Hi there, the cyst is of a large size and it is good that you are getting this CT scan. You are going to worry no matter what, but you are being pro-active. Be sure that you do see a specialist regarding this cyst. Please keep us updated.
There really is no normal size for a cyst. But the rule of thumb is that when it gets to be around 5 cm, most doctors will opt to remove it. There is no way to tell if it is cancer until a biopsy is done at the time of removal, but both malignant and benign can grow that large. It's easy for me to tell you not to worry, but the fact is that between 90% and 95% of cysts are not cancer. So the odds are on your side. The CT scan will give your doctor a better picture of the areas involved, and if anything shows up anywhere else. I know it is stressful to wait. When are you having the CT Scan?