ENT Dr. Can re-check. A person who had a drainage tube after surgery, and now with the tube gone, has a lump at the hole where the drainage tube had come through, might have some scar tissue forming at that site, some material trying to get out (but stuck inside the skin because the drainage tube is gone, and the skin sealed up), or some other problem. A return visit to the ENT surgeon can figure out the problem.
Location. Where is the nodule? Was it a drain in the incision? Need more information as to the location of the nodule. If you had a mastoidectomy, you have had chronic middle ear disease. The nodule may only represent a fibrous thickening. Is it tender? We need to know this information before we can give you the answer and appropriate treatment. The nodule can be removed.