Introduction: Fisher grade is a computer tomography (CT) grade of subarachnoid hemorrhage (SAH) based on blood load on initial scan first proposed in 1980 [1]. This was shown to be well correlated with increasing risk of developing delayed ischaemic neurological deficit (DIND) for increasing grades 1-3 then not correlating with grade 4. On this basis, the modified Fisher grading system was proposed [2]. We aimed to validate these grading systems in our cohort of SAH.

Methods: Retrospective analysis was carried out on prospectively collected data for 609 consecutive patients referred to the West of Scotland regional neurosurgical service (population 2.7 million) with a diagnosis of SAH between August 2010 and August 2013. Each admission CT scan, for those patients accepted for investigation was independently graded for both Fisher and modified Fisher grades by two raters. Inter-rater agreement was calculated using Cohen’s kappa coefficient, and the rate of DIND assessed against increasing grade using the Chi square test.

Results: 609 patients with SAH were identified (61.9% were female). Average age at presentation was 54.8±13.5 (range 9-89 years). 526/609 (86.4%) were accepted for further investigation and treatment, the remainder refused on the grounds of fitness for intervention. Fisher grade had a high level of inter-rater agreement (Kappa=0.946±0.011;95% CI 0.924–0.968), and showed positive correlation at all grades for DIND (Fisher1: 4.9%, Fisher2: 12.3%, Fisher3: 14.9%, Fisher4: 32%), contrary to the published literature (P<0.00001). Modified Fisher grade (1-4) had a higher level of inter-rater agreement (Kappa=0.966±0.009; 95% CI 0.949–0.984), and also showed positive correlation at all grades for DIND (7.6%, 21.1%, 21.8%, 30% respectively, P=0.00003).

Conclusions: Both Fisher and Modified Fisher grading systems for assessement of blood load on initial CT scan are well correlated with risk of development of delayed ischaemic neurological deficit. However, the modified Fisher grading system has a higher index of inter-rater agreement.

Patient Care: This study allows clinicians to target patients at high risk of developing DIND.

Learning Objectives: Discussion of CT blood load grading systems and likelihood of development of DIND.

References: [1] Fisher CM, Kistler JP, Davis JM. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by computerized tomographic scanning. Neurosurgery. 1980 Jan;6(1):1-9. [2] Frontera JA, Claassen J, Schmidt JM, Wartenberg KE, Temes R, Connolly ES Jr, MacDonald RL, Mayer SA. Prediction of symptomatic vasospasm after subarachnoid hemorrhage: the modified fisher scale. Neurosurgery. 2006 Jul;59(1):21-7; discussion 21-7.