Dysontogenic cysts are otherwise known as dermoid cysts. These cysts develop due to defective embryonic development. This cyst includes any cyst which are filled with sebum like material with evidence of presence of specialized skin derivatives.
Meyer's classification of Dysontogenic cysts of floor of mouth:
Meyer classified dysontogenic cysts of floor of mouth into 3 types, namely
Epidermoid cyst: is usually lined with stratified squamous epithelium without adnexal structures.
Dermoid cyst: is lined with stratified squamous epithelium with the presence of adnexal structures. These adnexal structures include sebaceous cysts, hair follicles and sweat glands.
Teratoid cyst: Features of teratoid cysts include the presence of lining squamous epithelium, respiratory epithelium, dermal appendages and distinct mesodermal components.
Eventhough dysontogenic cysts can occur anywhere in the body, about 10% of them occur in the floor of the oral cavity. Congenital cysts occuring in the infancy have also been reported.
These cysts can be congenital / acquired in nature.
Congenital cysts are derived from ectodermal differentiation of multipotential cells that could have been pinched off during the closure of the anterior neuropore. Commonly accepted theory explaining congenital cysts is that it is caused due to entrapment of midline ectodermal tissue during fusion of first and second branchial arches during the third week of gestation. Lateral dysontogenic cysts are said to arise from the first pharyngeal pouch or first branchial cleft.
Acquired dysontogenic cysts can be explaine by Baker's theory. According to Baker trauma is the commonest cause of acquired dysontogenic cysts. Trauma causes implantation of epithelial cells into deep tissues. These implanted tissues results in formation of cystic cavities filled with keratin.
These cysts should be differentiated from:
Obstructed wharton's duct
Thyroglossal tract cyst
Branchial cleft cyst
Enlarged submental glands
Prominent submental fat mass
Ultrasound examination will help in differentiating cystic from solid lesions. It ofcourse has the advantage of being easily available, cost effective and rapidly performed investigation.
MRI: Provides excellent soft tissue detail. It helps in differentiating mass from surrounding soft tissues. T2 weighted images of dysontogenic cysts shows hyperintense areas due to high proteinaceous content.
Complete excision of the mass is the ideal treatment modality. Almost all dysontogenic cysts of floor of the mouth can be approached through intraoral approach. All submental cysts should be approached through the neck. A cyst that has breached the floor of mouth musculature should ideally be approached through the neck.