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Picture Quiz Case history A 24 year old woman was found to have a 3 cm mass at the base of the tongue (figure) at intubation before a gynaecological procedure. She had been unaware of the mass and was asymptomatic.
Questions (1) What is the diagnosis? Answers (1) Lingual thyroid. A lingual thyroid typically appears as a raised pink mass in the posterior third of the tongue. The differential diagnosis is any cause of a posterior swelling in the oral cavity. Congenital masses are rare in this location, but occasionally haemangiomas and cystic hygromas may present as swellings in the mouth. Acquired swellings include hypertrophy of the lingual tonsil, abscess, foreign body, and retention cysts - submucosal accumulations of mucus caused by disruption of the duct system of minor salivary glands. Retention cysts present as smooth, cystic swellings, most commonly located on the lower lip and floor of the mouth, but can occur anywhere in the oral cavity. Neoplastic causes include benign and malignant tumours arising from the anatomical structures of the oropharynx, including the base of the tongue, tonsils, pharyngeal walls, and soft palate. The tongue is a common location for papillomas - soft, pedunculated lesions caused by the human papillomavirus. Other benign neoplasms include fibromas, neurofibromas, and benign minor salivary gland tumours (pleomorphic adenomas). Squamous cell carcinoma is the most common malignant neoplasm of the oropharynx. Discussion Lingual thyroid is a mass of ectopic thyroid tissue, located in the base of the tongue, caused by a developmental anomaly of the descent of the thyroid gland. The thyroid gland originates from the median bud of the pharynx as an endodermal diverticulum during the third week of embryological development. The diverticulum migrates inferiorly as the thyroglossal duct and the caudal end becomes bilobed. By the seventh week, the gland reaches its final pretracheal position and the thyroglossal tract is obliterated. The origin of the tract remains as a pit on the base of the tongue called the foramen caecum. Ectopic thyroid tissue may be deposited in any position along the tract and can be mistaken for a thyroglossal cyst. Lingual thyroid is rare and is found in approximately 1 in 100 000 people. It is more common in women, with a female to male ratio of 4:1. Onset of symptoms often coincides with puberty, pregnancy, or the menopause, when raised levels of thyroid stimulating hormone (TSH) cause hypertrophy of the gland. Initial evaluation includes a thorough head and neck examination. Endoscopic examination of the upper airway is necessary to determine gland size and airway patency and to exclude other possible diagnoses. Palpation of the neck and ultrasound scanning are performed to check for presence of thyroid tissue in the normal position. Affected individuals have no other thyroid tissue in more than 70% of cases. Thyroid function tests often demonstrate normal (euthyroid) to underactive (hypothyroid) gland function, with normal to decreased levels of thyroxine (T4) and tri-iodothyronine (T3) and raised levels of TSH. The uptake by the thyroid of a low dose of radiolabelled technetium (99mTc) is diagnostic of lingual thyroid, typically showing radionuclide activity in the tongue base with no activity in the normal position in the neck.1 Using thyroxine to suppress TSH is the mainstay of conservative management, aiming to control gland size and local symptoms. Surgery is indicated when symptoms deteriorate despite medical treatment. Absolute indications are severe, repeated haemorrhage, dysphagia preventing adequate oral intake, and significant airway compromise. Thyroid ablation with radioactive iodine is an alternative to surgery and is usually reserved for unfit patients or those who refuse surgical intervention. This picture quiz was prepared by Lucy Wales, lecturer in surgery, and Peter Clarke, consultant ear nose and throat surgeon, Charing Cross Hospital, London W6 8RF
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