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Fisher Scale — SAH Vasospasm Risk
CT-based grading of subarachnoid haemorrhage to predict cerebral vasospasm risk
Original Fisher
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Modified Fisher
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Vasospasm Risk: —
Management Implications: —
Original Fisher Scale
| Grade | CT Findings | Vasospasm Risk |
|---|---|---|
| 1 | No blood detected | Low (21%) |
| 2 | Diffuse thin SAH <1mm; no clots | Moderate (25%) |
| 3 | Localised clot or vertical layer ≥1mm | Highest (37%) |
| 4 | Diffuse/no SAH; intracerebral or IVH clots | Moderate (31%) |
Modified Fisher Scale
| Grade | CT Findings | Symptomatic Vasospasm |
|---|---|---|
| 0 | No SAH or IVH | 0% |
| 1 | Thin SAH, no IVH | 6% |
| 2 | Thin SAH with IVH | 14% |
| 3 | Thick SAH, no IVH | 33% |
| 4 | Thick SAH with IVH | 40% — highest risk |
Thick SAH defined as >1mm on CT
Modified Fisher preferred clinically — better predicts symptomatic vasospasm
Vasospasm typically occurs day 4–14 post-SAH
Modified Fisher preferred clinically — better predicts symptomatic vasospasm
Vasospasm typically occurs day 4–14 post-SAH
Management: All SAH grades: nimodipine 60mg PO q4h × 21 days (class I evidence). High-grade modified Fisher (3–4): intensive TCD monitoring, consider prophylactic hypertensive therapy. Vasospasm treatment: 3H therapy or endovascular intervention.
For clinical decision support only. Not a substitute for professional medical judgment.
