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Neuroradiology
Demonstration data

Modified Fisher Scale

CT-based grading of subarachnoid haemorrhage that stratifies the risk of symptomatic vasospasm.

The modified Fisher scale grades aneurysmal subarachnoid haemorrhage on non-contrast CT using the thickness of cisternal/fissural blood and the presence of intraventricular haemorrhage (IVH), improving on the original Fisher scale by treating IVH as an independent risk factor.

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📐 Formula

Grade 0–4 from SAH thickness and presence of intraventricular haemorrhage

When to Use

  • Initial CT in aneurysmal subarachnoid haemorrhage.
  • Predicting the risk of symptomatic (delayed) cerebral vasospasm.
  • Risk-stratifying patients for monitoring intensity.

How It Works

  • Grade 0 — no SAH and no IVH.
  • Grade 1 — thin focal or diffuse SAH, no IVH.
  • Grade 2 — thin SAH with IVH.
  • Grade 3 — thick SAH, no IVH.
  • Grade 4 — thick SAH with IVH.

Interpreting the Result

  • Risk of symptomatic vasospasm rises with grade, from ~0% at grade 0 to ~30–40% at grade 4.
  • Thick cisternal blood and IVH each independently raise vasospasm risk.
  • Higher grades warrant closer neurological and transcranial Doppler surveillance.

Limitations & Pitfalls

  • Predicts vasospasm risk, not overall clinical severity (use Hunt–Hess or WFNS for that).
  • Inter-rater variability in judging "thin" versus "thick" blood.
  • Derived in aneurysmal SAH; not validated for traumatic SAH.

References

  • Frontera JA, Claassen J, Schmidt JM, et al. Prediction of symptomatic vasospasm after subarachnoid hemorrhage: the modified Fisher scale. Neurosurgery. 2006;59(1):21-27.
  • Fisher CM, Kistler JP, Davis JM. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by CT scanning. Neurosurgery. 1980;6(1):1-9.

⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.