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Author: Dr David Veitch, Dermatology Registrar, Royal Infirmary of Edinburgh, Scotland. Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, November 2015.
Choristoma is a rare benign tumour consisting of microscopically normal tissue derived from germ cell layers foreign to that body site. Choristomas are classified according to their type of tissue. They sometimes arise within the skin or oral cavity, and can also occur in internal organs.
Choristoma may be diagnosed at any age from birth up until old age. Epidermal choristomas have all occurred in males. Most cases of lingual osseous choristoma have been reported in females in the third and fourth decade. Phakomatous choristoma and salivary gland choristoma tend to arise in newborns.
Choristoma is a developmental abnormality. For example, a dermoid cyst arises from epithelium trapped along lines of embryonic fusion. The reason they present late in life in some cases is unknown. One theory is that it may be due to chronic irritation.
Epidermal choristoma on the dorsum of the tongue most often presents as a brown to black pigmented macule of variable size (3–11 mm). The differential diagnosis of pigmented macular choristoma on the tongue includes congenital melanotic macule and melanocytic naevus.
Osseous choristoma presents as a pedunculated, painless hard lump on the dorsum of the tongue, posterior to the foramen caecum. Oral choristoma can also occur on the gingiva or buccal mucosa.
Phakomatous choristoma has similar appearance but arises around the orbit or eyelid region. Clinical concern may be of a rhabdomyosarcoma.
A choristoma in the auditory canal presents as a mass causing hearing loss and may predispose to infection.
Choristoma is usually excised.
The lesions are benign with little risk of malignant transformation. Recurrence rates after excision are extremely low.
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