[Giant dermoid cyst of the floor of the mouth].

Report the case of a young feminine patient, 17, presenting since the first year of her life, a swelling of few milimeters diameter, close to the frenulum of the tongue, with progressive enlargement. At examination is verified a swelling about 10 cms. diameter filling the whole ground of the mouth and pulling backwards the tongue and producing a clear protrusion in the suprahyoid region. After lateral X-ray of the neck, echography and cervical TAC, surgery is advised with the suspicion of ranula sublingualis. Removal of the tumor through medial cervictomy, finding, besides the main mass, a second one about 3 cms. diameter. The histopathological diagnosis of a cyst of the thyroglossal duct, its sitting place and the clinical course, compelled the AA. to review the slides and being obvious the presence of sebaceus glands, they change the prior diagnosis for that of dermoid cyst.