a)    How are the World Federation of Neurosurgeons Score (WFNS) and the Fisher score calculated in the grading of aneurysmal subarachnoid haemorrhage (SAH)? (40% marks)

b)    What are the limitations of using these scores in the first 24 hours after the onset of SAH to    determine prognosis?    (60% marks)

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College answer

  • WFNS (clinical grade)
    • I – GCS 15, no motor deficit
    • II – GCS 13-14, no motor deficit
    • III – GCS 13-14 and motor deficit
    • IV – GCS 7-12 +/- motor deficit
    • V – GCS 3-6 +/- motor deficit
  • Fisher (radiological grade, based on brain CT)
    • I – no blood 
    • II – diffuse deposition of SAH without clots or layers of blood < 1mm
    • III – localized clots and /or vertical layers of blood 1 mm or more in thickness
    • IV – diffuse or no subarachnoid blood but intracerebral or intraventricular clots

WFNS is a clinically graded score – gives information on prognosis
WFNS 3+ worse outcome
Fisher gives information on vasospasm risk
Fisher 3+ higher risk of vasospasm

Limitations of grading systems:

Neither have high sensitivity or specificity for outcomes

The scores may alter depending on when they are calculated – initial presentation, on arrival to ED or on arrival ICU

Sedation or paralysis can confound the interpretation

Effects of hydrocephalus or seizure – may suggest an initially unfavourable outcome,

Effects of rebleed may confound an initial positive grade

Expert assessment is required for radiological interpretation WFNS uses GCS score which has poor inter-rater reliability 
 
Examiners Comments: 
 
Many candidates failed to address the specific limitations of the scores and instead described general issues effecting prognosis in subarachnoid haemorrhage. Several failed to mention both scoring systems. Overall there was poor knowledge of the scoring systems. 

 

Discussion

For answering this questions, no single reference is better than the 2005 review article by David Rosen.

a) In answer to the question "how are scores calculated", one may discuss the philosophy underlying the scoring system, or - more realistically - list the values used to calculate the scores. For reference and to simplify revision, links to the original articles are offered below, together with the grading system.

the WFNS scale:

  • Grade 1: GCS 15, no motor deficit.
  • Grade 2: GCS 13-14 without deficit
  • Grade 3: GCS 13-14 with focal neurological deficit
  • Grade 4: GCS 7-12, with or without deficit.
  • Grade 5: GCS <7 , with or without deficit.

the Fisher scale:

  • Grade 1 - no haemorrhage
  • Grade 2 - SAH less than 1mm thick, diffuse
  • Grade 3 - SAH more than 1mm thick, with localised clots
  • Grade 4 - intraventricular or parenchymal extension, with clots

b) 

Limitations of the Fisher score

  • It was developed when the imaging resolution was approximately 1\20th of what is currently available 
  • It may be difficult to apply for staff who are unfamiliar with CT imaging
  • It was validated in a small series of patients (by Kistler et al, 1981)
  • Grade 1 and 2 are very uncommon
  • Clot density and clot clearance rate are important factors which infuence the development of vasospasm, but which are not included in the scale. The same score (4) is given to the patient with a tiny speck of blood in the ventricle, as well as to the patient whose ventricles are full of thick clot. 
  • Unlikelty clinical scoring systsems, it does not correlate very well with clinical outcome- only with vasospasm

Limitations of the WFNS system

  • It relies on the accurate application of the GCS
  • It does not incorporate imaging data
  • It is unclear whether adding the additional focal neurodeficit dimension has any added benefit to the prognostic power of the scoring system (It may well be that admission GCS is the single best predictor of neurological outcome)
  • the expert committee behind the WFNS did not explain the reasoning behind the specific GCS breakpoints used for their definition
  • Grade 4, which represents a range of GCS scores between 7 and 12, includes a group of patients who may have widely different outcomes.
  • There is a significant step in the likelihood of poor outcome between Grade 2 and Grade 3 (0.61 vs 1.78)
  • There are very few Grade 3 patients in all studies of WFNS (usually, ~ 3%)

References

Drake, Charles G. "Report of World Federation of Neurological Surgeons Committee on a universal subarachnoid hemorrhage grading scale." J neurosurg 68 (1988): 985-986.

Fisher, C. M., J. P. Kistler, and J. M. Davis. "Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by computerized tomographic scanning." Neurosurgery 6.1 (1980): 1-9.

Rosen, David S., and R. Loch Macdonald. "Subarachnoid hemorrhage grading scales." Neurocritical care 2.2 (2005): 110-118.