Dermoid cyst

The dermoid cyst is a benign developmental cyst arising from ectodermal tissue entrapped along embryonic fusion lines.[1][2] In the oral and maxillofacial region, the lesion results from sequestration of surface ectoderm during closure of the mandibular and hyoid branchial arches, leading to a cyst lined by keratinized stratified squamous epithelium with skin adnexal structures (hair follicles, sebaceous glands, sweat glands) in the cyst wall.[3][4][5] The floor of the mouth is the predominant oral site, where the cyst characteristically presents as a slow-growing, painless, midline or paramedian soft-tissue mass.[5][6] Because the lesion is a soft-tissue entity, it is typically not visible on conventional dental radiographs unless it is large enough to displace or resorb adjacent osseous structures; cross-sectional imaging (CT, MRI) is the primary modality for characterization.[7][8] Intraosseous dermoid cysts of the jaws are exceedingly rare.[9][10][11] Complete surgical excision is curative, with very low recurrence.[12][13]

Current nomenclature

In oral and maxillofacial surgery, the term "dermoid cyst" is used broadly to encompass three histologic variants of congenital floor-of-mouth cysts:[5][14]

• Epidermoid — lined by keratinized stratified squamous epithelium only
• Dermoid (true) — epithelial lining plus skin adnexal structures (sebaceous glands, hair follicles, sweat glands)
• Teratoid — contains tissues derived from all three embryonic germ layers

This tripartite classification, originally attributed to Meyer (1955), remains widely used.[5][14] Gordon et al. proposed the alternative term "congenital germline fusion cyst" to more accurately reflect the embryologic origin and to encompass all three variants under a single descriptor.[14] The term "dermoid" is also used in dermatology and neurosurgery with slightly different connotations; in the head and neck, it should not be confused with ovarian "dermoid cysts," which are mature cystic teratomas.[15]

Obsolete or confusing usage

Use of "dermoid cyst" as a synonym for teratoma is discouraged in the oral and maxillofacial literature.[4][14]

• Less than 7% of all dermoid cysts involve the head and neck; only approximately 1.6% occur in the oral cavity.[1][2]
• Among oral pathology archives, dermoid and epidermoid cysts each represent fewer than 0.1% of accessioned specimens.[1]
• The floor of the mouth accounts for roughly 13–26% of head and neck dermoid cysts, making it the most common oral site.[2][6]
• Mean age at presentation is in the second to fourth decades (mean ~37 years in one 48-year series), although the lesion can present at any age, including the neonatal period.[1][5][7]
• A slight female predominance has been reported for oral dermoid cysts (approximately 71% female in one series), though some head and neck series show an equal sex ratio.[1][2]
• Rare oral sites include the tongue, lips, buccal mucosa, and palate.[16]
• Intraosseous dermoid cysts of the mandible or maxilla are exceedingly rare, with fewer than ten documented cases.[9][11]

Presentation

• The classic presentation is a slow-growing, painless, doughy or rubbery, midline or paramedian swelling in the floor of the mouth.[5][6][17]
• Sublingual-type cysts (above the mylohyoid muscle) elevate the tongue and produce intraoral fullness; submental-type cysts (below the mylohyoid) present as an external submental mass.[18][19]
• Occasionally a cyst extends through or around the mylohyoid, producing both intraoral and extraoral components.[18][19]

Symptoms and complications

• Small cysts are typically asymptomatic and may be discovered incidentally.[6]
• Progressive enlargement can cause dysphagia, dysarthria, globus sensation, and, in extreme cases, airway compromise.[6][17][20]
• Rapid enlargement during pregnancy has been reported, attributed to hormonal stimulation of glandular elements.[21]
• Secondary infection is uncommon but can cause acute pain and swelling.[22]

Examination findings

• Firm to fluctuant, non-tender, well-circumscribed mass; overlying mucosa is normal in color.[6][23]
• Bimanual palpation distinguishes sublingual from submental location relative to the mylohyoid.[18][24]
• The "double chin" sign describes the submental bulge seen with large submental-type cysts.[6]

Oral dermoid cysts are predominantly soft-tissue lesions; they are generally not visible on conventional intraoral or panoramic radiographs unless they are large enough to cause secondary osseous changes or unless the rare intraosseous variant is present.[9][10][11] The radiographic discussion therefore centers on the uncommon intraosseous form and on CBCT findings relevant to dental practice.

Location and distribution

• The vast majority of oral dermoid cysts arise in the midline or paramedian floor of the mouth as soft-tissue masses and produce no primary osseous abnormality on dental radiographs.[1][5]
• Intraosseous dermoid cysts of the jaws are exceedingly rare. Reported sites include the mandibular body near the inferior border and the anterior maxilla. Takeda et al. documented multiple latent intraosseous dermoid microcysts near the inferior border of the mandible, hypothesized to arise from stomadeal ectoderm entrapped during embryogenesis.[9][10][11]

Periphery and shape

• When an intraosseous dermoid cyst is large enough to be detected radiographically, it appears as a well-defined, unilocular radiolucency with a corticated border.[10][25]
• The shape is typically round to ovoid.[10]

Internal architecture

• The internal structure is radiolucent (cystic) on conventional radiographs.[10][25]
• On CBCT, the cyst contents may show heterogeneous density if keratinous debris, calcification, or fat is present within the lumen, though this is better characterized on medical CT.[4][26]
• Rare calcified foci (teeth, bone fragments) within a teratoid variant may appear as radiopaque internal structures.[4]

Effects on teeth and adjacent structures

• Large floor-of-mouth dermoid cysts can displace teeth or cause pressure resorption of the lingual cortex of the mandible.[6][8]
• Tooth displacement without root resorption is the expected pattern for a slow-growing benign cyst; root resorption is not a typical feature.[6]
• The sublingual gland and submandibular duct may be displaced by the expanding mass, identifiable on CBCT or cross-sectional imaging.[8]

Extent and cortical involvement

• CBCT is useful for evaluating the relationship of a large floor-of-mouth dermoid cyst to the lingual cortex of the mandible, the mylohyoid muscle attachment, and the mandibular canal.[8][27]
• Cortical thinning or smooth remodeling of the lingual mandibular cortex may be seen with large sublingual cysts; cortical perforation is uncommon.[8]
• For the rare intraosseous variant, expansion with cortical thinning but intact cortical outline is expected.[10]

Variants

• Intraosseous dermoid cyst: Presents as a well-defined unilocular radiolucency within the jaw bone, indistinguishable radiographically from other benign cysts without histopathologic examination.[9][10][11]
• Giant dermoid cyst: Cysts exceeding 5–7 cm can produce significant osseous remodeling visible on panoramic radiography as smooth concavity of the lingual mandibular surface.[6][28]

CT characteristics

• On medical CT, dermoid cysts typically appear as well-circumscribed, unilocular, low-attenuation masses. Fat-density contents (negative Hounsfield unit values) are characteristic when sebaceous material predominates.[4][29][30]
• Heterogeneous attenuation may be seen when the cyst contains a mixture of keratinous debris, lipid, and proteinaceous fluid.[4][30]
• The cyst wall is thin and may show faint peripheral enhancement after contrast administration; the cyst contents do not enhance.[4][30]
• A fat–fluid level within the cyst is occasionally observed and is highly suggestive of the diagnosis.[4]
• CT clearly delineates the relationship to the mylohyoid muscle, distinguishing sublingual from submental location, which guides surgical approach.[8][18]

MRI characteristics

• MRI is the preferred modality for soft-tissue characterization and is superior to CT and ultrasound for suggesting the diagnosis of dermoid/epidermoid cyst.[7][8]
• Signal intensity varies with cyst contents:
  • T1-weighted: Intermediate to high signal; fat-containing cysts show T1 hyperintensity that suppresses on fat-saturated sequences (reported specificity approaching 100%).[30][31]
  • T2-weighted: Variable signal — typically heterogeneously hyperintense; keratinous debris may produce areas of low signal.[31][32]
• No internal enhancement after gadolinium administration.[31][33]
• A "sack of marbles" appearance (multiple small cysts within a larger cyst) has been described in dermoid cysts at other sites and may occasionally be seen in large oral lesions.[31]
• Diffusion-weighted imaging (DWI) can differentiate dermoid cysts from thyroglossal duct cysts: dermoid cysts show lower ADC values (mean ~1.5 × 10⁻³ mm²/s) compared with thyroglossal duct cysts (~2.2 × 10⁻³ mm²/s).[34]

Ultrasound

• Dermoid cysts appear as well-circumscribed, hypoechoic, heterogeneous masses with posterior acoustic enhancement.[35]
• Ultrasound is useful for initial assessment and can distinguish cystic from solid lesions, but it is less reliable than MRI for specific diagnosis; ranula was the most common misdiagnosis on imaging in one pediatric series.[7][35]

Dermoid cysts of the floor of the mouth must be distinguished from other midline or paramedian cystic masses in the sublingual and submental spaces. Imaging alone is frequently insufficient for definitive diagnosis; in one 20-year pediatric series, only 17% of sublingual dermoid/epidermoid cysts were correctly diagnosed preoperatively.[7]

The highest-risk diagnostic pitfall is misidentification as a ranula or lymphatic malformation, which may lead to inappropriate treatment such as marsupialization or sclerotherapy rather than definitive excision.[7] When imaging is equivocal, MRI with DWI and fat-saturation sequences provides the best preoperative characterization.[7][34]

Microscopic features

• Epithelial lining: Keratinized stratified squamous epithelium is present in all variants.[1][3]
• Adnexal structures (true dermoid): Sebaceous glands are the most common adnexal element (~81% of craniofacial dermoid cysts), followed by hair follicles; eccrine (sweat) glands are less frequent.[3]
• Cyst contents: Laminated keratinous material, sebaceous secretions, and hair shafts produce the characteristic thick, cheesy or doughy intraluminal material.[3][4]
• Fibrous capsule: Dense connective tissue; chronic inflammatory infiltrate may be present, particularly if prior rupture has occurred.[1][22]

Histologic variants

• Epidermoid variant: Squamous epithelial lining without adnexal structures.[1][5]
• Dermoid variant: Squamous lining plus skin adnexa (sebaceous glands, hair follicles, sweat glands).[1][3]
• Teratoid variant: Contains tissues from all three germ layers (ectoderm, mesoderm, endoderm), such as respiratory or gastrointestinal epithelium, muscle, cartilage, or bone.[4][5][14]

Unusual findings

• Gut epithelium (7%) and respiratory epithelium (14%) have been documented in oral dermoid cysts.[1]
• Pacini (lamellar) corpuscles, melanin pigmentation, and multinucleated giant cell reaction to extruded keratin are occasionally observed.[1]
• Chronic giant cell reaction to hair and keratin occurs in approximately 23–38% of ruptured or previously traumatized cysts.[22]

Radiologic–pathologic correlation

The heterogeneous density or signal seen on CT/MRI corresponds to the mixture of keratinous debris, lipid from sebaceous secretions, and hair within the cyst lumen. Fat-density areas on CT and T1-hyperintense foci on MRI reflect the sebaceous component, while solid-appearing areas correspond to compacted keratin.[4][30] The epidermoid variant, lacking sebaceous material, tends to show more homogeneous fluid-like signal.[37]

Workup and referral

• Clinical and bimanual examination to localize the mass relative to the mylohyoid muscle.[18][24]
• Cross-sectional imaging (MRI preferred; CT acceptable) to confirm cystic nature, delineate extent, and plan surgical approach.[7][8]
• Referral to oral and maxillofacial surgery or otolaryngology–head and neck surgery for definitive management.[2][12]

Surgical treatment

• Complete surgical excision is the standard of care and is curative.[2][12][13]
• Surgical approach is determined by the relationship to the mylohyoid muscle:[18]
  • Sublingual (supramylohyoid): transoral/intraoral approach
  • Submental (inframylohyoid): transcervical approach, or transoral with endoscopic assistance
  • Large or dumbbell-shaped cysts crossing the mylohyoid may require a combined intraoral–extraoral approach[18][19]
• Transoral excision offers shorter operative time and superior cosmetic satisfaction compared with transcervical excision.[28]
• Marsupialization has been described for very large cysts to reduce size and minimize risk to adjacent vital structures, though it is not standard.[20]

Recurrence and prognosis

• Recurrence after complete excision is rare. Multiple case series report 0% recurrence over follow-up periods averaging 5–6 years.[12][13]
• Incomplete excision is the primary risk factor for recurrence; in one head and neck series, 2 of 21 surgically treated patients (9.5%) recurred, both successfully managed with re-excision.[2]
• No malignant transformation has been reported for oral dermoid cysts.[1][2]
• Prognosis is excellent; the lesion is benign with no systemic implications.[12][13]

Pregnancy

Rapid enlargement of sublingual dermoid cysts during pregnancy has been documented, potentially causing dysphagia and respiratory compromise. Elective excision before conception has been recommended for known sublingual dermoid cysts in women of childbearing age.[21]

Neonatal and pediatric considerations

• Floor-of-mouth dermoid cysts presenting in neonates may cause feeding difficulty or airway obstruction, warranting early surgical intervention.[19]
• Sublingual dermoid/epidermoid cysts in children are frequently misdiagnosed as ranulas or lymphatic malformations; MRI is the most reliable imaging modality for suggesting the correct diagnosis preoperatively.[7]