Fisher scale

Last revised by Frank Gaillard on 6 Mar 2024

The Fisher scale is the initial and best-known system of classifying the amount of subarachnoid hemorrhage on CT scans, described in 1980 4. Its primary use was in predicting the occurrence and severity of cerebral vasospasm, highest in grade 3 2,4

Although it is known as a scale, from grade 1 to grade 4, it should be noted that the risk of vasospasm only increases from grade 1 to 3, and is lower again in grade 4 2.

Numerous other scales have been proposed, incorporating various parameters, and aimed at predicting mortality, morbidity and/or vasospasm. 

Nonetheless, the Fisher scale and more recently the Modified Fisher scale are still widely used. It is important to note that the latter is more than a mere refinement of the original description and it is, therefore, essential to be explicit as to which scale is being used 6.

The modified Fisher scale is preferred by many over the original grading system, as the risk of symptomatic vasospasm in the original description was highest in grade 3 and lower in grade 4. 

  • grade 1

    • no subarachnoid (SAH) or intraventricular hemorrhage (IVH) detected

    • incidence of symptomatic vasospasm: 21% 3

  • grade 2

    • diffuse thin (<1 mm) SAH

    • no clots

    • incidence of symptomatic vasospasm: 25%

  • grade 3

    • localized clots and/or layers of blood >1 mm in thickness

    • no IVH

    • incidence of symptomatic vasospasm: 37%

  • grade 4

    • diffuse or no SAH

    • ICH or IVH present

    • incidence of symptomatic vasospasm: 31%

  • in Fisher scale no SAH is grade 1 (grade 0 in modified Fisher scale)

  • in Fisher scale thin SAH, no IVH is grade 2 (grade 1 in modified Fisher scale)

  • in Fisher scale thick SAH with no IVH is grade 3 (grade 3 in modified Fisher scale)

  • in Fisher scale any IVH is grade 4, irrespective of presence of SAH (in modified Fisher scale it is either grade 2 if thin or no SAH, or grade 4 if thick SAH) 4,5

ADVERTISEMENT: Supporters see fewer/no ads

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.