Modified Fisher scale

Last revised by Rohit Sharma on 6 Mar 2024

The modified Fisher scale is a method for radiological grading subarachnoid haemorrhage (SAH) secondary to intracranial aneurysm rupture, assessed on the first non-contrast CT.

It was modified from the original Fisher scale to account for patients with thick cisternal blood and concomitant intraventricular haemorrhage. When using the modified Fisher scale, the risk of developing vasospasm progressively increases with each grade; in the original Fisher scale, the risk counterintuitively peaked at grade 3 and decreased for grade 4.

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, preferred by many, are still widely used. It is essential to note that the latter is more than a mere refinement of the original description; therefore, it is important to specify which scale is used 7.

  • grade 0

    • no subarachnoid haemorrhage (SAH)

    • no intraventricular haemorrhage (IVH)

    • incidence of symptomatic vasospasm: 0% 3

  • grade 1

    • focal or diffuse, thin SAH

    • no IVH

    • the incidence of symptomatic vasospasm: 24%

  • grade 2

    • focal or diffuse, thin SAH

    • IVH present

    • the incidence of symptomatic vasospasm: 33%

  • grade 3

    • thick SAH

    • no IVH

    • the incidence of symptomatic vasospasm: 33%

  • grade 4

    • thick SAH

    • IVH present

    • the incidence of symptomatic vasospasm: 40%

Note: the original study did not include a specified measurement or criteria to define thick vs thin haemorrhage.

Note: Any intraventricular haemorrhage, no matter how small, is counted.

The main differences between the Fisher scale and modified Fisher scale are 4,5:

  • in Fisher scale, no SAH is grade 1

    • grade 0 in modified Fisher scale

  • in Fisher scale, thin SAH with 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 the presence of SAH

    • in modified Fisher scale it is either grade 2 if thin or no SAH, or grade 4 if thick SAH

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