Modified Fisher scale

The modified Fisher scale is a method for grading subarachnoid haemorrhage (SAH) secondary to intracranial aneurysm rupture, seen on non-contrast CT. It was developed from the original Fisher scale which was modified to account for patients with thick cisternal blood and concomitant intraventricular (IVH) or intraparenchymal haemorrhage.

Moreover, the risk of developing vasospasm progressively increases with each grade of the modified Fisher scale. Whereas the risk was highest for grade 3 and then decreased for grade 4 while using the original Fisher scale.

Classification

• 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
  • thin focal or diffuse SAH
  • IVH present
  • the incidence of symptomatic vasospasm: 33%
• grade 3
  • thick focal or diffuse SAH
  • no IVH
  • the incidence of symptomatic vasospasm: 33%
• grade 4
  • thick focal or diffuse SAH
  • IVH present
  • the incidence of symptomatic vasospasm: 40%

Note: thin SAH is <1 mm thick and thick SAH is >1 mm in depth

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 haemorrhage