Can a ct scan detect recurrence of a femoral hernia?

Yes: But not always. A ct scan is not a dynamic study and will not always show hernia defects unless there is something herniating through it. A better study is an ultrasound, which is done both standing and recumbent, and with maneuvers to increase intra-abdominal pressure. Additionally, evaluation by a surgeon would be worthwhile.

Maybe: Ct scan is a good test, but not perfect. If you are considering this, you don't need any oral or IV contrast, and should be done with and without valsalva (bearing down).