Dermoid cyst with tooth. X-ray of the pelvis of a 36 year old woman showing a dermoid cyst containing a tooth. The dermoid cyst is seen at centre left (dark region) with a tooth embedded (white, at near centre). Bones of the pelvis are at upper left and right, with the thigh-bones at lower left and right. A dermoid cyst is a benign tumour, usually present from birth, that contains fatty tissue. Some dermoid cysts contain misplaced tissue types such as fragments of bone, cartilage, or in this case a tooth. They occur as painless swellings, sometimes after injury, but may cause discomfort and abdominal swelling. Treatment is by surgical removal in most cases.