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

It was modified from the original Fisher scale in 2006 ¹ to account for patients with thick cisternal blood and concomitant intraventricular hemorrhage. 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.

Usage

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.

Classification

• grade 0

  • no subarachnoid hemorrhage (SAH)

  • no intraventricular hemorrhage (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 hemorrhage.

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

Differences with the Fisher scale

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

See also

• Hunt and Hess grading system

• WFNS grading system

• cerebral vasospasm following subarachnoid hemorrhage