Extradural hematomas: measurement of size by volume summation on CT scanning.

The method of volume summation (V = T(A1 + A2 ... An) was used to measure the size of extradural hematomas. The accuracy was tested on six different artificial silicone hematomas and the mean difference was -2.7 ml, SD 3.7 ml. The reproducibility was tested on CT scans of clinical hematomas, SD was 2.1 ml. An empirical formula for volume estimation then found: 0.5 X height X length X depth was moderately reliable, while midline shift and "vesselfree space" were poor indicators of size. In conclusion, the volume summation with manual outlining was found to be highly accurate, but the problems of CT smoothing, spectral shift artifact, partial volume effect and separation of the hematoma from other structures must be considered.