MON-337 - An Unexpected Finding in A Patient with Congenital Hypothyroidism

Lingual thyroid (LT) is a rare congenital anomaly that arises from failure of the thyroid gland to migrate correctly during embryogenesis. During normal thyroid development, the thyroid originates around the 24th day of gestation at the foreman cecum and descends through the neck via the thyroglossal duct by weeks 5-7 to its final position in the upper trachea. LT occurs when the thyroglossal duct fails to migrate and remains at the base of the tongue. Most ectopic thyroid tissue is lingual, but can also occur in sublingual, thyroglossal, mediastinal, and cardiac regions. We present the case of a female with congenital hypothyroidism who was incidentally diagnosed with LT on imaging.

A 30-year-old female with a history of congenital hypothyroidism was admitted to the hospital for intravenous antibiotics after a diagnosis of pyelonephritis. During hospitalization, she developed transient neurological symptoms, prompting evaluation for stroke. Computed Tomography Angiography (CTA) of the head and neck showed no acute intracranial pathology. However, a well-circumscribed, enhancing 1.4 × 1.5 × 1.9 cm midline mass at the posterior base of the tongue with vascular connection to the left lingual artery was noted. Flexible laryngoscopy demonstrated a subtle submucosal midline protrusion at the base of the tongue. The patient denied dysphagia, dysphonia, odynophagia, and respiratory symptoms.

Ectopic thyroid tissue is rare with an estimated prevalence of one in 200,000 people in the general population, most commonly occurring in females. Despite this, LT remains clinically important as it can affect thyroid function and airway management. Clinical presentation varies from asymptomatic disease to dysphagia, dysphonia, hypothyroidism, or airway obstruction. This patient did not have symptoms associated with her LT and was diagnosed incidentally with imaging. Technetium-99m or Iodine-123 scintigraphy is the gold standard modality for detecting ectopic thyroid tissue. Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) are used to determine the precise anatomical location and distinguish thyroid tissue from surrounding structures. Confirmation with scintigraphy was discussed but not completed due to high clinical suspicion of LT in this patient with congenital hypothyroidism. Though congenital hypothyroidism is rare, affecting one in 2,000–4,000 newborns, thyroid dysgenesis accounts for about 65% of primary cases. Treatment depends on anatomical location, thyroid function, and symptom burden with medical therapy ideal for mild cases, as in this patient, and surgical intervention for airway compromise.

LT is a rare embryologic anomaly that should be considered in patients with lingual masses or unexplained upper airway symptoms, especially those with congenital hypothyroidism. Proper diagnosis guides management and allows for monitoring of complications.

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