Lingual Thyroid — ORE Part 1 MCQ

Correct answer: D — Lingual thyroid (ectopic thyroid tissue)

The diagnosis is lingual thyroid (ectopic thyroid tissue). This rare developmental anomaly results from failure of thyroid tissue to descend through the thyroglossal duct during embryogenesis, leaving it ectopically in the midline base of tongue. The clinical presentation—painless, firm, smooth, well-circumscribed 2 cm mass present since childhood with normal overlying mucosa—is classic for lingual thyroid. The MRI finding of a well-defined homogeneous mass within tongue muscle, without infiltrative features, is characteristic. Lingual thyroid is most common in young women and may be asymptomatic until discovered incidentally. Granular cell tumour is solitary and superficial, not typically at the tongue base. Lingual tonsil hypertrophy is lymphoid hyperplasia, not a discrete mass, and clinically distinguishable; it is a common misdiagnosis. Squamous cell carcinoma would show malignant imaging features (infiltration, irregular margins) and would not be painless for years. Haemangioma would demonstrate vascular enhancement and different clinical behavior. Definitive diagnosis combines clinical findings, MRI for anatomical definition, and thyroid scintigraphy (technetium-99m or iodine uptake) to confirm functioning ectopic thyroid tissue.

Reference: Lingual thyroid: the diagnostic value of magnetic resonance imaging. PubMed (2072027), 1991. https://pubmed.ncbi.nlm.nih.gov/2072027/; Ectopic Lingual Thyroid. PMC4393890, 2015. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4393890/