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.
🧮 Interactive Calculator
📐 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.