Re: can a doctor look at a cat scan and be able to tell if my ovarian cyst is cancer?
Timber is right on the money. Usually ultrasounds are better at visualising ovarian cysts as they are better able to see what they contain (fluid, blood, mucous, tissue etc..). Usually a simple (fluid filled), thin walled cyst without septations (divisions) that is 5 cms or less and on one ovary will most likely go away on its own as it is probably a normal functional cyst. Cysts that are greater than 5 cms and that have solid components (ie. complex cysts) should really be biopsied to be sure, although most of these are also benign.
What a radiologist sees on the ultrasound is actually better at predicting cancer (or not) than the CA-125 blood test. The radiologist's opinion has about a 90% predictive value and the CA-125 is somewhere in the 80% range. I am not sure what the two together would give you but I assume that this would give even more reassurance. Radiologists have become extremely good at seeing cancer so you should take heart in this. However, as Timber said, to be 100% sure, you have to biopsy it and look at the cells under a microscope.
I myself have a 9 cm simple cyst that is to be removed at the end of the month by laparoscopy. Although I am reassured that all of the radiologists that have looked at the cyst say that it is harmless (they seem super sure), I will still be glad when they biopsy my left ovary and tell me FOR SURE with 100% certainty that all is well.
Hope this helps.