Accurate measurement of defect skull area.

How to perform defective skull reconstruction and accurate measurement of defect skull area?

Using latest Slicer Preview Release, you can draw a closed curve on the skull using Markups module and compute the surface area as described here: How can I calculate an area on a CT image. I can calculate volumes (mm^3) but not areas (mm^2)

If this is not what you need then let us know. There are some other options, too.