|Year : 2019 | Volume
| Issue : 2 | Page : 84-87
A rare case of follicular adenoma in an ectopic mediastinal thyroid
Salwa Bano, Veena Ramaswamy, BN Tejaswini, Chaitra Chandrashekar
Department of Histopathology, HCG Cancer Centre, Bengaluru, Karnataka, India
|Date of Web Publication||15-Jul-2019|
Dr. Salwa Bano
No. 120, F2, Emaar Paradise, 4th Main, 2nd Cross, BTM 1st Stage, Bengaluru - 560 029, Karnataka
Source of Support: None, Conflict of Interest: None
Ectopic thyroid refers to the presence of thyroid tissue located far from its usual anatomic place with no vascular connection to the main gland. Ectopic thyroid tumor is a thyroid neoplasm that occurs in sites other than the cervical thyroid gland. Ectopic thyroid tumors arising in the mediastinum without connection to the cervical thyroid gland are very rare. They are either discovered incidentally or present with symptoms referable to a mediastinal mass. We present a case of a mediastinal ectopic thyroid in a 70-year-old man investigated for chest pain and cough. Radiology showed a well-defined lesion in the mediastinum. Biopsy and resection specimens showed follicular adenoma of the thyroid. On immunohistochemistry, tumor was reactive for thyroglobulin. The possibility of ectopic thyroid in the mediastinum which can be a site for adenoma or carcinoma of the thyroid should be considered in the differentials of a mass lesion in the mediastinum. Symptomatic diseases should be treated surgically.
Keywords: Ectopic thyroid, follicular adenoma thyroid, mediastinal thyroid tissue
|How to cite this article:|
Bano S, Ramaswamy V, Tejaswini B N, Chandrashekar C. A rare case of follicular adenoma in an ectopic mediastinal thyroid. Thyroid Res Pract 2019;16:84-7
|How to cite this URL:|
Bano S, Ramaswamy V, Tejaswini B N, Chandrashekar C. A rare case of follicular adenoma in an ectopic mediastinal thyroid. Thyroid Res Pract [serial online] 2019 [cited 2019 Dec 10];16:84-7. Available from: http://www.thetrp.net/text.asp?2019/16/2/84/262732
| Introduction|| |
The discovery of ectopic thyroid tissue is rare, with an incidence of about one case in 300,000. Localization in the mediastinum is very rare. Thyroid tissue migrates from the foramen cecum along the thyroglossal duct to reach its final anterotracheal position. Ectopic thyroid tissue can be located all along this migration route, the most common site of localization being tongue. The molecular mechanisms implicated in this process are not fully elucidated. Mutations of genes regulating thyroid gland development have been postulated. We report a case of ectopic thyroid tissue in a 70-year-old man undergoing explorations for chest pain and cough.
| Case Report|| |
A 70-year-old man from Tanzania presented with symptoms of chest pain and persistent dry cough for 7 months. The patient had no significant history. The physical examination found no overt signs of respiratory failure or heart failure. Blood tests showed normal cell counts, no signs of inflammation, and normal lactate dehydrogenase levels. Tumor markers such as carcinoembryonic antigen, alpha-fetoprotein, human chorionic gonadotropin, and prostate-specific antigen were done which were within normal limits. The patient was euthyroid.
Neck ultrasound showed a normally positioned thyroid gland with no nodules and no lymph node enlargement. Positron emission tomography–computed tomography scan [Figure 1] revealed a 9.6 cm × 6.8 cm × 9.1 cm heterogeneous, well-defined right paratracheal soft-tissue mass showing few internal foci of calcifications and nonenhancing areas of necrosis.
|Figure 1: Axial section of thorax showing a large heterogeneously enhancing lesion (asterisk) in the right paratracheal region measuring 9.8 cm × 6.3 cm with patchy calcifications originating from nerve root T5. Lesion is in the middle and posterior mediastinum. The thecal sac and lung parenchyma appear unremarkable|
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Pathological examination of the biopsy [Figure 2] specimen showed thyroid tissue with variably sized follicles, filled with colloid, and lined by bland follicular cells. Immunohistochemistry (IHC) was performed which showed immunoreactivity for CK-7 and thyroglobulin indicating a thyroid origin of tumor. IHC challenges for CK-20 and CK-19 were negative [Figure 3]. Thus, a differential of ectopic thyroid tissue versus a follicular neoplasm of the thyroid was offered.
|Figure 2: (a) Biopsy of the lesion showing a neoplasm with evidence of thyroid follicular cell differentiation with cells arranged in microfollicular and macrofollicular patterns (H and E, ×10). (b) Cells are bland and without nuclear features of papillary thyroid carcinoma, (H and E, ×40)|
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|Figure 3: Immunohistochemistry staining performed on the biopsy section. Thyroid follicles show diffuse and strong membranous reactivity to thyroglobulin (a) and CK-7 (b) and immunonegativity to antibody CK-20 (c) and CK-19 (d). These immunohistochemistry features are consistent with a benign thyroid primary lesion|
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Complete resection of the mediastinal mass was performed eventually and sent for frozen section assessment. The surgeon did not note a channel linking the ectopic tissue with the thyroid gland preoperatively. Grossly, the specimen measured 9.5 cm × 9 cm × 7 cm and weighed around 450 g [Figure 4]. The lesion was entirely capsulated, and cut surface showed a homogenous, soft-to-firm, tan, brown lesion. Areas of calcification were noted. Many dilated vessels filled with blood were seen. On frozen section, a probable diagnosis of follicular neoplasm was extended. Consequently, on histopathological examination [Figure 5], a cellular lesion composed of closely packed follicles was seen. The lesion was completely enveloped by thin fibrous capsule. Cells lining the follicles were cuboidal to low columnar and appeared pale staining with inconspicuous nucleoli. Secondary changes of hemorrhage, hemosiderin deposition, sclerosis, zones of interstitial fibrosis, edema, and cystic changes were noted. Calcification was also seen, but psammoma bodies were not identified. Papillary hyperplasia was noted in some of the dilated follicles. No evidence of capsular or vascular invasion was seen even after thorough sampling. No mitotic figures were noted. No papillary nuclear features were evident. No areas of necrosis were seen. There was no sign of malignancy. Thus, a diagnosis of “follicular adenoma arising in an ectopic thyroid gland in the mediastinum” was articulated. IHC was not repeated on the excised specimen.
|Figure 4: Gross picture of mediastinal mass showing the solid and tan-brown cut surface of the lesion with areas of hemorrhage (chevron) and calcification (notched arrow). Many dilated vessels are evident macroscopically (thin arrows)|
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|Figure 5: (a) Sections from the resected mass show similar morphology as that of the biopsy. No evidence of capsular or vascular invasion seen (H and E, ×40). (b) Areas showing thyroid follicles with secondary changes, namely hemosiderin deposition (arrowhead) and cholesterol clefts (arrow, H and E)|
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| Discussion|| |
Ectopic thyroid refers to the presence of thyroid tissue located far from its usual anatomic place with no vascular connection to the main gland. Ectopic thyroid tissue occurs in about 7 to 10% of the general population. More than 99% of thyroid cancers arise eutopically within the thyroid gland. Ectopic thyroid tumors are extremely rare. They are either discovered incidentally, or present with symptoms referable to a mediastinal mass. Our case presented with chest pain and recurrent dry cough.
Ectopic thyroid tissue results from developmental defects during early stages of thyroid gland embryogenesis, during its migration from the foramen cecum to its final pretracheal position. It can be found along the course of the thyroglossal duct or laterally in the neck as well as in distant places such as the mediastinum. Ectopic thyroid tissue can be subject to the same pathological processes as normal ectopic thyroid tissue such as inflammation, hyperplasia, and tumorigenesis.
Differential diagnosis for mediastinal thyroid includes germ cell tumors, neurogenic tumors, lymphomas, and thymic and mesenchymal tumors. Follicular adenoma and papillary carcinoma are the most common types of tumors described in an ectopic thyroid tissue. In our case, histopathology was characteristic of a follicular adenoma. Moreover, no IHC help was required for the diagnosis in our case on the excised specimen. However, IHC for thyroglobulin was performed on the biopsy as the World Health Organization recommends immunostaining to confirm thyroid origin.
One of the unusual features of this case is the combination of ectopic thyroid tissue in the mediastinum and a normally functioning thyroid gland in the neck. This situation is rarely described in the literature. The majority of patients with thyroid ectopy are asymptomatic, but obstructive symptoms and hypothyroidism have been observed. Hyperthyroidism is an exceptionally rare finding. Our case was euthyroid.
Information on the behavior of these tumors is limited, but it is likely that the outcome is similar to comparable stage tumors occurring in the cervical thyroid gland.
The gold standard treatment for ectopic thyroid tissue in the mediastinum is surgical resection, especially in the presence of signs of local compression. Surgery is followed by radioiodine ablation and levothyroxine suppressive therapy in refractory cases.
| Conclusion|| |
Our case suggests that ectopic thyroid tissue should be entertained as a tentative diagnosis in patients presenting with mediastinal mass, even in those with a normally located and normally functioning thyroid gland, since the neoplastic potential of these lesions requires surgical interference.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]