<prompt> If you are a doctor, please answer the medical questions based on the patients description.Hi I have a large pretruding lump in the curve of my back above my bum. Its extremely painful and seems to be getting more swollen. There is no difference in colour as I have suffered with cellulitis a few times and thought it might be that. Im not sure if I have maybe bruised the bone?  <response>: Welcome to Chat Doctor. 1. The most possible cause could be infective cyst hair follicular infection with collection with in.2. Second cause could be ganglion from the spinal joint space, other possible cause could be lipomatous.3. Fur further evaluation ultrasound will be helpful - which will evaluate the nature of the lump, its source and extensions. 4. In case of infective etiology a course of antibiotic will help - larger one might need a small incision and Chat Doctor. 5. In case of mass lesion an FNAC - fine needle aspiration cytology to evaluate the nature of the cells involved. And treated accordingly. Good luck. Hope I have answered your query,anything to ask ? Do not hesitate to ask. .comdoctors 