This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
After a ruptured brain aneurysm, blood spreads in the subarachnoid space around the brain. The amount of blood on the first CT scan predicts vasospasm, the narrowing of brain arteries that usually starts 3 to 14 days later and can cause delayed cerebral ischemia. Fisher, Kistler and Davis proposed the first grading in 1980; Jennifer Frontera and colleagues published the modified Fisher scale in 2006 to separate the effect of thick blood from the effect of blood in the ventricles.
The modified Fisher grades
| Grade | CT finding | Symptomatic vasospasm in the original series |
|---|---|---|
| 0 | No subarachnoid or ventricular blood | — |
| 1 | Thin subarachnoid blood, focal or diffuse, no ventricular blood | 24% |
| 2 | Thin subarachnoid blood with blood in both lateral ventricles | 33% |
| 3 | Thick subarachnoid clot, no ventricular blood | 33% |
| 4 | Thick subarachnoid clot with blood in both lateral ventricles | 40% |
A thick clot fills a cistern or a fissure completely; a thin layer does not. Ventricular blood means blood in both lateral ventricles. When the CT shows ventricular blood with no visible subarachnoid blood, the calculator counts it as grade 2.
The original Fisher scale
The calculator also gives the 1980 grade:
- No blood detected.
- Diffuse thin layer, under 1 mm thick.
- Localized clot or a layer 1 mm or thicker.
- Clot in the brain or the ventricles, with diffuse or no subarachnoid blood.
In the original scale grade 4 had a lower risk than grade 3, which was confusing; the modified version makes the risk rise steadily from 1 to 4.
How it is used
- Together with the clinical grades (Hunt and Hess, WFNS), it describes the bleed on admission.
- High grades lead teams to watch more closely for vasospasm, often with transcranial Doppler and repeated neurological exams in the intensive care unit.
- It is a common stratification variable in research on subarachnoid hemorrhage.
Limits
The grade depends on the timing of the scan, because blood clears over days, and on the reader. The percentages come from one hospital cohort and serve as orders of magnitude. Vasospasm can occur at any grade, so close monitoring follows every aneurysmal bleed, whatever its score.