Modified Fisher Scale Calculator

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating stroke subtype caused by rupture of an intracranial aneurysm. Blood spreads into the subarachnoid space, and a serious delayed complication is cerebral vasospasm, which occurs 4-14 days after rupture and causes ischemic stroke in up to 30% of SAH patients.

The Modified Fisher Scale grades the appearance of blood on the initial CT scan and predicts vasospasm risk. It was developed from the original Fisher scale (1980), which had poor inter-rater reliability and inconsistency between grades 2 and 3. The modified version provides cleaner categories.

Grade 0: No SAH and no IVH. Vasospasm risk approximately 0%. Grade 1: Thin SAH, no IVH. Vasospasm risk approximately 12-24%. Grade 2: Thin SAH with IVH. Vasospasm risk approximately 21-33%. Grade 3: Thick SAH, no IVH. Vasospasm risk approximately 19-33%. Grade 4: Thick SAH with IVH. Vasospasm risk approximately 40%.

Thick blood is defined as >= 1 mm in any basal cistern or Sylvian fissure. IVH (intraventricular hemorrhage) independently increases vasospasm risk and reflects more severe hemorrhage.

After aneurysmal SAH, management includes:

• Securing the aneurysm (surgical clipping or endovascular coiling) to prevent rebleeding
• Nimodipine (a calcium channel blocker) for all SAH patients, regardless of grade, reduces delayed ischemia
• Transcranial Doppler ultrasonography to monitor for vasospasm
• Prophylactic hypervolemia is no longer routine; euvolemia is the current standard
• If symptomatic vasospasm occurs, induced hypertension and endovascular intervention are options

This calculator is a reference tool. Radiology interpretation and clinical context determine the actual grade.