3 months post op tummy tuck with liposuction, seroma as per CT Scan with no fluid present.

Longstanding seromas can sometimes form a scarred cavity called a pseudocyst that may need to be excised surgically.  This may explain the lump you are feeling.  

I am a bit confused by the CT scan reading.  A seroma by definition contains fluid (serum) so I am wondering how the radiologist would call this a seroma but notes no fluid present. If I am misinterpreting the reading and there is fluid that the surgeon cannot reach with a needle, the radiologist can ofter do this using CT or ultrasound guidance to assure the needle is within the fluid filled cavity. All the best. 

You most likely have a loculated seroma cavity that has a lot of indurated tissue hence the lump you are feeling. You should give yourself time for the swelling and inflammation to improve. If it does not go down in a few months then your only option aside from living with it would be to have surgery to explore the area and remove the cavity.