Introduction
Ectopic thyroid is an uncommon embryological abnormality characterised by the presence of thyroid tissue in a site other than its usual pre-tracheal location.Reference Yang and Hong1 Ectopic thyroid tissue results from developmental defects at early stages of thyroid gland embryogenesis, during its passage from the floor of the primitive foregut to its final pre-tracheal position.Reference Noussios, Anagnostis, Goulis, Lappas and Natsis2 Lingual thyroids have an incidence of 1:3000 to 1:10 000.Reference Zackaria, Chisholm, Tolley, Rice and Chhatwani3
Thyroid scintigraphy utilising 99mTc-pertechnetate disodium or 123I plays a vital role in diagnosing this disorder.Reference Noussios, Anagnostis, Goulis, Lappas and Natsis2 Head and neck imaging using single photon emission computed tomography and the newly introduced hybrid of single photon emission computed tomography plus standard computed tomography (CT) enables three-dimensional (3D) image acquisition and display, while at the same time improving imaging interpretation and thyroid scintigraphy accuracy in patients with suspected ectopic thyroid tissue.
Here, we present a rare case of a lingual thyroid detected using a hybrid of single photon emission computed tomography and standard CT in a young woman with hypothyroidism.
Case report
Following screening for autoimmune thyroid disorders during pregnancy,Reference Horacek, Spitalnikova, Dlabalova, Malirova, Vizda and Svilias4 a 29-year-old woman in the 13th gestational week was referred to our endocrine clinic due to an increased level of thyroid-stimulating hormone (TSH; also know as thyrotropin).
Further investigations confirmed an elevated TSH concentration (7.35 mU/l; reference range, 0.15–5 mU/l) together with a low to normal level of free thyroxine (T4; 11.58 pmol/l; reference range, 11–25 pmol/l) and a normal free tri-iodothyronine level (T3; 3.15 pmol/l; reference range, 2.5–5.8 pmol/l). The level of antibodies against thyroid peroxidase was not elevated.
Ultrasonography of the anterior neck revealed the absence of thyroid tissue in the usual location.
There were no clinical symptoms or signs of hypothyroidism.
Levothyroxine was administered (50 µg per day, later increased to 75 µg per day) to treat the patient's subclinical hypothyroidism during her pregnancy.
After a full-term pregnancy, she gave birth to a healthy son.
Three months later, the patient's thyroid status was normal (TSH, 3.97 mU/l; free T4, 15.68 pmol/l; free T3, 4.08 pmol/l), following ongoing thyroxine replacement therapy. Although her thyroid peroxidase antibody level was retested and was again found to be normal, post-partum thyroiditis was suspected due to elevation of the serum thyroglobulin concentration (to more than twice the normal range). Indeed, the patient's thyroxine dose had to be further increased, to 125 µg per day, during follow up.
When the patient stopped breast-feeding (approximately 12 months after delivery), we performed 99mTc-pertechnetate disodium scintigraphy to locate her endogenous source of thyroid hormones. Whole-body scintigraphy and zoomed static head and neck scintigraphy were performed 15 minutes after administering 99mTc-pertechnetate disodium (200 MBq) intravenously. An area of pathological 99mTc-pertechnetate uptake was observed in the oral region, with no uptake in the normal anatomical location of the thyroid gland.
To improve 3D visualisation of the area of increased activity, we also used a hybrid of single photon emission computed tomography plus standard CT. A rotating, dual-head, hybrid single photon emission computed tomography and standard CT scanner (Infinia Hawkey 4; GE, Fairfield, Connecticut, USA) with infrared body contouring and a large field of view was used. The images were evaluated using Xeleris processing systems (GE). Using this system, we detected 99mTc-pertechnetate uptake in the tongue, indicating ectopic thyroid tissue (Figure 1).
Fig. 1 Head and neck imaging (sagittal views) using a hybrid of single photon emission computed tomography and standard computed tomography (CT): (a) standard CT, (b) single photon emission computed tomography with attenuation correction, (c) fusion single photon emission computed tomography plus standard CT, and (d) single photon emission computed tomography without attenuation correction. Uptake of 99mTc-pertechnetate disodium in the ectopic lingual thyroid tissue is seen (plain arrows). A = anterior; P = posterior
Discussion
Our finding of a lingual ectopic thyroid in a young woman, identified using 99mTc-pertechnetate disodium thyroid scintigraphy and a hybrid of single photon emission computed tomography and standard CT, is similar to other, previously reported cases. Deshmukh et al. Reference Deshmukh, Katna, Patil, Chaukar, Basu and D'Cruz5 reported a 44-year-old patient with ectopic thyroid tissue in the submandibular space. Ulug et al. Reference Ulug, Ulubil and Alagol6 described a case of dual ectopic thyroids in the lingual and infrahyoid areas in a 20-year-old woman who had no thyroid gland in its normal anatomical location. Eli et al. Reference Eli, Marnane, Peter and Winter7 reported a case of ectopic thyroid tissue presenting as a submandibular mass in a patient with hyperthyroidism. Zackaria et al. Reference Zackaria, Chisholm, Tolley, Rice and Chhatwani3 presented a case of multinodular lingual goitre in a 66-year-old woman with dysphagia, in whom a previously silent lingual thyroid had undergone multinodular change, causing the reported symptoms; the goitre was excised. Gorur et al. Reference Gorur, Isgoren, Tan, Utkan, Demir and Berk8 reported a patient with an ectopic mediastinal goitre and Graves' disease. Pelizzo el al.Reference Pelizzo, Torresan, Grassetto, Briani, Cristina Marzola and Rubello9 used ultrasound and 99mTc-pertechnetate disodium scintigraphy to detect the coexistence of submandibular ectopic thyroid tissue in the lateral neck with a normally located and functional thyroid gland, in a 54-year-old man with a 6-month history of a visible, asymptomatic swelling in the right submandibular region.
• Ectopic thyroid tissue is effectively detected by whole body 99mTc-pertechnetate scintigraphy
• A hybrid of single photon emission computed tomography plus standard computed tomography enables better three-dimensional imaging of head and neck ectopic thyroids
Conclusion
Whole body 99mTc-pertechnetate scintigraphy is an effective imaging modality for ectopic thyroid tissue in patients who have no thyroid gland in the normal anatomical location. In order to improve 3D visualisation of the ectopic thyroid, head and neck imaging using a hybrid of single photon emission computed tomography and standard CT is recommended.
Acknowledgements
This work was supported by the Czech Ministry of Health (research project code MZO 00179906).
