Unfortunately, a CT scan can miss cancerous tumors. CT scans can only pick up something thats bigger than 2 or 3 cm which is very small (about the size of a grain of rice). Cancerous tumors are at the cellular level, (with my medically uneducated background) I cant begin to even guess how many cells would make up a cm??? CTs are less expensive and quicker than other scans which could be why they are used so often. The CT scan takes slices of whatever area of the body the doc wants more info about. The patient has the CT done which gets sent to the pathologist to read (at least thats how it is here in the US). The pathologists report is sent to the ordering physician and the doc will relay the results to their patient. As with anything, nothing is ever 100% guaranteed as there are so many variables involved including the possibility of good old human error. Heres more info....

Main OCF Site, Diagnostic Imaging

As far as the enlarged nodes are concerned it could be from all kinds of things including a sign of an infection. If your doc didnt mention the enlarged nodes it could simply be an oversight. If you arent convinced after the CT and what the doc said, it would be wise to go for another opinion (at a different medical facility thats not affiliated with your current doc). I suggest writing down all your questions to ask your doc at your next appointment, you could also email the doc (if available) or call the doc to ask your questions over the phone.