Grading Systems for SAH
Many SAH grading systems have been created to help grade severity and to assist in prognostication.
We will focus on two systems.
- Modified Fisher Scale
- World Federation of Neurosurgical Societies (WFNS) scale
Modified Fisher Scale
The Modified Fisher Scale is a radiological grading system which uses CT findings to determine the risk of cerebral vasospasm. There are five grades (0-4) which are outlined below:
Basically a normal CTB
No subarachnoid haemorrhage
AND
No intra-ventricular haemorrhage
0% incidence of DCI
Focal or diffuse subarachnoid haemorrhage
AND
No intraventricular haemorrhage
24% incidence of DCI
Focal or diffuse subarachnoid haemorrhage
AND
Intraventricular haemorrhage present
33% incidence of DCI
Thick focal or diffuse subarachnoid haemorrhage
AND
No intraventricular haemorrhage
33% incidence of DCI
WFNS Grading System
The WFNS is a clinical grading system based on the glascow coma scale (GCS) score and neurological deficit observed. There are five grades (1-5) which we will explore below:
It makes more sense to perform the WFNS grading after neurological resuscitation, i.e. after inserting an EVD for hydrocephalus or after surgery for clot evacuation if this is warranted. This paper showed better correlation with outcomes if you wait until 12h post this “neurological resuscitation”.
Pros & Cons of these Systems
WFNS grading system
Advantages
- Fast and easy to calculate as GCS and neuro exam usually documented in all patients
- Does not require imaging
- High inter-observer reliability (not as high as MFS)
- Well validated prognostic tool for overall outcome
- There is a step-wise increase in the likelihood of a poor outcome with increasing grade
Disadvantages / Potential issues
- Relies on an accurate application of the GCS (however, as it compresses the GCS into 5 grades there is increased interobserver reliability)
- Significant increase in likelihood for a poor outcome in the step between grade 2 and 3
- By grouping patients with large differences in GCS (i.e. Grade 4 with a GCS range of 7-12) it is possible that patients in this group have widely different outcomes.
Modified Fisher Scale (MFS)
Advantages
- Unlike the original Fisher Scale it accounts for patients with thick cisternal blood and concomitant intraventricular (IVH) or intraparenchymal haemorrhage
- Risk of vasospasm increases with each grade of the MFS, whereas in the original Fischer Scale, risk peaked at grade 3, improving slightly in grade 4.
- Convenient as most patients receive a CT brain
- Very high intereliability
- Validated prognostic tool for radiological vasospasm
Disadvantages / Potential issues
- Doesn’t prognosticate for overall outcome well (predicts for radiological vasospasm)
- Clot density is not a strong feature of the system. Hence, a tiny amount of blood in the ventricles with receive the same score as a ventricle filled almost entirely with blood.
Other Grading Systems
Many (>40) have been created.
Early scales were very basic e.g. Bramwell, 1933 which categorised patients as “apoplectic vs. paralytic”
The Hunt and Hess Scale (1968) was the first to become widely adopted (described about 5 years prior to the Glasgow Coma Scale!)
Hunt & Hess Grading System
A measure of perioperative mortality risk, based on the intensity of meningeal inflammatory reaction, the severity of neurological deficit, the level of arousal, and the presence of associated disease. The Hunt and Hess Grading system remains one of the most widely recongised grading systems for SAH!
Asymptomatic or minimal headache and slight nuchal rigidity
Moderate to severe headache, cranial nerve palsies, nuchal rigidity but no other neurological deficits
Drowsy, confused or mild focal deficit
Stupour, moderate-to-severe hemiparesis, early decerebrate rigidity and “vegetative disturbance”
Deep coma, decerebrate rigidity, “moribund appearance”.
Ambiguous terms: “vegetative disturbance” and “moribund appearance”. This is acknowledged by the authors themselves in their introduction: “It is recognized that such classifications are arbitrary and that the margins between categories may be ill defined”.
In 1988, due to lack of data on the significance of features such as headache, nuchal rigidity, and major focal neurologic deficit, the WFNS Committee published the Universal SAH Grading Scale as above.
There have been several attempts to improve the discriminating potential of grading scales by increasing the granularity with which a patient’s condition is assessed.
Factors such as age, degree of intra-ventricular haemorrhage, hydrocephalus, cardiac dysfunction, and other medical co-morbidities may affect outcome.
In 1998 Ogilvy and Carter proposed a comprehensive grading system for patients with SAH that includes age, aneurysm size, Fisher grade, and Hunt and Hess score. However the Fisher scale has been superseded by the Modified Fisher and Hunt and Hess replaced by the WFNS scale, making this scale impractical to perform.
The 2014 SAH prognosis score (S = clinical status, A = age, and H = health conditions) is another scale proposed to better stratify patients by taking into account several important contributors to outcome. This includes GCS score, age, and medical co-morbidities, was also found to have better predictive power for mortality than the WFNS system.
In 2019, the SAFIRE grading system was published, which uses size of the aneurysm, age, Fisher grade and WFNS after resuscitation to predict functional outcomes at 2 months. Whether this system will be adopted remains to be seen.
With more recent developments in our understanding of Early Brain Injury (EBI) following aSAH, a new approach looking at the extent of cerebral oedema as a marker of EBI, the SEBES score, shows promise in predicting DCI and functional outcome following aSAH.
Our 47 year old patient, Katherine, deteriorated in the Emergency Department.
When examined, she would only open her eyes to a painful stimulus, was groaning and making incomprehensible sounds. She was still localising to a central painful stimulus.
Here is her CT scan:
What is her WFNS grade?
What is her Modified Fisher Grade?
What else does the CT show?
Have a look at this scan – slide up & down to scroll through.
What’s the modified fisher grade here?
What else can you see?
The CT demonstrates diffuse, thick subarachnoid haemorrhage throughout all basal cisterns, the cerebral convexities, bilateral sylvian fissures and interhemispheric fissures. There is also a very small subdural haematoma – be careful to not be distracted by the obvious findings and work through the entire scan!
There is blood in the lateral ventricles too – look for the layering.
Therefore the Modified Fisher Grade is 4 again.
[Scroll through the same CT below which has now been labelled for you!]