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Fisher Grading Scale for Subarachnoid Hemorrhage (SAH)
Fisher Grading Scale for Subarachnoid Hemorrhage (SAH)
CT appearance
ResultFisher grade 1
No or diffuse thin cisternal blood – severe vasospasm was rare in the original series (severe spasm developed in only 1 of 18 such cases).
When to use
- Estimating the risk of angiographic and symptomatic vasospasm after aneurysmal subarachnoid hemorrhage from the initial non-contrast CT.
Formula
Grade assigned from a single non-contrast head CT based on the amount and pattern of subarachnoid and intraventricular/intraparenchymal blood (grades 1-4 as above); grade is not additive.
Pearls and pitfalls
- Largely superseded in clinical use by the modified Fisher scale, which separately accounts for intraventricular hemorrhage and better stratifies vasospasm risk.
- Grade 4 is a recognized weak point of the original scale: despite the presence of blood, it did not show a clean, reproducible step-up in vasospasm risk over Grades 1-2, unlike the clear signal seen with Grade 3. Prefer the Modified Fisher scale when precise risk stratification is needed.