Prevalence of Thyroglossal Duct Cyst Carcinoma in Adults Having Surgery for Thyroglossal Duct Cysts

Abstract

Thyroglossal duct cyst (TGDcyst) is the most common developmental abnormality of the thyroid gland (1). It usually presents as an asymptomatic, soft swelling in the midline and has characteristic ultrasound features. TGDcysts are usually benign lesions but a few cases of TGDcyst carcinoma (TGDcyst-Ca), approximately 250, have been reported (2). The data regarding the prevalence of TGDcyst-Ca in adults with clinically evident TGDcysts is sparse (3). In an attempt to estimate this, at least for patients with TGDcysts that demanded intervention, we carried out a retrospective review of the patients in our hospital who underwent surgical excision of TGDcysts between 2001 and 2011. Overall there were 23 patients who were surgically treated for TGDcysts and these were either large or rapidly increasing in size TGDcysts. Among them, there were three patients with TGDcyst-Ca. The first patient was a 37-year-old woman who in October 2001 was diagnosed with a 20-mm papillary thyroid carcinoma (PTC) within a TGDcyst (pT3N0Mx). The diagnosis was based on histopathology following surgical excision of the cyst by Sistrunk procedure. A total thyroidectomy (tTx) was subsequently performed and the thyroid itself was free of PTC. Following thyroid removal, because of persistently elevated recombinant human thyrotropin (rhTSH)-stimulated serum thyroglobulin (Tg), she received five treatments with I (RAI) for a cumulative dose of 15.91 GBq, between 2002 and 2009. She was prepared for these treatments with rhTSH. PostRAI whole body scans (WBS) revealed persistent low uptake in the left hemithorax. She declined further RAI treatments. The second patient was a 42-year-old man who underwent Sistrunk surgical excision of a cystic lesion of the neck in November 2001. Histological examination revealed a 14-mm PTC within a TGDcyst. It infiltrated surrounding tissues (pT3N0Mx). In March 2002, following tTx, a 3-mm PTC was found in the left thyroid lobe, and a second 1-mm PTC focus in the contralateral lobe (pT1bN0Mx). Six months after tTx, 3.7 GBq of RAI with rhTSH preparation was administered. The post-RAI WBS was negative and serum Tg concentrations after rhTSH administration were undetectable. The third patient was a 21-year-old woman underwent surgical excision of a TGDcyst by Sistrunk procedure in March of 2010. Histopathology showed a follicular variant of PTC within the TGDcyst (pT1N0Mx). A tTx was subsequently performed and no malignancies were noted in the thyroid gland. She was treated with 4.5 GBq RAI and serum Tg concentrations after rhTSH stimulation were consistently undetectable. In our series of 23 patients who had surgery for TGDcyst, the prevalence of TGDcyst-Ca was 13%. A similar study by Patel et al. (3) of patients who had surgery for TGDcyst at a large cancer center obtained a prevalence of 14%. In our small series of three patients with TGDcyst-Ca, the thyroid gland was free of PTC in two patients. This supports the hypothesis that PTC can arise from ectopic thyroid tissue, but can remain confined to its site of origin. None of the patients with TGDcyst-Ca in our series had follicular thyroid carcinoma, squamous cell carcinoma, Hurthle cell carcinoma, or anaplastic carcinoma. This is consistent with other reports indicating that PTC is the most common cancer to occur in TGDcysts but these other tumors have also been reported (1). There is considerable controversy regarding the role of thyroidectomy in the management of TGDcyst-Ca (4). We believe that tTx should be performed on all patients in whom TGDcyst-Ca is confirmed by histopathology of the TGDcyst specimen in order to rule out occult thyroid carcinomas that might have metastasized to the TGDC, even though it is evident that not all TGDcyst-Ca are associated with carcinoma within the thyroid gland itself. Moreover, the prognosis of TGDcyst-Ca is generally good. A very large prospective study would be needed to adequately address this issue. Although all three of our patients received radioactive iodine ablation the value of this treatment is unclear; future guidelines should address this issue. In summary, most patients who present with a large or clearly growing TGDcyst have a good prognosis, not only because most such lesions do not harbor cancer, but also because in many of them who do harbor cancer, this is confined to the TGDcyst. Nevertheless, we advocate that such lesions have prompt surgical treatment.