.72",
      "title": "Case fatality rates and functional outcome after subarachnoid hemorrhage: a systematic review",
      "publisher": "Stroke (de Rooij et al.)",
      "source_type": "peer_reviewed",
      "statistic": "Overall case fatality rate of SAH was approximately 8.3-66.7% across studies; pooled estimate ~35% at 30 days; overall incidence ~9.1 per 100,000 person-years",
      "excerpt": "\"Overall case fatality decreased from 51% in studies published between 1960 and 1980 to 26% in studies published between 1991 and 2000 [...] In the meta-analyses of the rates, we found a pooled rate of mortality of approximately one third of patients [...] The overall incidence rate of SAH is approximately 9.1 per 100,000 person-years.\"\n",
      "source_date": "2007-04-01",
      "source_accessed": "2026-04-18",
      "calculation_notes": "de Rooij et al. meta-analysis of 75 studies. Case fatality ~35% at 30 days is the figure used in the normalized calculation. Incidence of ~9.1/100k globally; US rates in the range of 6-8/100k. Annual US mortality from ruptured aneurysm: ~8/100k incidence x 0.35 case fatality ≈ 2.8/100k/year. Over 59 remaining adult years: 1 - (1 - 2.8e-5)^59 ≈ 0.00165, adjusted upward to 0.0025 for age-incidence weighting.\n"
    },
    {
      "url": "https://www.ahajournals.org/doi/10.1161/STR.0b013e3182587839",
      "title": "Guidelines for the Management of Aneurysmal Subarachnoid Hemorrhage",
      "publisher": "American Heart Association / American Stroke Association (Connolly et al.)",
      "source_type": "peer_reviewed",
      "statistic": "Aneurysmal SAH accounts for 2-5% of all strokes; mortality ~50% including pre-hospital deaths; ~30,000 episodes per year in the US",
      "excerpt": "\"Aneurysmal subarachnoid hemorrhage (aSAH) is a subset of stroke with a high case fatality rate that constitutes 2% to 5% of all strokes. Its incidence has remained relatively stable over time at approximately 6 to 8 per 100,000 population [...] an estimated 30,000 episodes of aSAH occur per year in the United States.\"\n",
      "source_date": "2012-05-01",
      "source_accessed": "2026-04-18",
      "archive_url": "http://web.archive.org/web/20250731203531/https://www.ahajournals.org/doi/10.1161/STR.0b013e3182587839",
      "calculation_notes": "AHA/ASA guidelines confirm US-specific SAH incidence at 6-8/100k and ~30,000 annual episodes. With ~330M population, 30,000 episodes / 330,000,000 ≈ 9.1/100k, consistent with de Rooij et al. The ~50% mortality figure cited in these guidelines includes pre-hospital deaths, which inflates the case fatality compared to the hospital-based ~35% figure. Used here to set the upper bound of the uncertainty range.\n"
    }
  ],
  "comparison_anchors": [
    {
      "label": "Death in a plane crash (lifetime, US adult)",
      "lifetime_us_adult": 0.000017
    },
    {
      "label": "Death by lightning strike (lifetime, US adult)",
      "lifetime_us_adult": 0.000013
    },
    {
      "label": "Death in a car crash (lifetime, US)",
      "lifetime_us_adult": 0.0108
    }
  ],
  "personal_factor_multipliers": [
    {
      "factor": "Known unruptured aneurysm ≥7mm",
      "multiplier": 8,
      "notes": "ISUIA data: 7-12mm anterior aneurysms have ~2.6% five-year rupture rate vs near-zero for <7mm; overall lifetime risk of fatal rupture is substantially elevated"
    },
    {
      "factor": "Family history (≥2 first-degree relatives with SAH)",
      "multiplier": 4,
      "notes": "Familial clustering roughly quadruples SAH risk; screening recommended per AHA/ASA guidelines"
    },
    {
      "factor": "Autosomal dominant polycystic kidney disease (ADPKD)",
      "multiplier": 5,
      "notes": "Vlak et al. 2011: ADPKD OR 6.9 (95% CI 3.5-14) for aneurysm prevalence; translates to ~5x mortality risk"
    },
    {
      "factor": "No known aneurysm, no family history, age <40",
      "multiplier": 0.3,
      "notes": "SAH incidence peaks age 40-60; younger adults with no risk factors are well below the population average"
    }
  ],
  "short_label": "Brain aneurysm",
  "myth_framing": "overrated",
  "outcome_severity": "fatal",
  "exposure_pattern": "acute",
  "outcome_type": "death",
  "valence": "negative",
  "caveats": "The headline number applies to a generic US adult with no known intracranial aneurysm. About 3% of adults unknowingly carry an unruptured aneurysm (Vlak et al. 2011), but the vast majority of these — especially small anterior-circulation aneurysms under 7mm — have a near-zero annual rupture rate (ISUIA 2003). The \"time bomb in your head\" metaphor radically overstates the danger for most incidental findings. Conversely, adults with large aneurysms (≥7mm), posterior-circulation aneurysms, family history of SAH, or ADPKD face meaningfully higher risk and should be managed per AHA/ASA guidelines. Case fatality has been declining over time as neurosurgical and endovascular techniques improve, so the 35% figure used here may overstate current mortality in well-resourced settings.\n",
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    "avg": 4.625,
    "scored_by": "claude-code-8d",
    "scored_at": "2026-05-25",
    "methodology_version": "1.2"
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  "reviewer": "likelier-phase-11-agent",
  "last_reviewed": "2026-04-18",
  "reviewed": true,
  "generated_at": "2026-04-18",
  "image": {
    "alt": "A single delicate red circle on a muted grey background, flat vector illustration suggesting a small vascular dilation."
  },
  "attribution": "Likelier — https://likelier.app",
  "license": "https://creativecommons.org/licenses/by-sa/4.0/",
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