Choristomas

Choristoma is a mass composed of normal tissue in an abnormal location. It is a form of heterotopia. It differs from hamartoma, which is an abnormal excess of tissue native to the site, and from teratoma, which contains tissues from more than one germ layer. Choristomas are typically congenital, resulting from displaced embryonic cells during development. Rarely, they are thought to arise after trauma or surgical implantation of tissue.

Choristomas are categorized by the type of tissue involved. Reported histologies include osseous (bone) and cartilaginous tissue, pancreatic tissue, and other glandular or muscular tissues, located in sites where that tissue does not normally reside, such as the tongue, oral cavity, or other mucosal surfaces.

Clinical presentation varies with location. They may be asymptomatic and found incidentally or may form a mass that causes functional disturbance or cosmetic concerns. Imaging is often non-specific; definitive diagnosis relies on histopathology showing normal tissue in an ectopic setting.

Management is usually surgical excision when symptomatic or for diagnostic confirmation. Prognosis is excellent after removal, and recurrence is uncommon. Malignant transformation is not characteristic of choristomas, though rare associations with underlying syndromes have been described in a few cases.