Modified Fisher scale
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 developed from the original Fisher scale which was modified to account for patients with thick cisternal blood and concomitant intraventricular (IVH) hemorrhage.
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 hemorrhage (SAH)
- no intraventricular hemorrhage (IVH)
- incidence of symptomatic vasospasm: 0%
- 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: the original study did not include a measurement of thick vs thin hemorrhage. Any IVH is counted
Differences with the Fisher scale
The main differences between the Fisher scale and modified Fisher scale are :
- 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
