Modified Fisher Scale Calculator – Subarachnoid Hemorrhage Vasospasm Risk

Clinical calculation support · Verify results before clinical use

CT Hemorrhage Assessment

Select the subarachnoid blood thickness and whether intraventricular hemorrhage is present on the admission CT.

—Grade

The combination of no visible SAH with IVH is not represented by the canonical Modified Fisher grades. Confirm the CT findings and interpret outside this calculator rather than assigning a grade.

0Modified Fisher

CT blood pattern

Grade 0 — No SAH or IVH

Lowest reference category for symptomatic vasospasm in the modified scale.

Clinical interpretationNo subarachnoid or intraventricular blood is selected. This scale is intended for patients with SAH; reassess the CT and clinical diagnosis.

This is a radiographic risk-stratification grade, not an individual probability of vasospasm or delayed cerebral ischemia. It does not replace neurological examination, clinical monitoring, vascular imaging, or specialist assessment.

About the Modified Fisher Scale

The Modified Fisher Scale is a CT-based grading system for subarachnoid hemorrhage that incorporates both the thickness of cisternal blood and the presence of intraventricular hemorrhage. It was developed to improve prediction of symptomatic vasospasm compared with the original Fisher scale.

Use the admission non-contrast head CT and assess the cisternal/fissural blood burden together with ventricular blood. The scale is most appropriately applied in the context of aneurysmal SAH; the CT pattern should be interpreted by a qualified clinician.

Grade definitions

Grade	Cisternal SAH	IVH
0	No visible SAH	Absent
1	Thin (<1 mm)	Absent
2	Thin (<1 mm)	Present
3	Thick (≥1 mm)	Absent
4	Thick (≥1 mm)	Present

Clinical use and limitations

Higher grades are associated with greater risk of symptomatic vasospasm at a population level.
The grade is not a stand-alone prediction of an individual patient's outcome and does not quantify a calibrated absolute risk.
It does not directly diagnose vasospasm or delayed cerebral ischemia.
Clinical severity, neurological status, aneurysm characteristics, treatment, and other patient factors also influence outcome.
Isolated IVH without visible cisternal SAH is not represented in the five canonical combinations above; do not force a grade.

Evidence & References

Claassen J, Bernardini GL, Kreiter K, et al.Effect of cisternal and ventricular blood on risk of delayed cerebral ischemia after subarachnoid hemorrhage: the Fisher scale revisited. Stroke. 2001;32(9):2012–2020. DOI: 10.1161/hs0901.095677.

Frontera JA, Claassen J, Schmidt JM, et al.Prediction of symptomatic vasospasm after subarachnoid hemorrhage: the modified fisher scale. Neurosurgery. 2006;59(1):21–27. DOI: 10.1227/01.neu.0000243277.86222.6c.

Hoh BL, Ko NU, Amin-Hanjani S, et al.2023 Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage: A Guideline From the American Heart Association/American Stroke Association. Stroke. 2023;54:e314–e370. DOI: 10.1161/STR.0000000000000436.

Clinical disclaimer: This calculator supports CT-based classification only. It is not a substitute for expert neuroradiological review or specialist care. Do not use the Modified Fisher grade alone to make treatment, monitoring, or prognostic decisions. The scale does not provide a patient-specific probability and should be considered alongside the full clinical picture.