Lingual Thyroid

A 52-year-old female presents with an enlarging painless lump in her mouth. There is resultant dysphagia with concurrent lethargy and weight gain. Thyroid function test confirms hypothyroidism. Thyroid ultrasound fails to locate the thyroid gland in the neck. There is no history of previous thyroid surgery.

Pre and Post contrast Ct base of skull to clavicle was requested. On Pre contrast acquisition, there is a well-circumscribed hyperdense mass arising from the base of the tongue. It resembles thyroid tissue due to its Iodine content (Figure 1). There is no associated haemorrhage or calcification.

Post-contrast administration, the mass enhances avidly and homogeneously. There is no associated cysts or neovascularity. The mass measures 2,1 cm x 1,7cm x 2,3 cm. (Figure 2)There is no invasion of adjacent structures. No thyroid gland is present in the pretrachael region. (Figure 3)

Background

During the 3^rd to 9^th week of gestation, the thyroid gland descends from the Foramen Cecum to its normal pretrachael location. Thyroid ectopia is attributed to failure of caudal migration along the course of the thyroglossal duct. Lingual thyroid accounts for 90% of ectopic thyroid cases. There is a female predominance.

Clinical Perspective

The majority of lingual thyroids are asymptomatic and diagnosed incidentally. The symptomatic subset presents with hypothyroidism, a reddish oral mass or compressive symptoms such as dysphagia or sleep apnoea. The ectopic thyroid enlarges proportionately as untreated hypothyroidism progresses. Rarely, malignancy may develop within the lingual thyroid.

Imaging Perspective

The modalities which maybe employed are ultrasound, computed tomography, magnetic resonance imaging or nuclear medicine scintigraphy utilising Iodine-123 or Tc–99m-pertechnetate tracers.

Ultrasound is cost-effective and does not generate radiation. Therefore, ultrasound is the first-line investigation. A KEY IMAGING FINDING is the absence of thyroid gland at its expected locus.

IMAGING PEARL:  On non-contrast CT base of skull to clavicles, the lingual thyroid is hyperdense due to its Iodine content and morphologically resembles thyroid tissue.

Nuclear medicine Scintigraphy provides a functional dimension. It confirms tracer uptake by active thyroid tissue at the base of the tongue.

A Guided Fine needle aspirate cytologically verifies thyroid tissue. However, invasive procedures can be avoided due to the accuracy of imaging.

Treatment

Asymptomatic euthyroid cases do not require active treatment. Follow up is sufficient.

Non-Surgical Treatment constitutes Hormone therapy to manage hypothyroidism.

Radioactive Ablation and surgical excision is avoided as it may trigger profound irreversible hypothyroidism.

Outcome

Treatment for hypothyroidism was instituted. The lingual thyroid decreased in size as the patient responded to therapy. Symptoms resolved once Euthyroid state was achieved.