CT-based grading of subarachnoid haemorrhage to predict cerebral vasospasm risk
Original Fisher
—
—
Modified Fisher
—
—
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
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.
