Modified Fisher scale
CT grade of subarachnoid haemorrhage — risk of symptomatic vasospasm
Sources last checked: 2026-10-13
Modified Fisher scale
CT grade of subarachnoid haemorrhage — risk of symptomatic vasospasm
The 2006 paper gave no measurement threshold for 'thick' versus 'thin' blood, so grading between 1/2 and 3/4 is partly subjective. Use the CT closest to ictus.
Interpretation
| Grade 0–1 | Reference group for vasospasm risk in the derivation study. |
|---|---|
| Grade 2 | Symptomatic vasospasm: crude OR 1.6 vs grade 0–1. |
| Grade 3 | Symptomatic vasospasm: crude OR 1.6 vs grade 0–1. |
| Grade 4 | Symptomatic vasospasm: crude OR 2.2 vs grade 0–1 — highest risk. |
What is the Modified Fisher scale?
The modified Fisher scale grades the amount and distribution of blood on the first CT after subarachnoid haemorrhage from 0 to 4, combining cisternal clot thickness with intraventricular haemorrhage. Frontera and colleagues developed it in 2006 from 1355 placebo-arm patients of the tirilazad trials, as a better predictor of symptomatic vasospasm than the original 1980 Fisher scale.
When to use it
- Estimating the risk of symptomatic vasospasm and delayed cerebral ischaemia after SAH.
- Describing the vasospasm risk that underlies neuromonitoring intensity (transcranial Doppler, clinical checks) in the first two weeks.
- Describing imaging severity in reports and studies.
When not to use it
- On CT obtained days after the bleed, when blood has redistributed or cleared.
- For non-aneurysmal perimesencephalic haemorrhage, which has a much lower vasospasm risk.
- Confusing it with the original Fisher scale (grades 1–4), which uses different definitions.
How it is calculated
| Criterion | Points |
|---|---|
| Initial non-contrast CT | |
| 0 — No SAH, no IVH | 0 |
| 1 — Focal or diffuse thin SAH, no IVH | 1 |
| 2 — Focal or diffuse thin SAH, with IVH | 2 |
| 3 — Thick SAH, no IVH | 3 |
| 4 — Thick SAH, with IVH | 4 |
Clinical pearls and limitations
- The 2006 paper gave no measurement threshold for 'thick' versus 'thin' blood, so grading between 1/2 and 3/4 is partly subjective. Use the CT closest to ictus.
- Any intraventricular blood, however small, counts as IVH.
- 'Thick' means clot completely filling at least one cistern or fissure; there is no millimetre threshold in the original paper.
- Risk rises with grade, but even grade 1 does not exclude vasospasm.
Frequently asked questions
What is the difference between the Fisher and the modified Fisher scale?
The original 1980 scale used clot thickness measurements and paradoxically put thick IVH-only bleeding in grade 4; the modified scale combines thin/thick cisternal blood with presence of IVH and predicts vasospasm better.
Which grade carries the highest vasospasm risk?
Grade 4 (thick SAH with IVH): crude odds ratio about 2.2 compared with grades 0–1 in the derivation study.
Should I use the first CT?
Yes, the scale was defined on the initial non-contrast CT.
Evidence and guidelines
- Primary source: 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 computerized tomographic scanning. Neurosurgery 1980;6(1):1-9.
- Steiner T et al. European Stroke Organization guidelines for the management of intracranial aneurysms and subarachnoid haemorrhage. Cerebrovasc Dis 2013;35(2):93-112.
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