Segmentation method for cerebrspinal fluid space

I am a new 3D slicer user. I am looking to build a 3D model of the cerebrospinal fluid space from CT images of the human brain. I was wondering if someone could elaborate on how I should go about it. I tried using thresholding in the editor module as they have a predefined scale for CSF space, but that didn’t quite work out.
Any help would be great!

What was the problem?

In general, if there is intensity difference between regions that you would like to separate, “Grow from seeds” effect works very well. You would paint a few strokes (“seeds”) with the Paint effect inside CSF using one segment, and outside using another segment. Then, “Grow from seeds” effect should be able to create a complete CSF segmentation. If the results are not perfect then you can interactively edit the seeds. Check out these tutorials to learn how to use Grow from seeds and other effects.