CASE REPORT Ectopic lingual thyroid - the role of imaging Abstract Ectopic thyroid tissue may be found throughout the migration course of the thyroid gland. Thyroid ectopy may be partial or total. The most common location of ectopic thyroid tissue is in the tongue base ( lingual thyroid). We discuss the computed tomography (CT) and radioisotope findings of a patient with ectopic lingual thyroid. Case report A Jl-year-old female presented with a history of feeling of a lump in the throat, but no dysphagia. Clinically a reddish lobulated soft tissue mass was seen at the base of the tongue. The patient was euthyroid. A clinical diagnosis of lingual thyroid was made. Five x Smm axial unenhanced and enhanced CT scans, of the neck and upper mediastinum, and coronalS x Srnrn enhanced CT scansof the nasopharynx and tongue base were per- formed on a General Electric Hi-speed Advantage CT Scanner. Ninety mliohexol 240 was administered intravenously as a bolus using a power injector at 2 rnlJsec . Technetium radioisotope (2.5 m CiTc04) scan using a Pieker Prism 2000 HP Gamma J Kew FFRad (D)SA. A Ahuja FRCR, P Scott FRCS (Otol)* Departments of Diagnostic Radiology and Organ Imaging and *Otorhlnolaryngology, Prince of Wales Hospital, sneun, Hong Kong 26 SAJOURNAL OF RADIOLOGY. November 1996 camera was also performed. A homo- genous hyperdense enhancing lobular mass, measuring 2.5 x 2 x 2cm, was noted at the base of the tongue and another lesion,meas- uring2x 1,Sx 1,Scmwas also noted anterior to the hyoid bone (Figures 1-3). Bilobular thyroid tissue was confirmed in the Figure 2: Axial enhanced CT scan demonstrating the intense enhancement of the lingual thyroid (arrow). topage 27 Ectopic lingual thyroid- the role of imaging from page 26 thyroglossal duct. It is believed that this mi- gration is achieved through the development of the body of the embryo caudad, and the cephalic progression of the tongue and phar- ynx. Early in the fifth week, the thyroglossal duct loses its lumen, while the foramen caecum remains at the tongue base The de- scent of the thyroid gland along the thyroglossal tract follows a vertical line in close contact but anterior to the hyoid bone and ends at the level of the upper trachea,leaving in 50% of cases, a midline pyrarnidallobe. It is easy to understand thyroid ectopy as a defec- tive descent of the gland. Total thyroid ectopy may be observed at various levels,suprahyoid location -lingual or sublingual, andinfrahyoid location, - prelaryngeal.' Lingual thyroid isthe most frequently encountered anomaly; ac- counting for approximately 90% of cases of total thyroidectopy/ In 70-80% oflingual thy- roid cases, the ectopic tissue is the only exist- ing thyroid tissue. The presence of a hyper- trophied ectopic thyroid gland may be asymp- tomatic or cause dysphonia and relative ob- struction of the upper respiratory and rr======='T7l0;'Pr======ïl gastrointestinal tracts. 3 The frequency is esti- matedtobe 1/4CXX)4 -l/lOOCXX).5Thepatho- logicalcondition develops most often between the third and fifth decade and there is a female predominance (7: 1) .4,6 Partial thyroid ectopy; that is,ectopic tissue in the presence of a thy- roid gland in its normal position may appear at various levels namely; suprahyoid location - lingual or sublingual, andinfrahyroid location -prelaryngeal, intra-tracheal, intra-oesophageal or intrathoradc. Complications include card- noma (3% papillary), but there isno increased incidence compared to normally positioned thyroid tissue. 6 1.....- --' The differential diagnosis ofa mass located in the foramen caecum area at the tongue base would include adenoma, thyroglossal cyst, angiomas, fibromas, chondromas, lymphangiomas, epithelioma, squamous cell carcinoma, adenoid cystic carcinoma, lymphoma and lymphosarcoma. 6 Irregular or inhomogenous contrast enhancement on cr Figure 3: Axial enhanced CT scan showing ectopic thyroid tissue (arrow) anterior to the hyoid bone (arrowhead). sublingual area on scintigraphy (Figure 4). No thyroid tissue was noted at the level of the thyroid cartilage or in the superior mediastinum on cr scan or sdntigraphy. Diagnosis: Ectopic lingual thyroid. AN Figure 4: Right lateral view of the thyroid Tc 04 scintigram demonstrating the ectopic thyroid tissue in the sublingual region (arrows). The asterix denotes the symphysis mentI. Discussion The thyroid primordium appears at the end of the third gestational week as a midline endodermic swelling in the ventral wall of the pharynx. Itpenetrates the underlying mescxlerm and starts its descent, connected to the tongue by a narrow epithelial channel, the SA JOURNAL OF RADIOLOGY· November 1996 would be expected in some of these lesions, and confusion with lingual thyroid could oc- cur. The diagnosis of a lingual thyroid how- ever can be confumedbythyroidisotopescan- ning (Technetium orIodine-l23). Scintigraphy is useful to confirm the presence of thyroid tissue, to assess other sites of ectopic thyroid tissue, and whether the ectopic tissue is the only thyroid tissue present. It does not how- ever have the spatial resolution of cr or MRI scanning, which can delineate the anatomical relations more predsely. Ultrasound may be used to evaluate the neck for ectopic thyroid tissue .A suspected lingualthyroid maybe seen as a softtissue mass at the base of the tongue with parenchymal characteristics similar to that of thyroid seen on ultrasound. 7 However, further confirma- tory tests, e.g. scintigraphy may need to be done. Summary Ectopic lingual thyroid is a congenital anomaly caused by failure of migration of the thyroid gland from the embryological pharyn- geal position to its usual location in the lower neck. The commonest location of ectopic thyroid is in the tongue base The diagnosis is usually made clinically;with radiology;usually thyroid radioisotope scan, as a confirmatory test. crscanandMRIareusefulin delineat- ingthe anatomical relations. References 1 Werz ML. Management of the undescended lingual and subhyoidglands Laryn~srope 1974;84:507-521 2 Weider OJ, Parker W. Lingual thyroid. All! Orol 1977;86:84 1- 848 3 Montgomery ML. Lingual thyroid: a comprehensive review. West f Suig I936;44:442-446. 4. Larochelle D, Arcand P,Belzile M, Gagnon NB. E topic thy- roid ti ue - 3 review of the literature. f Otola1)n11979;8[6]:523- 530 5 Haddad A, Freinkel S, Costom B, Shapiro R, TewftkT. Management of the undescended thyroid. J Otolaryngol 1006;15[6]373-376 6. Elprana D, Manni JJ, SmalsAGH. Lingual thyroid: case re- port and review of the literature. ORt Otorhinolaryngol Relat SjU; 1984;46: 147-152 7 Gaines PA, Ahuja A, Metreweli C. Radiological case of the season. Congenital conditions of the thyroid. loumol of the Hong KlmgMedicalAssociation 1990;42,[3]: 152-153.