Fisher Grading Scale for Subarachnoid Hemorrhage (SAH)
Rates risk of vasospasm in aSAH based on amount and distribution of blood on CT.
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INSTRUCTIONS
This scale only applies to aneurysmal subarachnoid hemorrhage (aSAH). We recommend using the Modified Fisher Grading Scale based on more recent studies.
Clinician must be able to identify subarachnoid hemorrhage (SAH) and major neuroanatomical landmarks on head CT.
When to Use
Pearls/Pitfalls
Why Use
Patients with aSAH.
- The Fisher Grading Scale was originally designed to predict risk of cerebral arterial vasospasm in patients with aneurysmal subarachnoid hemorrhage (aSAH) based on radiographic distribution of subarachnoid hemorrhage.
- The Fisher scale is entirely radiographic and typically determined at presentation.
- Variable rates of vasospasm corresponding to each Fisher grade have been reported in studies; therefore, the scale should not be used to quote an exact probability of vasospasm or delayed cerebral ischemia (DCI).
- The Fisher scale should also NOT be used as the sole clinical data point to make decisions on medical management or goals of care.
Points to Keep in Mind:
- The Fisher scale has a number of shortcomings:
- It does not consider the effect of thick cisternal subarachnoid blood or intraventricular hemorrhage (IVH), which are both known risk factors for vasospasm (Claassen et al 2001, Wilson et al 2012). For this reason, the Modified Fisher Grading Scale is often preferred by many neurocritical care providers.
- Higher Fisher scale grades do not necessarily correlate with increasing probability of vasospasm. Studies show little to no difference between grades 1 and 2 (Claassen 2001), and that grade 4 is associated with a lower rate of clinical vasospasm than grade 3 (Fisher 1980 & 1983, Smith 2005, Frontera 2006, Kramer 2008).
- The original Fisher scale was developed based on measurements on paper printouts from a low-resolution EMI CT scanner, which was not reflective of true SAH thickness. In reality, most SAH is >1 mm thick, so Grades 1 and 2 are rare. (Rosen 2005)
- The scale does NOT apply to SAH due to trauma, arteriovenous malformations, cavernous angiomas, dural arteriovenous fistulae, cortical or sinus venous thromboses, mycotic aneurysms, or septic emboli with hemorrhagic transformation.
- Angiographic vasospasm occurs in at least 50% of patients with aSAH and often results in DCI, which occurs in up to 46% of all patients with aSAH and can cause devastating neurological consequences and/or death (Claassen 2001).
- Because vasospasm typically occurs between 4 and 14 days (“vasospasm window”) after the onset of aSAH, the Fisher scale may allow timely preventative treatment for vasospasm and DCI to be initiated (Fisher 1983).
- Despite its well-documented shortcomings, the Fisher grading scale remains widely used and well-known in critical care and neurocritical care communities.
No SAH detected
Diffuse or vertical layer of subarachnoid blood < 1mm thick
Localized clot and/or vertical layer within the subarachnoid space > 1mm thick
Intracerebral hemorrhage (ICH) or intraventricular hemorrhage (IVH) with diffuse or no SAH
Result:
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Next Steps
Evidence
Creator Insights
Advice
- Immediate neurological and neurosurgical consultation should be obtained for patients with evidence of any SAH on imaging or lumbar puncture, even if the SAH is likely to be non-aneurysmal in nature.
- Computed tomographic angiography (CTA) of the head is helpful to determine the presence of a lesion suitable for surgical or endovascular intervention.
- The need for obtaining cerebrovascular imaging, such as CTA of the head or catheter angiography, should be discussed with a neurological or neurosurgical consultant first.
- Similarly, the decision to start medications that have been shown to alter outcomes in aSAH (such as nimodipine and/or aminocaproic acid) should be deferred to the neurological or neurosurgical consultant.
Formula
Selection of appropriate criteria.
Facts & Figures
Score interpretation:
| Fisher grade | Blood on CT* | Risk of vasospasm |
|---|---|---|
| I | No SAH detected | Low (range 0-21%) |
| II | Diffuse or vertical layer of subarachnoid blood < 1mm thick | Low (range 0-25%) |
| III | Localized clot and/or vertical layer within the subarachnoid space > 1mm thick | Low to high (range 23-96%) |
| IV | ICH or IVH with diffuse or no SAH | Low to moderate (range 0-35%) |
*Measurements were made on printed EMI CT scans. The measurements were not scaled to the actual thickness.
Evidence Appraisal
- C. Miller Fisher’s seminal study of 47 patients with aSAH was a retrospective, single-center study that graded the amount/distribution of subarachnoid blood, and recorded the rate of angiographic and clinical vasospasm. While angiographic vasospasm was common, thick subarachnoid hemorrhage (greater than 1 mm thick) correlated with a high rate of clinical vasospasm (Fisher 1980).
- Rates of radiographic vasospasm (Fisher 1980):
- Grade 1: 36%
- Grade 2: 43%
- Grade 3: 100%
- Grade 4: 40%
- Rates of clinical vasospasm (Fisher 1980):
- Grade 1: 0%
- Grade 2: 0%
- Grade 3: 96%
- Grade 4: 0%
- Rates of radiographic vasospasm (Fisher 1980):
- A subsequent validation study of 41 patients confirmed that severe vasospasm (vasospasm causing a subjective change in neurological examination) occurred at a disproportionately higher rate in patients with Fisher grade 3 SAH (Kistler 1983).
- Rates of clinical vasospasm (Kistler 1983):
- Grade 1: 0%
- Grade 2: 14%
- Grade 3: 86%
- Grade 4: 0%
- Rates of clinical vasospasm (Kistler 1983):
- In a retrospective single-center study of 134 aSAH patients with modern CT scanners and rapid imaging, univariate and bivariate analyses showed that Fisher grade was not significantly associated with the development of symptomatic vasospasm (p=0.5). (Smith 2005)
- Rates of clinical vasospasm (Smith 2005)
- Grade 1: 0%
- Grade 2: 24%
- Grade 3: 28%
- Grade 4: 19%
- Rates of clinical vasospasm (Smith 2005)
- The largest vasospasm Fisher score study was a retrospective look at 1,335 patients from international placebo-controlled trials of aSAH. (Frontera 2006)
- Re-validation of the Fisher scale showed the following rates of clinical vasospasm:
- Grade 1: 21%
- Grade 2: 25% (OR not statistically significant)
- Grade 3: 37%
- Grade 4: 35% (OR trend towards statistically significant)
- In addition, multivariate analysis (adjusting for other clinical predictors of vasospasm) showed that an increase of 1 Fisher scale grade did not increase the risk of clinical vasospasm. (Frontera 2006)
- Re-validation of the Fisher scale showed the following rates of clinical vasospasm:
- A retrospective, single-center study of 237 patients with aSAH showed that Fisher 3 patients had significantly higher odds of clinical vasospasm and cerebral infarction than Fisher 1 or Fisher 2 patients (OR 6.9 and OR 14.3, respectively). Fisher 4 patients had higher, but not statistically significant, risks of all 3 outcomes. (Kramer 2008)
- Fisher grade 3, but not other Fisher grades, seems to be significantly associated with delayed ischemic complications of vasospasm.
- Rates of clinical vasospasm:
- Grade 1: 0%
- Grade 2: 7%
- Grade 3: 35%
- Grade 4: 12%
Non-vasospasm outcomes
- A retrospective single-center analysis of 292 patients with aSAH found that both Fisher and modified Fisher scales were significantly correlated with radiographic infarction, but an increase in Fisher scale grade had a higher odds ratio associated with infarction. (Woertgen 2003)
- A retrospective, single-center study showed that in comparison to patients without SAH, only patients with Fisher scale scores of 3 (RR 3.2) or 4 (RR 14.8) had increased risk of fair/poor outcome or death, whereas Fisher grade 1 and 2 patients did not (Ogilvy 1998).
- A retrospective analysis of 2,055 aSAH patients showed that surgical outcomes did not differ between Fisher grade 1 and 2 patients. (Osawa M 2001)
- In multivariate analysis from the same study, patients with Fisher grade >3 had poor surgical outcomes. (Osawa M 2001)
- A retrospective, single-center study of 237 patients with aSAH showed that Fisher 3 patients had significantly higher odds of poor neurological outcome than Fisher 1 or Fisher 2 patients (OR 11.9). This suggests that Fisher grade 3, but not other Fisher grades, may have prognostic value with respect to poor neurological outcome. (Kramer 1998)
Interobserver agreement
- A single-center study examining predictors of surgical outcome in aSAH showed that the Fisher scale had a high degree of interobserver agreement (k=0.9) (Ogilvy 1998).
- A retrospective single-center study analyzing 59 CT scans in SAH showed that the inter-observer agreement for the Fisher grading scale was moderate (k=0.63), mainly due to differences in determining IVH or subarachnoid clot. (Svensson 2005)
Literature
Original/Primary Reference
Fisher C, Kistler J, Davis J. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by computerized tomographic scanning. Neurosurgery. 1980;6(1):1-9.Validation
Kistler JP, Crowell RM, Davis KR, Heros R, Ojemann RG, Zervas T, Fisher CM. The relation of cerebral vasospasm to the extent and location of subarachnoid blood visualized by CT scan: a prospective study. Neurology. 1983; 33(4): 424-36.Smith ML, Abrahams JM, Chandela S, Smith MJ, Hurst RW, Le Roux PD. Subarachnoid hemorrhage on computed tomography scanning and the development of cerebral vasospasm: the Fisher grade revisited. Surg Neurol. 2005; 63:229-234; discussion 234-225.Frontera JA, Claassen J, Schmidt JM, Wartenberg KE, Temes R, Connolly ES, Loch Macdonald R, Mayer SA. Prediction of symptomatic vasospasm after subarachnoid haemorrhage: the modified Fisher scale. Neurosurgery. 2006; 58(7): 21-27.Kramer AH, Hehir M, Nathan B, Gress D, Dumont AS, Kassell NF, Bleck TP. A comparison of 3 radiographic scales for the prediction of delayed ischemia and prognosis following subarachnoid hemorrhage. Journal of Neurosurgery. 2008; 109:199-207Other References
Claassen J, Bernardini GL, Kreiter K, Bates J, Du YE, Copeland D, Connolly ES, Mayer SA. Effect of cisternal and ventricular blood on risk of delayed cerebral ischemia after subarachnoid hemorrhage: the Fisher scale revisited. Stroke. 2001; 32 (9): 2012-2020.Ogilvy CS, Carter BS. A Proposed Comprehensive Grading System to Predict Outcome for Surgical Management of Intracranial Aneurysms. Neurosurgery. 1998; 42(5): 959-968.Woertgen C, Ullrich OW, Rothoerl RD, Brawanski A. Comparison of the Claassen and Fisher CT classification scale to predict ischemia after aneurysmatic SAH? Central European Neurosurgery. 2003; 64(3):104-108.Svensson E, Starmark JE, Ekholm S, von Essen C, Johansson A. Analysis of interobserver disagreement in the assessment of subarachnoid blood and acute hydrocephalus on CT scans. Neurol Res. 1996; 18(6):487-494.Rosen DS, Macdonald RL. Subarachnoid Grading Scales: A Systematic Review. Neurocritical Care. 2005;2:110-118.Osawa M, et al. Results of direct surgery for aneurysmal subarachnoid haemorrhage: outcome of 2055 patients who underwent direct aneurysm surgery and profile of ruptured intracranial aneurysms. Acta Neurochir (Wien). 2001;143(7):655-63; discussion 663-4.
Dr. C. Miller Fisher
About the Creator
Charles Miller Fisher, MD, (d. 2014), was Professor Emeritus at Harvard Medical School, where he spent 50 years as a teacher and clinician. He was an active researcher in stroke neurology and is credited with identifying and naming transient ischemic attacks (TIA). He was a founder of the Massachusetts General Hospital Stroke Service and was inducted into the Canadian Medical Hall of Fame.
To view Dr. C. Miller Fisher's publications, visit PubMed
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