The Answer

ectopic lingual thyroid

Discussion

This rare embryological anomaly originates from a failure of descent of the normal thyroid. The most common site of an ectopic lingual thyroid is the base of the tongue at the foramen caecum. This anomaly is more common in women.
These are usually asymptomatic, and in a majority of cases, there is no normal thyroid in the expected location of the thyroid bed. This may be the only functioning thyroid parenchyma, and will follow normal thyroid on imaging studies, with high density on CT, and avid uptake on nuclear medicine Tc-99m-pertechnetate scans.

References

1. Benhammou A, Bencheikh R, Benbouzid MA, Boulaich M, Essakali L, Kzadri M. Ectopic lingual thyroid. B-Ent. 2006;2(3):121-122.
2. Toso A, Colombani F, Averono G, Aluffi P, Pia F. Lingual thyroid causing dysphagia and dyspnoea. Case reports and review of the literature. Acta Otorhinolaryngol Ital. Aug 2009;29(4):213-217.
3. Mussak EN, Kacker A. Surgical and medical management of midline ectopic thyroid. Otolaryngol Head Neck Surg. Jun 2007;136(6):870-872.