ⅠINTRODUCTION

Dermoid cysts are rare developmental cysts located at the floor of the mouth. New and Erich reviewed 1,495 dermoid cysts. They found that only 103 (6.94%) occurred in the head and neck area, and of these, only 24 (1.6%) were located at the floor of the mouth¹⁾. The pathogenesis of cysts at the floor of the mouth is not well established, but some theories of dysontogenetic, traumatic, and thyroglossal duct anomaly have been suggested²⁾.

Cysts at the floor of the mouth can be divided into 3 histological groups: dermoid, epidermoid, and teratoid. Although dermoid cysts represent a separate entity, the term “dermoid” has generally been used to indicate all 3 categories^3,4). Most of the reported intraoral dermoid cysts were located in the mid-floor of the mouth, superior to the mylohyoid and geniohyoid muscles⁵⁾. Several investigators suggested that cysts may also arise below the mylohyoid muscle^6,7). If a cyst is located above the mylohyoid and genioglossal muscles, swelling of the mouth floor causes elevation of the tongue, which can affect speech, eating, and even breathing⁸⁾. If it is located between the geniohyoid and mylohyoid muscles or under both muscles, it presents swelling of the submental space, which gives the double chin appearance⁹⁾. Dermoid cysts located lateral to the musculature of the tongue are rare, and a total of only 13 cases have reported in the literature^10-12). The vast majority of dermoid cysts on the floor of the mouth are located at the midline (sublingual 52%, submental 26%), 16% of them involve more than 1 of the 3 possible spaces in the floor of the mouth region (submental, sublingual, submandibular), and only 6% are situated exclusively in the submandibular space¹¹⁾. Some authors have investigated the existence of a lateral variety, claiming that a centrally located cyst simply becomes displaced laterally during growth, but no explanation has been reported as to why some expand laterally and other cysts remain only at the midline^8,9,13).

Histologically, all dermoids are lined by the epidermis. If adenexae, such as sweat glands, sebaceous glands, and hair follicles, are present, the cyst is referred to as a “true” dermoid cyst^6,14). The location of the cyst appears to be a factor for determining the surgical approach^7,13-15). Seward and Rapidis et al. suggested that almost all of the cysts at the floor of the mouth can be removed intraorally, with patience, unless large blood vessels are located adjacent to the cyst^5,13). Large cysts that are located around the mylohyoid or those that perforate the mylohyoid may require both intraoral and extraoral incisions to provide direct visualization of important adjacent structures^16,17). All clinicians agree that total excision is the method of treatment. Sharp dissection may be necessary if infection episodes or fibrous adhesions exist^18,19). Dermoid cysts do not recur if the original cyst was completely excised^16,20,21). Some large dermoid cysts can cause significant airway obstruction or may become enlarged to a huge size that makes intubation impossible or extremely difficult. Tracheostomies have been performed when intubation was considered difficult or impossible ^22,23).

This article reviews three cases of unusual dermoid cysts. We present 2 cases of dermoid cysts with an unusual lateral location and 1 case of a dermoid cyst with a large size occurring at the floor of the mouth.

ⅡMATERIALS and METHODS

This study was approved by the Institutional Review Board of the Chosun University, School of Dentistry. We included paraffin-embedded tissues from 3 cases of oral dermoid cysts. Cases were retrieved from the archives of the Chosun University Dental Hospital. All patients’ records were kept confidential and made accessible only to the research group.

ⅢRESULTS

1Case Ⅰ

A 66-year-old woman had a non-tender soft mass that was visible on the left floor of the mouth (Fig. 1A). The patient was not aware of its presence until an examination. A tentative diagnosis was made of a plunging ranula and dermoid cyst at the floor of the mouth. An enhanced CT scan was performed. In the CT views, the boundaries radiographically delineated the cyst from the floor of the mouth to the submandibular space (Fig. 1B). The cyst was removed using an intra-oral approach, and the lesion contained a cloudy yellow material. The wound was closed with 5-0 Vicryl. A histopathologic examination was performed, and the lesion was identified as a dermoid cyst filled with keratin and lined with stratified keratinizing squamous epithelium (Fig. 1C). The postoperative healing was good without any complications. There was no recurrence over 59 months.

2Case Ⅱ

A 41-year-old man had a non-tender swelling in the left submandibular area. The patient had been aware of its presence for 1 year. The examination showed a doughy-like lesion of approximately 5 X 3 cm that could be bimanually palpated through the floor of the mouth and the submandibular skin. Enhanced CT images were obtained. The boundaries radiographically delineated the cyst from the left and anterior floor of the mouth to the superior border of the hyoid bone. The lesion was well-circumscribed and extended without enhancement upon contrast material injection between the left lingual aspect of the mandible and the hyoid bone filling the submental and left submandibular spaces (Fig. 2A). There was no ‘tail sign’, so we were able to rule out the ranula in the CT axial image. The tentative diagnosis was made of a dermoid cyst.

The lesion was located primarily in the submental and left submandibular regions, thus the intra- and extra-oral approach was selected. An incision of approximately 3 cm was made at the left submandibular area (Fig. 2B). The lesion was removed through the intraoral incision site, and we used the extraoral approach for the inferior dissection of the lesion. This approach allowed for bimanual manipulation to free the cyst and deliver it intact. After removal, the lesion was measured and the size was approximately 5.5 X 4 cm. The lesion was incised and found to be cystic, and it was filled with a thick, white, cheesy material. A definitive histopathologic examination confirmed that the lesion as a dermoid cyst, and the contents were primarily keratin. The postoperative course was good at both operation sites, and there was no recurrence over 23 months.

3Case Ⅲ

A 28-year-old man had a large painless swelling at the floor of his mouth and an elevated tongue. He had some difficulties with eating, speaking and breathing. The patient had been aware of the swelling for 4 years. A physical examination revealed a doughy-like lesion at the mid-floor of the mouth and a swelling on the submental, submandibular, sublingual areas that could be bimanually palpated through the floor of the mouth and the submandibular skin. An MRI was performed (Fig. 3A). The boundaries radiographically delineated the cyst throughout the floor of the mouth to the superior border of the hyoid bone. The lesion was a well-circumscribed lesion extending between the left lingual aspect of the mandible and the hyoid bone, filling the submental and submandibular spaces. There was no ‘tail sign’, so we could rule out the ranula based on the axial MRI axial. A tentative diagnosis was made of a dermoid cyst. The sagittal and coronal images showed a large, well-circumscribed, unilocular lesion filling the entire floor of the mouth. The lesion extended anteriorly to the lingual surface of the mandible. Below the mandible, the cyst wall and possibly some geniohyoid and mylohyoid remnants were displaced inferiorly. The dorsal surface of the tongue was displaced superiorly and posteriorly. The posterior border of the lesion was defined by the displaced intrinsic muscles of the tongue. The oropharynx was narrowed antero-posteriorly. The lesion had perforated the genioglossus muscle, and these muscle fibers, along with the geniohyoid muscles, formed the lateral boundaries of the lesion.

A tracheostomy was performed because of a failed endotracheal intubation. A midline incision was made to the sublingual and mid-floor of the mouth. The lesion was delivered through the midline incision and by blunt dissection using the fingers (Fig. 3B). The wound was closed, and a silastic drain was inserted. Intraorally, the incision was linear in the midline, through the mucosa to the fibrous capsule of the cyst. The mass could be partially isolated from the floor of the mouth. Care was taken to identify and lateralize the lingual arteries and nerves. The dissection was carried to the level of the genial tubercles and the mylohyoid ridge.

The lesion had a cystic structure and measured 7 X 6 X 5 cm. It was filled with a yellowish cheese-like material. A definitive histopathologic examination identified the lesion as a dermoid cyst. The cyst was lined with a layer of keratinized squamous epithelium and contained keratin lamellae. Adnexal structures were observed in the cavity. Grossly, the specimen was an intact, doughy, cystic sack. On dissection, it was found to consist of a thin membranous wall surrounding a thick, granular, yellowish paste. Microscopic examination of representative stained tissue sections revealed a fibrous wall lined in part by a uniform, thin layer of orthokeratinized stratified squamous epithelium and in part by granulated tissue consisting largely of macrophages and giant cells reacting to the keratin of the cyst contents. The wall of the cyst showed duct-like structures that were interpreted to represent residual ducts of the skin adnexal structures and multiple foci of smooth muscle, analogous to the erector pili muscles of the skin. There was no postoperative compromise of the airway. The recovery was uneventful. The drain was removed at 2 days after the operation. A follow-up examination at 2 weeks showed normal healing of both incisions. Interestingly, the patient reported resolution of his snoring problem. There was no recurrence over 40 months.

ⅣDISCUSSION

Dermoid cysts in the floor of the mouth are uncommon tumors occurring at the midline in most cases^9,24). They typically present in the second or third decades of life as painless, slow-growing masses in the floor of the mouth, submentum or anterior neck²⁵⁾.

Depending on their location, these cysts are classified into two types. First, the sublingual type is located between the oral mucosa and the geniohyoid muscle, which causes an upward displacement of the tongue. Depending on the size of the cyst, it will give rise to specific symptoms. Second, the submental type arising between the geniohyoid muscle, the mylohyoid muscle and the skin is referred to as a geniohyoid cyst with an outward displacement that resembles a double chin ^24-26). These cysts are distinguished into two groups, the midline type and the lateral type. The midline type occurs at the junction of the tuberculum impar with horizontal processes growing medially from the first branchial arch in the development of the anterior tongue. The lateral type most likely arises from the ventral end of the first pharyngeal pouch or from the extreme ventral end of the first branchial cleft⁵⁾.

Teszler and colleagues developed an anatomico-surgical classification system of dermoid cysts at the floor of mouth to assist surgeons when making decisions in the process of the surgical approach¹²⁾. In their algorithm, a dermoid cyst can be grouped into one of seven classes based on its median versus lateral location and its relationships to the mylohyoid and geniohyoid muscles¹²⁾. Complete enucleation of dermoid cysts at the floor of the mouth may be an effective treatment. Whether the surgical approach should be intraoral or extraoral via a submental skin incision is under discussion. Various techniques have been reported in the literature, differing according to the size and site of the lesion²⁵⁾. The extraoral approach is generally preferred in the case of median geniohyoid or very large cysts of the floor of the mouth, whereas the intraoral approach is the typical surgical technique used for smaller cysts^27,28).

Differential diagnosis of swelling of the neck and floor of the mouth includes lipoma, Ludwig's angina, acute infection or cellulitis of the floor of the mouth, ranula, thyroglossal duct cyst, cystic hygroma, cystic lymphangioma, unilateral or bilateral blockage of Wharton's ducts, branchial cleft cysts and benign or malignant neoplasms of the mucosa or salivary glands^29-31).

There are various types of diagnostic imaging modalities such as CT, magnetic resonance imaging, and ultrasonography^32,33). CT and magnetic resonance imaging offer superior tissue characterization and more precise anatomical localization compared to the regional musculature, which enables the surgeon to accurately plan an appropriate surgical approach²⁵⁾. CT imaging of dermoid cysts has been reported to show the characteristic xenotypic ‘‘sack of marbles’’ configuration, and recently, similar findings have also been demonstrated with MRI⁷⁾. The smaller foci within the cyst seem to result from a coalescence of lipid and keratinous material, resulting in a unique radiologic appearance that may be considered a pathological characteristic of dermoid cysts⁷⁾.

The only effective treatment for these lesions is surgical enucleation using various surgical approaches described depending on the location of the lesion relative to the geniohyoid and mylohyoid muscles. Enucleation is a typical treatment method, sometimes with preoperative decompression²⁸⁾. Midline sublingual dermoids may be treated using an intraoral approach, however this option may result in difficulty achieving hemostasis³⁴⁾. Submental dermoids are approached using a transverse submental skin incision. The relationship to the anatomic structures and the ability to safely visualize the surgical field are the critical elements when choosing a surgical approach²⁵⁾. An intraoral approach is recommended for a large midline cyst lying above the mylohyoid muscle³⁵⁾. Longo et al.25) recommended the intraoral approach for the treatment of large lesions presenting above the mylohyoid muscle to obtain good cosmetic and functional outcomes. This approach was utilized in the first and third case because the cyst was not infected; it was found to be an easy technique to perform that can produce good cosmetic and functional results with no complications. The extraoral approach is utilized for large dermoid cysts that simultaneously involve the floor of the mouth and the submental space and in cases of severe infection that compromise the patient’s airway²⁸⁾. For large cysts, the transcervical approach is favored, providing superior access and convenience in the delivery of the lesion^25,27,36-38). In the case of a very large, intact cyst, the use of a combined oral and dermal approach may be necessary to ensure adequate visualization of important adjacent structures²⁸⁾. King et al. suggest that both techniques are successful and can be used at the surgeon’s discretion¹¹⁾. Of the 8 trans-geniohyoid dermoids for which the surgical approach was reported, 6 were removed via the oral route only^34,39), 2 via a combined oral/dermal route⁴⁰⁾, and none via the dermal route alone. Measuring the clinical or radiographic size of the lesion to choose a surgical approach is not appropriate in itself because of the variation in the size of the jaws of patients in which a dermoid cyst may occur, ranging from newborns to adults. The relationship to anatomic structures and the ability to safely visualize the surgical field are the critical elements when choosing a surgical approach⁸⁾. The combined approach allows bimanual manipulation to free the cyst and deliver it, intact, through the mouth⁴¹⁾. In our second case, an attempt to remove the cyst through an oral and submandibular approach was used for the bimanual dissection.

In cases of large sublingual and submental lesions, anesthetic difficulties should be considered and fiberoptic intubation must be planned to avoid emergency tracheostomy²⁵⁾. Although a moderate degree of postoperative edema is expected, airway obstruction is unusual, given the space created by cyst removal. Close postoperative monitoring of these patients should be the standard²⁵⁾. Various surgical techniques were reported for enucleation of the dermoid cysts at the floor of the mouth, including vertical midline bilateral incision along the mandibular crest, midline glossotomy, modified midline glossotomy and transcutaneus approaches³⁾. Deromid cysts above the geniohyoid muscle are enucleated via an oral access, while the submental lesions are removed through the skin. The removal of large intact lesions may not be possible through these routes alone, and decompression or a combined surgical approach may be necessary. The location of the cyst relative to the geniohyoid muscle is critical to the clinical presentation. Those lesions presenting above the geniohyoid produce sublingual swelling, forcing the tongue upwards and backwards. Patients with large lesions may suffer from dysphagia and/or dysphonia^21,27,42). Lesions occurring below the geniohyoid muscle produce a well-circumscribed submental swelling beneath the skin. When a lesion is large enough, a submental mass is clinically visible^8,27). Particularly large lesions may extend through the geniohyoid muscle barrier, producing clinical features in both the sublingual and submental areas²⁷⁾. The location of a dermoid cyst relative to the genioglossus, geniohyoid, mylohyoid, digastric and platysma muscles has been suggested to determine the most appropriate means of surgical excision of the mass, including intraoral, submental and submandibular approaches^21,27). MRI has been reported to show superiority over other imaging modalities in demonstrating the exact location and extent of cystic lesions of the floor of the mouth³⁷⁾. Although the MRI findings in isolation could imply that an intraoral approach would have been the preferred means of accessing and excising the lesion in this case, the lateral cervical presentation of the mass in the submandibular region and the immense size of the cyst favored a transcervical approach, as has been suggested by others^21,27,42). Surgical excision is the only effective treatment for dermoid cysts. Recurrence is rare and is typically related to cyst remnants left on the genial tubercle or hyoid bone42). Similarly, malignant degeneration of dermoid cysts of the floor of the mouth is exceedingly uncommon and has only been reported in patients with lesions of the teratoid subtype^37,42).

Histologically, dermoid cysts are differentiated from epidermoid cysts by the presence of an epidermoid lining containing adnexal structures such as sweat glands, sebaceous glands, hair, and hair follicles^36,37). Clinically, these lesions are benign, painless, and slow-growing; however, when the lesion is long-standing, malignant transformation has been reported, though it is exceedingly rare⁴³⁾. Cystic contents are variably keratinous, caseous, sebaceous, or purulent with hair, nails, fat globules, cholesterol clefts, and even cartilage^44,45). Dermoid cysts can be distinguished from ranula on this basis by fine-needle aspiration⁴⁴⁾.

In this report, 3 cases are presented, and two lateral varieties of dermoid cysts and one large dermoid cyst were removed using an intraoral approach successfully. Generally, intraoral dermoid cysts exhibit painless growth and a doughy quality on palpation with no tenderness, as was observed in these three cases. Most reported cases were located at the mouth floor, superior to the mylohyoid and geniohyoid muscles, but occasionally, as in case 2, the cyst may be located between the geniohyoid and mylohyoid muscle and require an extraoral approach. In case 3, a tracheostomy was performed when intubation was extremely difficult because the large lesion had significantly compromised the airway.

A dermoid cyst could be diagnosed by clinical examination and radiologic examination, especially CT image and MRI. In CT and MRI images, dermoid cysts are unilocular, showing a smooth margin and a well-demarcated cyst wall. The contents are all homogenous, and dermoid cysts do not have a tail sign, compared to the ranula.

Generally, total excision is the most typical and effective method of treatments, and the cyst does not recur if the excision is complete. In the cases described here, no recurrence was shown after surgical enucleation for 57 months (case 1), 22 months (case 2), and 39 months (case 3).