Recent biomolecular studies have identified the bio-genetical mechanisms of thyroid morphogenesis and differentiation; this gives us the opportunity to understand thyroid malformative abnormalities due to morpho-genetical errors. These errors cause an abnormal dislocation of the primordial median rudimentary thyroid, determining the development of thyroid tissue in different districts (lingual, mediastinal ad also intracardiac). In some cases, for this same reason, due to these genetic errors, if the duct fails to obliterate, it may give rise to the development of a fistular passage (thyroglossal duct cyst). The thyroglossal duct cyst is the outcome of the persistence and of the cystic growth of the remnants of the thyroglossal tract    . Recently, specific follicular thyroid cell transcriptional factors have been identified which are responsible, selectively, for the thyroid genic expression of TTF-1, TTF-2 and PAX-8, each one of these genes is also expressed in stem cells and are different from the follicular thyroid cells, the association of these three factors is characteristic of the hormonogenetic thyroid cells    . The thyroglossal duct cyst is one of the most common congenital malformation cervical (about 70%), 50% of these cases appearing in patients aged 20 or younger and the prevalence of location of the cyst is along the midline (75%), in para-median position in the remaining 25%. The thyroglossal duct cyst papillary carcinoma incidence is about 1%. This neoplasia is characterized by a relatively non aggressive behavior with rare involvement of the thyroid gland and locoregional lymphnodes spread. Brentano, in 1911, defined the first carcinoma of the thyroglossal duct  . This carcinoma can appear during the childhood, but the peak incidence is between the forth and the fifth decades, females are affected slightly more often than males, with a 3:2 ratio  . The papillary hystotype is about 80% of all the thyroglossal carcinomas, followed by mixed folliculo-papillary carcinoma (8%), squamocellular carcinoma (6%) and the remaining 6% concerns Hurtle cells carcinoma, follicular carcinoma and anaplastic carcinoma    .
2. Case Report
A 40 years old woman presents before us with a 5 years’ history of a great anterior midline neck mass, enlarging during the last months. At the physical examination we can see an ovoidal mass, located in hyoid region, covered by normal skin, about 5 cm in diameter; palpation reveals a painless, mobile, non-tender, elastic mass. Ultrasound guided Fine Needle Aspiration Biopsy demonstrates that the lesion is arising, probably, in a thyroglossal duct, however some cytocariological abnormalityes are displayed in some foci, in particular, there is a moderate grade of anemacrocytosis with ground glass nuclei, worthy of further hystologic diagnostic deepening in order to reject a concomitant intracystic papillary carcinoma. A RMI, performed with and without paramagnetic contrast (Gd-DPTA), integrated by neck T1-weighted FAT-SAT acquisitions, shows cystic ovoidal lesion with regular border, located along the median cervico-anterior line of the neck below the hyoid bone, having transverse diameter about 3 cm long, and extending 6 cm, craniocaudally, hyperintense signalling on T2-weightened, omogeneous on T1-weightened, without mdc, acquisitions, insinuating itself inside the strap muscle in infrahyoidal region. Inside the lesion a solid nest is recognizable (at infra-hyoid epiglottic axial plane levels) developing in the median and paramedian right region, having maximum transverse diameter of about 13 mm and showing clear, marked enhancement after the administration of the mdc i.v. These RM findings are related to the presence of a large median cystic lesion in the neck: probably thyroglossal duct cyst with solid nucleus demonstrating clear enhancement after the administration of mdc i.v. This finding does not allow excluding that the lesion lies inside an ectopic remnant of thyroid tissue contained in a thyroglossal duct cyst. Some lymphnodes, moderately greater in number and in size, are present, bilaterally, at level I and II (Figure 1 and Figure 2). The patient, therefore, undergoes median cervicotomy
Figure 1. T1W, FAT SAT, lateral view, magnetic resonance image demonstrating the cystic ovoidal lesion located along the median anterior line of the neck below the hyoid bone, having tranverse diameter about 6 cm.
with removal of a portion of hyoid bone (Sistrunk’s Tecnique). The hystopathologic examination of the material obtained during surgery confirmed the presence of a smooth, 4 cm in diameter, adhering to a 1.5 cm portion of bone, cystic lesion whose wall and lumen contain neoplastic nests organized in papillary structures having nuclear pseudo-inclusions. Further, there is no evidence of hyoid bone infiltration. (Figure 3) The immunohystochemical examination with TTF-1, Cytocheratine, HBME-1 positivity and CD56 negativity in these neoplastic elements. This morphological description suggests a papillary carcinoma arising in a thyroglossal duct cyst (Figure 4 and Figure 5). The first year follow-up
Figure 2. T1W, axial view, magnetic resonance imaging of the neck shows anteromedial neck lesion with hyperintense signal. Inside the lesion a solid nest is recognizable developing in the median and a paramedian righ region having a transverse diameter of about 13 mm and shoving clear marked enhancement.
Figure 3. Papillary carcinoma evolving from a thyroglossal duct cyst. Cytocariological abnormalityes are visible in some foci, in particular, there is a moderate grade of anemacrocytosis with ground glass nuclei. (Stain: Hematoxylin & Eosin, original magnification × 10.)
Figure 4. The immunohystochemical examination has proved TTF-1, Cytocheratine, HBME-1 positivity and CD56 negativity in these neoplastic elements. This morphological description suggests a papillary carcinoma arising in a thyroglossal duct cyst (Stain: TTF-1; original magnification × 10).
Figure 5. Red: image demonstrating the cystic ovoidal lesion located along the median anterior line of the neck below the hyoid bone. Blue: inside the lesion a solid nest is recognizable developing in the median and paramedian right region. (Sketch performed by Paolo Gamba.)
includes the thyroglobulin level determination and a neck ecografic scan every 3 months. The patient has been following for two years without any metastasis.
The thyroglossal duct carcinoma management is greatly debated, particularly when thyroid gland is clinically normal. Some authors support the thesis that tyroglossal duct carcinoma originates within ectopic thyroid tissue, contained inside the cyst; other authors sustain the thesis of a metastasis deriving from the thyroid gland. Accordingly, the surgical approach too is greatly debated: some authors think adeguate the so called Sistrunk’s procedure when thyroid gland is normo-functioning. In 1920 Sistrunk  described a procedure to remove a thyroglossal cyst, which was based on the embriologic origin knowledge of the lesion. In this procedure the cyst, the median portion of hyoid bone and the tract of the thyroglossal duct, extending from the foramen cecum at the base of the tongue, to the hyoid bone, are removed in continuity. This technique is effective in low risk patients, according to: age, tumor dimension, prior thyroid diseases, capsular non-invasion, clinically and ultrasonographically normal lymphnodes, thyroid normo-conformation and normo-functioning    . Some authors, support the multifocality theory of the papillary carcinoma, prefer to perform total thyroidectomy with or without node dissection   . Here we support the pre-surgical work-up importance consisting of: neck MRI, neck ultrasound scan, ultrasonographically guided Fine Needle Aspiration    . Even if histology must give the definitive diagnosis, these pre-surgical examinations give the indications of a papillary neoplastic lesion, its localization, and its relations with the next structures and may direct the correct surgical strategy. Ouu case confirms the difficulty in distinguishing a primitive thyroglossal duct carcinoma from a synchronous metastatic papillary carcinoma of the thyroid. This dilemma often remains unresolved   . Long-term follow-up is necessary for patients with thyroid carcinoma arising in a TGDC  . In view of the frequent co-existence of thyroid cancer in these patients, we would recommend detailed thyroid evaluation and, eventually, total thyroidectomy at initial diagnosis of TGDC carcinoma (Table 1).
Our aim is to emphasize that significant attention must be paid to the pre-operative evaluation of the patient, the conclusions of the diagnostic phase can directly address towards the first choice surgery. The preoperative protocol we have done has given us the suspect of the presence of an intracystic thyroglossal duct papillary neoplasia, the hystopathologic examination of the material obtained during surgery confirmed, in fact, our pre-surgical diagnosis. So we have had the confirmation that ultrasonography, FNAB and MRI are essential to choose the surgical strategy and, at the same time, to achieve the definitive diagnosis of the lesion. Surgical Sistrunk’s procedure is adequate when thyroid gland is clinically and radiologically normal. Papillary thyroid carcinoma arising in thyroglossal duct cysts is a very rare malignant tumor. In spite of the multifocal character of several of our cases, their analysis showed that the
Table 1. Review cases of papillary carcinoma: case reports and review (PubMed-Indexed for MEDLINE).
TGDC: Thyroglossal duct cyst carcinoma.
prognosis in the vast majority of patients with TDC carcinoma is excellent. Moreover, we found no relation between outcome and surgical procedure.
We have informed and obtained the patient’ consent.
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