[Predictive quality of the injury severity score in the systematic use of cranial MRI]

Abstract

Aim: The ABBREVIATED INJURY SCORE (AIS) for the head is mostly coded on the basis of cranial computed tomography (CT). It defines, to a large extent, the predictive potency of the INJURY SEVERITY SCORE (ISS). The present study investigates whether the predictive capacity of the ISS can be improved by the systematic use of data from cranial MRI.

Method: 167 patients, who had been in a coma for at least 24 hours following trauma, underwent an MRI examination within 8 days. All had been found to have an intracranial injury on initial CT. 49 % had also suffered extracranial injuries. The GLASGOW OUTCOME SCALE (GOS) was determined 6 months post trauma. AIS, ISS and GOS values were rated as ordinal measurements. A contingency table was used as the statistical method of analysis, with a significance assumed as p < 0.05 (Chi (2) test).

Results: The median ISS based on CT was 16 and did not correlate with the GOS. 63 % of the patients revealed brain stem lesions on MRI. If these were coded with an AIS of 5, the median ISS increased significantly to 29. Thus, the correlation to the GOS was now significant. At ISS scores of 5-9, 18 % of the patients died; at scores of 50-54 the rate of favourable treatment outcomes still amounted to 50 %. Since it is now known that brain stem lesions can also have a favourable prognosis, the AIS coding was modified and adapted to the mortality of the singular types of lesion. Hence the median ISS again decreased to 16. The correlation to the GOS was significant, and the predictive potency of the ISS further improved. The prognostic potency of the REVISED INJURY SEVERITY CLASSIFICATION (RISC) score was improved by use of adapted MRI data.

Conclusion: If visible brain stem lesions on MRI were coded according to the AIS guidelines, there was a significant increase in the ISS which correlated significantly to the GOS. If the AIS coding was adjusted to the prognostic significance of individual brain stem lesions, there was a further improvement in the prognostic potency of the ISS. The study encourages the inclusion of data obtained from MRI diagnostics in the ISS calculation. There are alternative ways.