Lingual thyroid is a developmental anomaly of the thyroid gland. It is a form of ectopic thyroid tissue located in the midline at the base of the tongue, resulting from disruptions during the embryological development of the thyroid. Lingual thyroid is the most common form of ectopic thyroid tissue and can be found anywhere between the circumvallate papillae and the epiglottis (1). Although it is a rare anomaly, it accounts for 90% of ectopic thyroid cases outside the pyramidal lobe. Additionally, it is the most frequent cause of benign neoplasms at the base of the tongue (2). The first reported case of lingual thyroid was described by Hickman in 1869 (3). Given its rarity in general surgical practice, we aim to discuss this ectopic condition due to its association with obstruction and dysphagia.
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Case Report
A 29-year-old female presented with complaints of bad breath, a sensation of obstruction in the throat, shortness of breath, difficulty swallowing, and occasional throat bleeding. Clinical examination revealed a 2 cm round mass with a base attached to the left side of the tongue base, covered with white fibrin. Neck CT showed a soft tissue mass measuring 15x16x15 mm in the oropharynx connected to the tongue base, with an adjacent area of intense contrast uptake measuring 15x10 mm. MRI revealed a 20x15x18 mm encapsulated mass in the midline, significantly narrowing the airway and attached to the tongue base. Thyroid hormone levels were FT3: 1.65 pg/ml (1.45-3.48), FT4: 0.67 ng/ml (0.8-1.9), TSH: >75 uIU/ml (0.4-4). Scintigraphy showed no activity in the normal thyroid location in the midline of the neck but intense Tc-99m pertechnetate uptake in the oropharynx, consistent with lingual thyroid. The patient was rendered euthyroid with levothyroxine treatment before undergoing surgery. The lingual thyroid was excised transorally using plasmacision (GirusENT, USA). Pathological examination revealed diffuse hyperplasia and ulceration with granulation tissue on the surface epithelium. Postoperative scintigraphy showed no activity in the oropharynx or elsewhere. The patient was discharged without complications and started on postoperative levothyroxine therapy.
Discussion
Embryologically, the thyroid gland develops from an endodermal diverticulum between the first and second pharyngeal pouches, with the opening of the diverticulum located at the foramen cecum at the tongue base. Ectopic thyroid tissue arises from incomplete migration during its descent from the foramen cecum to its normal position in the neck by the 7th week of embryonic life. Ectopic thyroid tissue usually develops between the foramen cecum and the thyroid gland's normal location, but it can also occur in the mediastinum due to its embryological relationship with the heart (4).
Although rare, lingual thyroid accounts for 90% of ectopic thyroid cases outside the pyramidal lobe (2). Its incidence ranges between 1/3000 and 1/100,000. In 70% of cases, the lingual thyroid represents the only thyroid tissue. Approximately 400 cases have been reported in the literature for various reasons (5). It is more common in women and can occur at any age, peaking in the second decade. Hypothyroidism is reported in 14.5-33% of cases (6). It becomes symptomatic during periods of increased thyroid hormone demand, such as puberty and pregnancy, due to an increase in the volume of the lingual thyroid. Our patient, a woman in her fourth decade, presented with symptoms and had hypothyroidism.
Lingual thyroid typically appears as a single, round, vascularized soft tissue mass at the tongue base. If the mass bleeds, surface ulcerations or blood clots may be visible. In our case, clinical examination revealed a round 2 cm mass covered with white fibrin at the left side of the tongue base. Pathological examination of the excised thyroid showed diffuse hyperplasia and surface ulceration.
Radiological imaging modalities such as neck ultrasound, CT, MRI, and Tc-99m thyroid scintigraphy can be used for diagnosis. Ultrasound differentiates normal thyroid tissue from ectopic thyroid tissue and identifies cysts or nodules. CT and MRI provide clear details about ectopic thyroid tissue's location, size, and relationship with surrounding tissues (7,8). Scintigraphy with Tc-99m pertechnetate is the most accurate method to confirm thyroid tissue and assess the presence of functional thyroid tissue in normal locations (9). Differential diagnosis includes lingual tonsillitis, submandibular gland neoplasms, adenomas, fibromas, thyroglossal duct cysts, and malignancies of the tongue base (10).
Based on clinical, radiological, and laboratory findings, ectopic thyroid tissue was initially suspected. Treatment is considered when lingual thyroid becomes symptomatic. Indications for surgery include severe or recurrent bleeding, growth causing dysphagia, significant airway obstruction, and suspicion of malignancy. Surgical approaches include transoral, transmandibular, or transcervical lateral pharyngotomy (6,10). The transoral approach provides limited visualization. Bleeding is a significant concern, and ligation of the lingual artery can lead to necrosis of the tongue. However, the transoral approach avoids cosmetic deformities, postoperative neck infections, and fistulas. In contrast, external approaches offer better visualization but carry risks of infection, scar formation, and fistula development from the mouth to the neck (11). Due to the patient's young age and the thyroid gland's oropharyngeal location, we opted for a transoral approach.
In conclusion, lingual thyroid is a rare but significant pathology that should be considered in cases of hypothyroidism with dysphagia or airway obstruction. Symptoms improve quickly following the appropriate surgical procedure. Preoperative hypothyroidism should be treated in affected patients.
