Fisher Grade Calculator

The Fisher grade classifies the pattern of blood seen on the initial non-contrast head CT after aneurysmal subarachnoid hemorrhage, for the specific purpose of predicting cerebral vasospasm rather than describing overall severity of illness. The original four-grade scale keys on the thickness and distribution of subarachnoid blood: grade 1 no visible blood, grade 2 a diffuse or vertical layer under 1 mm, grade 3 a localized clot or vertical layer of 1 mm or more, and grade 4 intracerebral or intraventricular clot with diffuse or absent subarachnoid blood. Grade 3 carries the highest vasospasm risk because the volume of blood adjacent to the basal arteries drives the process, as breakdown of erythrocytes releases oxyhemoglobin and free iron into the cisterns over several days, provoking arterial narrowing and inflammation. This produces the scale's well-known oddity: risk is not monotonic, since grade 4 can carry less vasospasm risk than grade 3 despite sounding more severe. The modified Fisher scale resolves this by grading on two axes, thin versus thick subarachnoid blood and the presence or absence of intraventricular hemorrhage, giving a risk that climbs steadily from roughly 5 to 15 percent at grade 1 to 40 percent or more at grade 4. Vasospasm and delayed cerebral ischemia typically appear between days 4 and 14, peaking around days 7 to 10, and affect a substantial minority of survivors of the initial bleed. Inter-rater agreement on thin versus thick blood is only moderate, and the original scale was calibrated on 1970s CT scanners far less sensitive than current equipment.

C. Miller Fisher, a Canadian-born neurologist at Massachusetts General Hospital better known for describing lacunar infarction and carotid territory disease, published the scale with J. P. Kistler and J. M. Davis in Neurosurgery in 1980. Computed tomography had been clinically available only since the early 1970s, and their contribution was to demonstrate that the amount and location of blood visible on this new modality predicted which patients would later develop symptomatic vasospasm. Before CT, subarachnoid hemorrhage was diagnosed by lumbar puncture and angiography, and there was no practical way to quantify the blood burden at presentation. The scale's limitations became apparent as scanner resolution improved and larger cohorts accumulated, particularly its non-linear relationship between grade and risk. In 2001 Jan Claassen and colleagues published an analysis in Stroke showing that cisternal and ventricular blood contributed independently to delayed cerebral ischemia, which formed the basis of the modified Fisher scale. Jennifer Frontera and colleagues validated the modified version against symptomatic vasospasm in Neurosurgery in 2006, and many neurocritical care units adopted it in preference to the original. The Fisher grade is used alongside clinical scales such as Hunt and Hess and the World Federation of Neurosurgical Societies grade, which measure neurological status rather than blood burden. Management has been anchored since the 1980s on oral nimodipine, the one drug with consistent outcome benefit after aneurysmal subarachnoid hemorrhage.