Discussion
Lingual thyroid represents 90% of all cases of ectopic thyroid2,4. Hickmann recorded the first case of lingual thyroid in 18695. It is a rare embryogenic anomaly and results from failure of descend of thyroid from foramen caecum to its normal entopic prelaryngeal location6. The prevalence rate varies from 1:100,000 to 1:300,000(3). Female to male ratio ranges from 3:1 to 7:17. Lingual thyroid may be asymptomatic, incidentally discovered during clinical examination. It may present as a sooth lobulated mass in throat. The mass can cause obstruction of oropharynx and cause dysphagia, foreign body sensation in throat, dyspnoea, stridor, snoring etc8. Other symptoms might result from thyroid insufficiency. Features of hypothyroidism like weight gain, tiredness, menstrual irregularity, loss of appetite maybe present. Very rarely, lingual thyroid can undergo malignant transformation. Malignancy in entopic thyroid gland is mostly papillary carcinoma. Contrary to it, malignancy in ectopic thyroid gland is mostly follicular carcinoma2. The malignant mass presents as an ulcerative, rapidly growing mass in throat. Imaging is the modality of choice for diagnosis. Ultrasonography is the most convenient and easy one. It has no radiation. The most consistent finding is absence of thyroid gland in its entopic location. Thyroid tissue may be found along the path of descend of thyroid gland. Sometimes the gland maybe hypoplastic and not visualized in ultrasound9. CT is another modality but often avoided due to radiation. In non-contrast CT, thyroid gland is hyperdense and show homogeneous post contrast enhancement10. Lingual thyroid is seen at base of tongue, between sulcus terminalis and epiglottis. In MRI, lingual thyroid is seen as a non-invasive mass in base of tongue. Thyroid tissue is iso to hyperintense in T1 weighted image. In T2 weighted image, thyroid can be hypo to iso to hyperintense. In post contrast images, homogeneous enhancement is seen6. Scintigraphy with Tc-99m is another reliable diagnostic tool. Absence of isotope uptake in cervical region and presence of uptake in oropharynx points towards diagnosis of lingual thyroid11.
Outcome : The patient was given levothyroxine suppression therapy. Patient was followed after 1 month. The mass was markedly reduced in size. The patient was euthyroid. Maintenance done of levothyroxine was given and regular follow up was done. Other therapeutic options can be surgical removal and radioactive iodine ablation11. Surgery is reserved for patients with severe symptoms refractory to medicines. Radioactive iodine is avoided in children and young adults11.