I have a bump on the back of my head at the base of my neck and skull. it's slightly tender. i didn't bump my head or anything. what could this be?

Mass back of head: You 'll need to see a doctor to examine the mass. It can be a lipoma, sebaceous cyst, osteoma or other tumors.

Agree with Dr. K: One other possibility is an enlarged lymph node. You may watch and wait. You may feel the bumps periodically , if the bump doubles in size, becomes painful, ulcerates, or other bumps appear, or you develop fever, or lose weight, you should see a doctor.