Thanks for your question on Health Care Magic. I can understand your concern. By your history and description, possibility of dermoid cyst is high in your son s case. Dermoid cysts is benign soft tissue swelling common in back of neck, back, extremities etc. It is composed of calcium. This is the reason for hard feeling. Get done ultrasound examination of local part and fine needle aspiration cytology (FNAC) for the diagnosis of dermoid cyst. Usually no treatment is required, but if it increases in size or becomes painful or becomes infected than surgical removal is advised. Hope I have solved your query. Wishing good health to your son. Thanks.