ANALYSIS OF INTEROBSERVER DISAGREEMENT IN THE ASSESSMENT OF SUBARACHNOID BLOOD AND ACUTE HYDROCEPHALUS ON CT SCANS

The purpose of this study was to analyse factors for interobserver dis agreements in two scales used for the assessments of the amount of blo od in subarachnoid space (Fisher grading) and of acute hydrocephalus o n computerized tomographic (CTI scans. The assessments made by four ne uroradiologists on 59 CT scans obtained in the acute stage after subar achnoid hemorrhage were analysed by a statistical method by Svensson a nd Helm. This method permits the separation of the inter-observer disa greements in their random and systematic components. The overall consi stency of the assessments was significant (p < 0.0005) but the neurora diologists disagreed on half of the CT-scans. The kappa values were 0. 50-0.63. The analysis showed that the main reason for disagreements wa s systematic inter-observer differences in their use of the clinically most important parts of staging, i.e. subarachnoid clot or intraventr icular blood (Fisher grading) and too low categories (hydrocephalus). The main conclusion from this study is that the proper remedy for Fish er grading and for grading of hydrocephalus is a sharpening of the cri teria of specific category levels and given this improvement both grad ing systems will show a high level of reliability.