A CT scan can get a pretty detailed look at
ovarian cysts so your doctor saying it is not cancer has a fairly high degree of accuracy. Some traits they use to gauge malignancy potential are thickness of the walls, number of septations, papillary projections, solid matter versus fluid, pelvic ascites. Of course, the tissue will still need to be biopsied to be sure.
MOST ovarian cysts, including complex ones, are benign.