Fisher Grade (Original, Subarachnoid Hemorrhage CT)
The ORIGINAL FISHER GRADE (Fisher, Kistler and Davis 1980) grades the appearance of blood on the computed tomogram after subarachnoid hemorrhage.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Intracerebral or intraventricular blood
- No
- Subarachnoid blood on CT
- Localized clot, or a vertical layer ${M.THICKNESS_THRESHOLD_MM} mm…
Result: Fisher grade 3
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Grade 1
- No subarachnoid blood detected.
- Grade 2
- Diffuse or vertical layer of subarachnoid blood less than 1 mm thick.
- Grade 3
- Localized clot, or a vertical layer 1 mm thick or more. THE HIGHEST VASOSPASM RISK ON THE SCALE.
- Grade 4
- Intracerebral or intraventricular blood with diffuse or NO subarachnoid blood. Defined by LOCATION, not amount.
- NOT ordinal
- Risk rises 1 to 3 and grade 4 does NOT continue the trend. A higher grade does NOT mean higher vasospasm risk.
- Why
- Grade 4 changes what is measured - different blood in a different compartment. A speck of IVH with no SAH is grade 4.
- The flaw
- The same grade 4 covers a speck and a ventricle full of clot. That is why the modified scale was proposed.
- No mapping
- The modified scale adds a GRADE 0 and splits thickness from IVH into two axes. A Fisher 3 is NOT a modified Fisher 3.
- CT era
- The 1 mm threshold was measured on 1980-era CT. A modern scanner is not the same observation.
- Scope
- Grades a SCAN, not clinical severity (Hunt-Hess, WFNS). A low grade is NOT a reason to relax vasospasm monitoring.
What you enter
- Intracerebral or intraventricular blood.
- Subarachnoid blood on CT: none; thin (a diffuse or vertical layer less than 1 mm thick, grade 2); or thick-or-localized-clot (a localized clot or a vertical layer 1 mm or more, grade 3 - the HIGHEST vasospasm risk on the scale).
Full field descriptions
- Intracerebral or intraventricular blood. THIS DECIDES GRADE 4 BY COMPARTMENT, regardless of how much subarachnoid blood there is - and grade 4 is NOT the highest vasospasm risk.
How this is calculated
Fisher CM, Kistler JP, Davis JM. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by computerized tomographic scanning. Neurosurgery. 1980;6(1):1-9. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.