sorta...the ct scan does 'slices' as it goes through your body in addition to a 'scout' scan that looks sorta like a regular x-ray but a little better. Using both the radiologists can determine what is going on. Obviouslly if you have a big mass on your ovary, pretty good chance it may be malignant. The radiologists can tell by certain measurements, experience, etc. if there is a good probability of it being a complex cyst or not.
Beyond that a CT scan is only one part of any good diagnosis/workup. Ultrasounds, MRI, PET, CA-125 tests, etc. all come into play to get an overall good picture for the oncologist.
Form the SimplyStar is right, only during surgery when the Gyn/Onc does the staging come into play. While they may have experience in determining if it is malignant, only during pathology at the lab is it actually determined.
My Doctor told me after a Ct scan that there was 99.9% chance that I had Ovarian cancer, as it was well advanced by then.... and Stage 4, so I guess they have a fair idea from the scan that it could be cancer, but maybe not in all cases.
No only surgery and a path report of the tissue removed can diagnose OVCA