Ectopic thyroid tissue in the parotid salivary gland.

Benign ectopic thyroid tissue within the parotid salivary gland is very rare. A 32-year-old woman presented with a slowly-growing, painless mass in the parotid region. The mass, which was clinically diagnosed as a parotid tumour, was found at surgery to be cystic in nature. Histological examination showed thyroid tissue with secondary changes in the cyst wall and colloid in the lumen. On iodine isotope scan, the thyroid gland was found in its normal location. The possible origin of the ectopic thyroid tissue in the parotid salivary gland could be due to a common evolution of the thyroid and parotid glands, a heteroplasia or a metaplasia.