Epidermoid cysts of the floor of the mouth are considered rare. New and Erich (1937) reported 24 (1.6%) epidermoid cysts occuring at the floor of the mouth out of 1495 cases of dermoid cysts seen at the Mayo Clinic.
In 1955, Meyer updated the concept of dermoid cyst to describe three histological variants: the true dermoid cyst, the epidermoid cyst and the teratoid variant. True dermoid cysts are cavities lined with epithelium showing keratinization and with identifiable skin appendages such as pilous follicles, and sudoriparous and sebaceous glands on the cyst wall. Epidermoid cysts are lined with simple squamous epithelium with afibrous wall and no attached structures. The lining of teratoid cysts varies from simple squamous to a ciliate respiratory epithelium containing derivates of ectoderm, mesoderm and/or endoderm. All three histological types contain a thick, greasy-looking material .
Most patients with epidermoid cyst are in the range between 10 and 35 years of age . In a series of 16 cases, the mean age is 27.8 years and the ratio of men/women is 3:13, although previous papers have found no difference by gender while others have found predominance of women. Growth of the cyst may be constrained by hormonal stimulus during puberty, producing a hypersecretion of fat, which would explain the greater incidence in the young adult stage (16-40 years of age) .
Anatomic classification divides the epidermoid cysts of the floor of the mouth into three groups according their relation to the muscles of the floor of the mouth: sublingual or median genioglossal cysts, located above the geniohyoid muscles; median geniohyoid cysts, located in the submental region between the geniohyoid and the mylohyoid muscles; and lateral cysts, located in the submaxillary region . The cystic mass can vary in size from a few millimeters up to 4.72 in in diameter .
The size and the location of the epidermoid cyst are the cause of the clinical manifestations. Cystic lesions developing above the mylohyoid muscle have the potential to displace the tongue toward the palate and subsequently create difficulty with mastication, speech, and possibly breathing. Cysts developing below the mylohyoid often produce a submental or submandibular swelling . In our first case the sublingual swelling suggests that the lesion was above the mylohyoid muscle, which is the most common location. The mass was located in the left side of the floor of the mouth, pushing the tongue to the right side. The second patient had a well circumscribed swelling in the left submandibular region. It was complaining of dysphagia, dysarthria and dyspnoea on exertion.
When dealing with swellings in the floor of the mouth and neck region, 4 main groups of lesions should be considered: infections, tumors, mucous extravasation phenomena and anatomic abnormalities arising during embryonic development. In our cases, the hypothesis of an infection was discarded due to the period of evolution and the absence of pain and of intraoral infectious foci. Malignant tumor was ruled out in view of the lesion's clinical aspect and the absence of lymphadenopathy, although the latter is admittedly an imprecise indicator of malignancy. It was possible then left with two main diagnostic possibilities: a mucous extravasation phenomenon and an anatomic abnormality. Because the clinical aspect was compatible with ranula and because ranulas are far more common than epidermoid cysts, this was our first hypothesis. In some instances, where the differential diagnosis of sublingual swellings is more challenging, imaging techniques may be used for preoperative diagnosis and surgical planning. Fine-needle aspiration is not always diagnostic. Magnetic resonance imaging (MRI) and computed tomography (CT) allow more precise localization of the lesion, and also enable the surgeon to choose the most appropriate approach. Thus, microscopic examination will always be required following excision of the lesion .
Surgical enucleation is the only effective treatment for these kinds of lesions. Several techniques are reported in the literature, which may be divided into intraoral and extraoral techniques depending on which approach is used.
In the case of an intraoral approach, a midline vertical, mucosal incision is performed along the ventral surface of the tongue; however, only small cysts can be enucleated using this kind of incision . Lowry et al.  describe a bilateral incision along the mandibular ridge crest, Brusati et al.  propose a midline glossotomy, and Di Fransesco et al  describe a modification of this surgical technique consisting of an extension of this incision along the ventral surface of the tongue associated with partial evacuation of the epidermoid cyst. The latter two techniques, according to Longo et al  allow to obtain a very good approach to the cyst and to obtain adequate surgical control of the lesion in the event of median cysts located above the geniohyoid muscles.
The transcutaneous approach consists of a submental incision and a sharp, blunt dissection to reach and enucleate the lesion . Mc Gregor  describes a symphyseal mandibular osteotomy to enucleate a very large sublingual dermoid cyst. The extraoral approach is generally preferred in the case of median geniohyoid or very large sublingual cysts, whereas the intraoral approach is typically used for smaller sublingual cysts.
In the current first case, excision was achieved without major complications by employing intraoral access under general anestesia. The elliptical incision was made on the floor of the mouth, followed by blunt dissection. The lesion was found sitting on top of the genioglossus muscle. In the current second case we adopted a transcutaneous approach. Under general anaesthesia, a transverse incision was made in the left submandibular area extending beyond the midline to the opposite side. This was carried through skin, subcutaneous tissue and platysma. Blunt dissection was utilized to free the mass, which was removed intact after which the right submandibular gland was reposited within its capsular bed. The wound was sutured in layers and a corrugated rubber drain was placed in position. The postoperative course does not present any kind of problem because there is little alteration in function, edema is generally modest, and complications are unusuall.
Prognosis is very good, with a very low incidence of relapse, usually related to bone remnant to the genial tubercles or to the hyoid bone. Malignant changes have been recorded in dermoid cysts by New and Erich  but not in the floor of the mouth, although a 5% rate of malignant transformation of oral dermoid cysts has been reported by other authors, but only for the teratoid type .