Hard lump after seroma? (photo)

Thank you for your pictures.  This may represent scar tissue for the seroma and the drainage procedures.  I would recommend an examination by your plastic surgeon to determine the true nature of this area.

Your surgeon who has followed your recovery will probably have a better idea of what happened here as compared with on line surgeons seeing a picture of one moment in time.  It looks like the tissues around the seroma were injured resulting in thinning of the fat that is under the skin, and perhaps weakening of the suture repair of the abdominal muscles. It may be that the only correction will involve repeating the tummy tuck, redoing the muscle repair, and  redraping the skin.All the best. 

Good Question!  Having a serum in an area will delay that area healing until it is resolved, therefore, it is not abnormal to have more swelling where a serum "was".  That said, If there still is a serum, it can "organize" and lead to a long term deformity.  In our practice we ultrasound using and image ultrasound device (similar to what you do with a pregnancy to look at the baby).  Sometimes there is still fluid that needs to be drained and using needle alone will sometimes miss it.  I would definitely bring up your concern with your surgeon!