July 23, 2020
A 15-year-old boy with a 3-month history of painless, progressively enlarging mass on floor of the mouth on the right side
Sublingual Dermoid Cyst
- Background:
- Dermoid cysts are benign lesions arising from stem cells that undergo ectodermal differentiation. The cyst lining is composed of keratinizing squamous epithelium and typically contains skin appendages such as sebaceous glands and hair follicles.
- Nearly 34% of dermoid cysts are found in the head and neck, of which 6.5% are located at the floor of the mouth.
- Clinical Presentation:
- Dermoid sublingual cysts tend to manifest in the second or third decade, usually as asymptomatic masses.
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If the cyst reaches a large size, it may produce complications such as dysphagia, dysphonia, and dyspnea.
- Key Diagnostic Features:
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Imaging reveals a unilocular, well-defined cystic lesion on the anterior aspect of the floor of the mouth. They may have intracystic floating corpuscles, known as a “sack of marbles” sign, represented as echogenic nodules on US, hypodensity on CT scans and hyper/isointensity on T1- and T2-weighted sequences depending on the lipid component, immersed in T2-hyperintense fluid content. This appearance is pathognomonic for sublingual dermoid cysts.
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- Differential Diagnoses:
- Epidermoid cysts: Contain only epithelial elements and consequently do not show such heterogeneity on MRI. Epidermoid cysts also lack intralesional fat elements, and the cystic components show restriction at diffusion imaging.
- Lymphatic malformations: Usually are multicompartmental and may be unilocular, often exhibiting uniform high T2 signal on MRI, or multilocular, presenting with enhancing septa or fluid-fluid levels.
- Ranulas: Retention cysts mostly arising from a sublingual gland that may mimic dermoid cysts but do not exhibit internal corpuscles. They demonstrate a characteristic beak toward the sublingual space (tail sign).
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Branchial cleft cysts: Can be differentiated from sublingual dermoid by their localization. First branchial cleft cysts typically appear near the auricle and second branchial cleft cysts are found along the anterior border of the sternocleidomastoid muscle.
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Thyroglossal duct cysts: Midline structures, typically at the posterior tongue root, that are usually homogeneous, without complex elements inside.
- Treatment:
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The treatment is surgical; the approach can be either intraoral or extraoral, depending on the localization and size of the mass.
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Because of dense material inside the cyst, percutaneous fine-needle aspiration is not recommended.
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