Ectopic thyroid follicular carcinoma in the right mandible: a case report

Introduction

Ectopic thyroid refers to the presence of thyroid tissue in locations other than the normal anterior neck region between the second and fourth tracheal cartilages (1). It is the most frequent form of thyroid dysgenesis, accounting for 48–61% of the cases (2). The prevalence of this condition is reported to be between 1 per 100,000–300,000 persons, and 1 in 4,000–8,000 patients is estimated to suffer from thyroid disease (3,4). Ninety percent of ectopic thyroids were found at the base of the tongue. Despite having a secretory function and the potential for malignancy similar to eutopic thyroid tissue, only 1% of ectopic thyroid tissues in the tongue become malignant (5). The occurrence of ectopic thyroid tissue in the mandible is infrequent, and ectopic thyroid follicular carcinoma in the mandible is exceedingly rare. The first case of MFTC underwent total thyroidectomy in situ, which indicated a nodular colloid goiter (6). Here, we present a rare and complex case involving ectopic thyroid follicular carcinoma alongside a eutopic left thyroid with isthmus follicular adenoma and a right thyroid adenomatous goiter, a specific case that has not been previously reported. To the best of our knowledge, this is the second reported instance of mandible follicular thyroid cancer (MFTC) but the first to document an MFTC with concurrent eutopic thyroid follicular adenoma and adenomatous goiter. We present this article in accordance with the CARE reporting checklist (available at https://gs.amegroups.com/article/view/10.21037/gs-24-288/rc).

Case presentation

A 72-year-old man presented with a chief complaint of pain and discomfort in the right mandibular posterior region that had persisted for over 3 months with cone-beam computed tomography (CBCT) revealing a mass in the right mandible. The patient felt pain and discomfort in his right lower posterior dental region 3 months ago. After root canal treatment on the right mandibular second molar at a clinic, no significant improvement was seen in his symptoms. A large mandibular mass was detected on CBCT, prompting the patient to seek treatment at West China Hospital of Stomatology, Sichuan University. The patient underwent a total thyroidectomy at another hospital 3 years ago. Postoperative pathology indicated that the “left thyroid and isthmus” were consistent with follicular adenoma with necrosis, while the “right thyroid” was diagnosed as an adenomatous goiter (Figure 1). Following the surgery, the patient received oral administration of levothyroxine sodium 75 µg once daily (qd).

Figure 1 Postoperative pathology slide of the patient’s eutopic thyroid lesion with hematoxylin and eosin staining.

A physical examination revealed that the right side of the patient’s face was slightly swollen compared to the left side, and the mouth opening was normal. A bony prominence approximately 3.0 cm × 3.0 cm in size was palpable in the right mandibular angle area, accompanied by severe pain. The right mandibular second molar was loose at degree II, with no abnormality in the intraoral mucosa, and numbness in the right lower lip. A CBCT scan showed the bone in the right mandibular molar area to the mandibular angle was disorganized and resorbed severely, with unclear boundaries and rough edges. A small amount of needle-like periosteal bone formation was seen on the buccal and lingual sides, and the structure of the right mandibular neural tube in the lesion area was unclear (Figure 2).

Figure 2 Cone-beam computed tomography scan showed the bone in the right mandibular molar area to the mandibular angle was disorganized and resorbed severely (A,B).

We first performed a biopsy on the patient’s right mandible to confirm the exact diagnosis. A tissue sample of size 1.0 cm × 1.0 cm × 0.3 cm was collected for examination. Postoperative pathology revealed CK5/6 (−), CK7 foci (+), CD14 (−), S-100 (−), Ki-67 (+, <3%), neuron-specific enolase (NSE) (−), chromogranin A (CGA) (−), synaptophysin (Syn) (−), P63 (focally positive), combined with morphology, epithelioid-derived tumors, and detection of suspected thyroid tissue components. Combining the imaging and biopsy findings, we considered severe destruction of the mandible due to ectopic thyroid cancer. So we opted for resection of the right mandibular tumor along with a portion of the mandible. Reconstruction was simultaneously performed using free autogenous rib grafts, decided upon after consultation with the patient and family, as they had minimal expectations for postoperative occlusal function recovery and preferred a less invasive option, and were also considering financial constraints.

The patient underwent an extended right mandibular mass resection, right hemimandibulectomy, and left seventh rib (with costal cartilage) free transplantation with titanium plate implantation and fixation in West China Hospital of Stomatology, Sichuan University (Figure 3). Intraoperatively, the lesion was found to invade the muscles outside of the mandible, causing severe destruction of the mandible. Postoperative pathology revealed a large amount of thyroid-like tissue and a low-grade adenocarcinoma (Figure 4). To further clarify the diagnosis, we sent the patient’s pathology slides to West China Hospital, Sichuan University for consultation. The immunohistochemical results were as follows: thyroglobulin (Tg) (+), TTF-1 (+), PAX-8 (+), CK19 (small foci +), galectin-3 (−), HBME-1 (−), P53 (individual +), and Ki67 positivity up to 10% focally. Genetic testing revealed a TERT gene mutation (+) at locus 228 (C>T) and an NRAS gene exon 3 mutation. No BRAF gene exon 15 point mutation (V600E) or HRAS gene codon 12/13/61 mutation was detected. Based on the histomorphology and these findings, the pathologic diagnosis was determined to be thyroid follicular carcinoma.

Figure 3 The patient underwent an extended right mandibular mass resection, and right hemimandibulectomy.

Figure 4 Postoperative pathology revealed a large amount of adenocarcinoma-like tissue with hematoxylin and eosin staining (magnification ×20).

The patient had a good postoperative recovery from clinic symptoms and functional restoration. We performed a panoramic X-ray 1 month postoperatively to check the condition of the autotransplanted rib (Figure 5). No signs of tumor progression or discomfort were observed for more than 2 months following the radical operation with simultaneous autograft bone repair.

Figure 5 A panoramic radiograph 1 month postoperatively indicated that the autotransplanted rib was well-fixed in place, with no significant absorption or destruction observed.

Ethical considerations

All procedures performed in this study were in accordance with the ethical standards of the West China Hospital of Stomatology, Sichuan University and with the Helsinki Declaration (as revised in 2013). Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Key findings

Ectopic thyroid appears primarily in the cervical midline, like lingual, sublingual, submandibular, paratracheal, and substernal locations, and even in the liver, hepatoduodenal ligament and adrenal gland, and is rarely found in the mandible (7-9). Ectopic thyroid tissue can be subject to the same pathological processes as normal eutopic thyroid tissue, such as inflammation, hyperplasia, and tumorigenesis (10,11). Ectopic thyroid carcinoma is sporadic, but it has been documented in cases of lingual thyroid, thyroglossal duct cysts, lateral aberrant thyroid tissue, and mediastinum (12,13). Instances of ectopic thyroid and ectopic thyroid carcinomas located in the mandible have also been reported in the literature (6,14).

Here, we present a rare case of follicular thyroid carcinoma in the mandible, accompanied by benign thyroid lesions in their normal anatomical positions. To our knowledge, this is the first reported case of ectopic follicular thyroid carcinoma coexisting with a follicular adenoma with necrosis in the left thyroid and isthmus, and an adenomatous goiter in the right thyroid.

Comparison with similar research

The first MFTC patient suffered a sudden death on the fourth postoperative day. Although the exact cause was not determined, this highlights the necessity of closely monitoring patients’ vital signs during such surgeries (6). Given that the patient had undergone a total thyroidectomy 3 years prior and was regularly taking levothyroxine sodium tablets postoperatively, we conducted thyroid function tests before and after the surgery (Table 1). The patient’s preoperative thyroid stimulating hormone (TSH) was significantly lower than normal, while free triiodothyronine (FT3) and free thyroxine (FT4) were higher than normal, and all returned to normal after surgery. It was considered that the ectopic thyroid tissue in the right mandible had the functional capacity of a normal thyroid gland, capable of secreting FT3 and FT4. The excessive secretion of FT3 and FT4 inhibited TSH secretion. Following surgery, the decrease in FT3 and FT4 levels led to an increase in TSH secretion. These results suggest that the patient’s ectopic thyroid tissue may have been functional. The removal of this ectopic thyroid led to a decrease in FT3 and FT4 levels, accompanied by an increase in TSH levels.

Implications and actions needed

As this malignancy is typically confirmed only after surgical excision of the lesion and subsequent pathological examination, the diagnosis is challenging. In specific cases, diagnosis can be inferred from certain features, including a separate blood supply of the ectopic gland, the absence of a personal history of malignancy, and a normal or absent eutopic thyroid with no history of surgery (12). Thyroid cancer can metastasize distantly, and many reports in the literature have proven mandibular metastases from thyroid cancer (15,16). Thus, ectopic thyroid carcinoma must be distinguished from metastasis of thyroid carcinoma. There are several differential diagnostic points that need to be noted: (I) normal thyroid-like tissue may be observed in the tissue of ectopic thyroid cancer rather than in the tissue of metastatic thyroid cancer; (II) the thyroid gland in situ in metastatic thyroid cancer exhibits malignant tumors, whereas in patients with ectopic thyroid cancer, the thyroid gland in situ is mostly normal; (III) in cases of metastatic thyroid cancer, lymphoid tissue can be easily found. Furthermore, it is worth mentioning that we consulted the patient’s original pathologist and reconfirmed the diagnosis of the in situ thyroid lesion, which aligns with the initial diagnosis.

This case underscores the importance of considering diverse differential diagnoses when encountering atypical mandible lesions, possibilities such as vascular-origin tumors, distant metastases from malignant tumors, or, as in this patient, carcinoma of an ectopic thyroid gland should be contemplated. An initial biopsy can be selected, and further comprehensive considerations must be given to determine the best treatment plan. Additionally, in 70–90% of cases of ectopic thyroid gland, it is the only thyroid tissue present (17). Therefore, for patients with ectopic thyroid gland, ectopic thyroid carcinoma, or metastatic thyroid malignancies, it is crucial to monitor their thyroid function perioperatively and postoperatively to mitigate the risks associated with thyroid function abnormalities.

Conclusions

In conclusion, we present a rare case of ectopic follicular thyroid carcinoma located in the right mandible, accompanied by a benign eutopic thyroid tumor. This condition should be considered in the differential diagnosis of mandibular lesions. Effective management of such cases necessitates a multidisciplinary approach.

Acknowledgments

Funding: This work was supported by the Sichuan University Postdoctoral Interdisciplinary Innovation Fund (No. JCXK2228 to Y.C.), and the Natural Science Foundation of Sichuan Province (No. 2022NSFSC0635 to X.T., No. 2023NSFSC0704 to B.H.).

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://gs.amegroups.com/article/view/10.21037/gs-24-288/rc

Peer Review File: Available at https://gs.amegroups.com/article/view/10.21037/gs-24-288/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://gs.amegroups.com/article/view/10.21037/gs-24-288/coif). Y.C. received supports from the Sichuan University Postdoctoral Interdisciplinary Innovation Fund (No. JCXK2228). X.T. received supports from the Natural Science Foundation of Sichuan Province (No. 2022NSFSC0635). B.H. received supports from the Natural Science Foundation of Sichuan Province (No. 2023NSFSC0704). The other 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 study were in accordance with the ethical standards of the West China Hospital of Stomatology, Sichuan University and with the Helsinki Declaration (as revised in 2013). Written informed consent was obtained from the patient for the publication of this case report and accompanying images. A copy of the written consent 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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