Dermoid cyst of the floor of the mouth

 A large dermoid cyst of the floor of the mouth is reported. The cyst was successfully treated by surgery. The etiology of swellings of the floor of the mouth is reviewed with special reference to the clinical features of the case described.

Case Report
A 50-year-old Saudi male reported to the Riyadh Dental Center with a painless swelling in the floor of the mouth of ten years duration, and with associated difficulty of speech and swallowing. The swelling had been steadily increasing in size during the previous two years.
Extraoral examination showed a well cir­ cumscribed mass fully occupying the submental region. The overlying skin was normal [Fig. 1] with­ out clinically palpable regional lymph nodes.
Intraoral examination revealed a big swelling in the floor of the mouth pushing the tongue upwards [Fig. 2]. The overlying mucosa covering the swel­ ling was normal and saliva could be expressed from the orifices of Wharton's duct. On bimanual palpa­ tion, the mass was well circumscribed, roughly rounded and of doughy consistency. Fluctuation could be elicited bimanually. Needle aspiration yielded a thick, whitish, creamy material.
The clinical diagnosis of a dermoid cyst was established. Patient underwent routine investiga­ tions before he was operated under general anes­ thesia. The lesion was enucleated en toto through an intraoral approach. The tissue was sent for his-topathological examination, the report of which was consistent with the clinical diagnosis [Fig. 3]. The  histopathological   report  read:   "The cystic space Is lined with keratinized stratified squamous epithelium containing keratin-like material. Although this field does not show any skin appen­ dages but intra-operatively, hairs were seen in the cystic cavity"
The post-operative phase was uneventful. The swelling disappeared [Figs. 4, 5] allowing the patient to swallow and articulate normally. He was discharged after seven days. At present, he has completed 12 months post-operatively without any complaints.
Differentia! Diagnosis
Swellings in the floor of the mouth are not com­ mon and they fall into three groups, namely, infec­  tious, neoplastic, and cystic (developmental).
Infectious group includes several diagnostic pos­ sibilities. If the lesion is nodal in origin, enlarge­ ments to be considered include non-specific adenitis, cat-scratch disease, tuberculosis, infecti­ ous mononucleosis and sarcoidosis. An infectious etiology was unlikely in this case because the dura­ tion was long and symptoms were attributed to the bulk of the swelling.
Neoplastic lesions must be considered in any situation with a persistent, steadily enlarging mass. The most likely neoplasms in this location are benign and malignant salivary gland tumors, cystic hygroma, primary lymphomas and nodal metas­ tasis. A neoplasm may be cystic but, in the case presented, clinical signs and symptoms did not point towards a neoplasm.
From the history and clinical presentation of this case, a cystic lesion was the most probable diag­ nosis. Cystic lesions in this location which were considered, included dermoid cyst, branchial cyst, a thyrogiossal cyst, and a plunging ranula. Of these, the least likely was the branchial cyst which normally presents as a more laterally located lesion containing thin, watery fluid, or thick mucoid material.1 The plunging ranula was ruled out because the overlying mucosa in this case was of normal color and the mass was positioned symmet­ rically, both intraorally and submentally. Dermoid cyst often occurs in the floor of the mouth, originat­ ing either deep or superficial to the mylohyoid mus­ cle. It can grow to a rather large size and interfere with speaking or swallowing. The needle aspirate in this case was consistent with the classical textbook description.1 A dermoid cyst was, there­ fore, the most likely clinical diagnosis for this patient, and this was confirmed by the histological report.

The pathogenesis of dermoid cysts located in the floor of the mouth is not definitively established. A number of investigations support the theory of embryological epithelium implantation, whereas others propose the theory of traumatic implanta­ tion of epithelium. The complex embryologic development of structures of the floor of the mouth, the consistency with the clinical picture, and the usual absence of significant injury to the area suggest that most of these are congenital and not traumatic in origin.2
Dermoid cysts have been classified as median and lateral. The two differ in their origin and clinical presentation. The median cyst lies in the connec­ tive tissue beneath the lingual frenum. As they increase in size, they push apart the genioglossus muscle, growing deeper into the floor of the mouth and backwards into the tongue.3 Lateral dermoid cyst on the other hand lies in the depth of the mus­ cular gutter formed by the mylohyoid muscle later­ ally, and the genioglossus and geniohyoid muscle medially.4,5 However, when these cysts reach
large sizes, it becomes difficult to differentiate between median and lateral types.
Histologically, dermoid cysts are divided into three types.6,7 The simple and most common type is epidermoid in which the cyst wall is lined by stratified squamous epithelium, which may be partly keratinized. The compound dermoid type is similar to the epidermoid but the epithelial lining and wall shows evidence of skin appendages. The third and rarest is the teratoid type which contains mesodermal tissue derivatives, such as muscle in addition to adnexal structures.
Dermoid cysts are more common in the second and third decades of life8 but our case was in the fifth decade which was unusual. The cyst varies in size and consistency depending on the content.1
The surgical removal of a large dermoid cyst in the floor of the mouth using an intraoral approach is difficult. In cases where the cyst is below the geniohyoid muscle, however, many surgeons pre­ fer the extraoral approach.9,10 After complete exci­ sion, dermoid cysts of the floor of the mouth do not recur. Malignant changes in these cysts had been reported11 but only in cysts occurring outside the oral cavity.