Case report: ectopic papillary thyroid carcinoma found in the midline of the hyoid bone and cervical lymph nodes, no thyroid lesions

Introduction

Ectopic thyroid tissue (ETT) refers to thyroid tissue located outside its normal anatomical position, such as in the second to fourth tracheal cartilages. ETT primarily occurs due to embryonic thyroid germ incomplete descent during embryonic development, which can occur at the base of the tongue, neck, pulmonary even other locations (1). The risk of malignant transformation in ETT is extremely, and the associated risk factors are not yet known.

We report the case of a 30-year-old woman with papillary thyroid metastases at the midline of the hyoid bone and metastases in the lateral cervical lymph nodes, but no thyroid lesions. We present this article in accordance with the CARE reporting checklist (available at https://acr.amegroups.com/article/view/10.21037/acr-2025-130/rc).

Case presentation

A 30-year-old woman attended in Guangdong Provincial Hospital of Traditional Chinese Medicine complaining of a benign mass on the left side of her neck, which had been present for more than 10 years, and an anterior neck mass, which had been present for one year. The patient reported no progressive enlargement, pain, dysphagia, or local pressure, and no history of head radiation or disease.

An ultrasound examination of the neck lymph nodes and thyroid gland revealed multiple echogenic areas in the thyroid gland. According to the Chinese Thyroid Imaging Reporting and Data System (C-TIRADS), the microcystic acoustic image findings indicated glial retention. An enhanced computed tomography (CT) scan revealed a cystic lesion in the neck anterior cervical mass, which was initially thought to be a thyroglossal cyst. Based on both the ultrasound and examination results, the left lateral neck mass was initially diagnosed as a branchial cleft cyst. Surgery was performed to remove the neck anterior cervical mass, part of the hyoid bone, and the left lateral mass (Figure 1).

Figure 1 Ultrasound and imaging images. (A) Ultrasound of the thyroid without obvious malignant features. (B) Ultrasound of the cervical lymph nodes. Abnormal blood flow in the left anterior neck, suggestive of gill slit cysts. (C,D) Contrast-enhanced CT images of the neck. The red arrow points to the mass, and the blue arrow points to the hyoid bone in (C). (E) Contrast-enhanced CT images of the neck. The blue arrow points to the hyoid bone. CT, computed tomography.

However, an immunohistochemical (IHC) analysis of the skeletal muscle tissue of the anterior neck mass sent for examination revealed papillary thyroid carcinoma (PTC) with calcification. An ultrasound examination of the thyroid gland revealed no imaging features suggestive of PTC; nonetheless, when combined with the IHC analysis, the final diagnosis was ectopic PTC (Figure 2A-2C). After informing the patient of the histopathological results, a lymph node ultrasound examination was performed, revealing abnormal lymph nodes at levels II and III of the neck. The patient underwent a second neck dissection, and the postoperative pathology results confirmed metastases in the cervical lymph nodes (Figure 2D-2F). At the one-month postoperative follow-up, the patient was recovering well following the incision.

Figure 2 Histopathology results for the excised tissues (10× magnification). (A-C) After the lesion was excised in the first operation, H&E staining and IHC staining were performed. The IHC results were as follows: CK19(+), TPO(–), BRAF(+), and Ki67 (about 5%+). (D-F) A second operation was performed to excise the lesion. The H&E and IHC results were as follows: BRAF(+). H&E, hematoxylin and eosin; IHC, immunohistochemical.

All the procedures in this case were performed in accordance with the ethical standards of the institutional and/or national research committee(s), and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this case report and the accompanying images. A copy of the written consent form is available for review by the editorial office of this journal.

Discussion

The thyroid gland, the largest endocrine gland in the body, plays a crucial role in the growth, development, and metabolism of the body through the secretion of hormones. The thyroid gland begins to develop in the third week of gestation, originating in the pharyngeal pouch and descending to the neck, inferior to the thyroglossal bone, typically at the level of the fifth cervical vertebra to the first thoracic vertebra. Usually, the thyroid gland remains attached to the tongue through the thyroglossal duct. ETT in the gland commonly results from an embryological failure of descent. The prevalence of ETT is estimated to be between 1 in 100,000 and 1 in 300,000 individuals (2). ETT most commonly occurs at the base of the tongue (approximately 90% of cases), but it may also occur in the thyroglossal duct, and even in the mediastinum, adrenal glands, gastrointestinal tract, and other systems (1,3).

Most disease that can occur in the thyroid gland can occur in the ectopic thyroid gland, including malignant tumors. The risk of ETT becoming cancerous is extremely low; ectopic thyroid carcinoma accounts for about 0.3–0.5% of all thyroid cancer cases, and the risk factors associated with its development are not yet known (4). Cervical lymph node metastasis is common in PTC, with reported incidence rates ranging from 3.1% to 18.2% (5). Many cases of metastatic ectopic thyroid cancer have been reported, but rarely without associated lesions of the thyroid gland (5,6). ETT is generally classified into two types based on its development: aberrant thyroid gland, where the thyroid gland is absent from its normal position; and accessory thyroid gland, where the thyroid gland is in its normal position but is maldeveloped, as observed in this case (7). The clinical symptoms of ectopic thyroid carcinoma are mostly related to the site of occurrence, and the size of the tumor. When it occurs in the head and neck, it may be accompanied by hoarseness, cough, and chest pain, and when it occurs in the chest and mediastinum, it may be accompanied by dyspnea and eating disorders (4,8).

Precise epidemiological data on the incidence and frequency of ectopic thyroid carcinoma are lacking, which is clinically significant due to the difficulties in distinguishing between metastatic thyroid cancer and ectopic localized primary cancers. Distinguishing between metastatic thyroid cancer and ectopic thyroid cancer will continue to pose a significant diagnostic challenge moving forward. Thyroid cancer is usually diagnosed after the appearance of neck swelling, and the absence of clinical symptoms of ectopic thyroid cancer undoubtedly makes the clinical diagnosis more challenging (9,10). In the present case, the left-sided neck metastasis persisted for an extended period without progressive enlargement or increase, and no thyroid function or structural abnormalities were observed. Such factors may lead to misdiagnosis. This case highlights the importance of considering the possibility of ectopic thyroid cancer in the differential diagnosis of pathogenic neck tumors.

Histopathological or biopsy examination is typically used to confirm the diagnosis of ectopic thyroid cancer. Preoperative assessment through imaging and other auxiliary examinations, such as ultrasound, thyroid scintillation imaging, enhanced CT scanning, magnetic resonance imaging, puncture cytology biopsy, tissue biopsy and thyroid function tests, plays a limited role. Choosing auxiliary examination based on the condition is helpful for a clear diagnosis (11). Further research needs to be conducted to ensure the accurate diagnosis and optimal management of ETT.

Conclusions

This case shows that thyroid cancer can develop from ectopic tissue even in the absence of malignant lesion of thyroid tissue. To date, reports of ectopic thyroid carcinoma are limited. Management and treatment choices should be individualized, and include complete thyroidectomy, neck dissection, and radioactive iodine therapy. Early diagnosis and treatment may improve patient prognosis.

Acknowledgments

We thank the study participants and research staff for their contributions and commitment to this study.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://acr.amegroups.com/article/view/10.21037/acr-2025-130/rc

Peer Review File: Available at https://acr.amegroups.com/article/view/10.21037/acr-2025-130/prf

Funding: This study was supported by the National Natural Science Foundation of China (No. 82071024).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://acr.amegroups.com/article/view/10.21037/acr-2025-130/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this case were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent form is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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(English Language Editor: L. Huleatt)