| Abstract|| |
Benign ectopic thyroid tissue within the parotid gland is very rare with only one case reported till date in the world literature. We report a case of ectopic thyroid in the left parotid gland with an orthotopic thyroid in an elderly female, who was presented to us with the simultaneous onset of right-sided thyroid swelling and left parotid swelling for 6 months. Fine-needle aspiration cytology (FNAC) was done from both the swellings and a diagnosis of Hurthle cell neoplasm metastasizing to the left parotid gland was initially made. However, histopathological examination along with the immunohistochemistry (IHC) panel proved it to be an ectopic thyroid in the parotid. The case is being documented here for its rarity as well as an unusual presentation so that the readers are aware of this entity and the complete workup required to prevent diagnostic pitfalls.
Keywords: Ectopic thyroid in salivary glands, follicular acinic cell tumors, Hurthle cell neoplasms, lateral thyroids, metastatic thyroid
|How to cite this article:|
Singh A, Yadav K, Kumar M, Misra V. Ectopic thyroid in left parotid gland with an orthotopic thyroid gland: A rare case scenario. Indian J Pathol Microbiol 2021;64:780-2
|How to cite this URL:|
Singh A, Yadav K, Kumar M, Misra V. Ectopic thyroid in left parotid gland with an orthotopic thyroid gland: A rare case scenario. Indian J Pathol Microbiol [serial online] 2021 [cited 2022 Sep 28];64:780-2. Available from: https://www.ijpmonline.org/text.asp?2021/64/4/780/328576
| Introduction|| |
Ectopic thyroid tissue is a rare developmental abnormality involving aberrant embryogenesis of the thyroid gland during its passage from the floor of the primitive foregut to pretracheal position. An ectopic thyroid coexisting with an orthotopic thyroid is even rarer, but not so if there is some coexisting thyroid disease. Few rare case reports also mention dual and triple ectopic thyroids.,
The ectopic thyroid most commonly encountered is the lingual thyroid. Extralingual thyroid tissue has been described in various parts of the head and neck region, mediastinal organs, gastrointestinal organs, and reproductive organs.
All diseases that can affect normal thyroid can also involve the ectopic thyroid. It is fundamental to exclude a metastasis from well-differentiated thyroid cancer, even when primary thyroid carcinoma is not demonstrable before labeling any thyroid tissue as an ectopic.
We report here a case of ectopic thyroid in the parotid gland in an elderly female with an orthotopic thyroid gland, which we initially misdiagnosed as a metastatic thyroid tumor in parotid on cytology. We could find only one case of ectopic thyroid in parotid even after an extensive search of literature making this one the second case.
| Case Report|| |
A 65-year-old female presented to the Department of Otorhinolaryngology with complaints of progressively and simultaneously growing right-sided thyroid swelling and left parotid swelling for 6 months. Her general condition otherwise was unremarkable. The thyroid swelling was 3 × 3 cm, diffuse, firm, nontender, and moved with deglutition. The parotid swelling was 2 × 2 cm, firm, mobile, and nontender. The ultrasonography neck done suggested multinodular goiter of thyroid and the parotid swelling as neoplastic. Fine-needle aspiration cytology (FNAC) was done from both the swellings, smears prepared from which showed similar morphology comprising of follicular epithelial cells in clusters with frequent Hurthle cell changes and lymphocytic impingement suggestive of autoimmune thyroiditis. In addition, in the thyroid aspirate, focal Hurthle cell areas showed features such as monomorphism, increased N: C ratio, nuclear overlapping, fine nuclear chromatin with prominent nucleoli, and negligible colloid suggesting a neoplastic change [Figure 1]a and [Figure 2]a. Hence, a diagnosis of Hurthle cell neoplasm in the background of autoimmune thyroiditis with metastasis to the left parotid was thought of. A histopathological examination was advised for confirmation. Also, an ultrasound of the abdominopelvic area was asked to rule out metastasis from struma ovarii. The ultrasound report was unremarkable. Her thyroid function tests were within normal limits.
|Figure 1: (a) Smear from thyroid aspirate showing Hurthle cells with moderate anisonucleosis, nuclear enlargement, and overlapping; occasional lymphocytic impingement seen (PAP 40×). (b) Cut surface of the well-encapsulated right hemithyroidectomy showing two nodular areas, smaller one is homogenous yellow and the larger one is gray-white to gray-yellow with hemorrhagic and necrotic area in the center. (c) Section showing three distinct areas. Hurthle cell adenoma in the center (asterisk) surrounded by a thick rim of hyperplastic colloid goiter (arrowhead) and thick fibrous capsule (arrow) (H and E, 4×). (d) Section showing Hurthle cell adenoma with back-to-back thyroid follicles lined by oncocytic epithelium and moderate nuclear atypia (H and E 40×). (e) Hurthle cell adenoma showing negativity for HBME-1 (IHC 40×)|
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|Figure 2: (a) Smear from parotid aspirate showing benign-looking Hurthle cells (PAP 40×). (b) Section from the parotid biopsy showing extensive areas of hyperplastic colloid goiter in the deep lobe; inset shows the normal salivary gland tissue seen in the superficial lobe (H and E 10×). (c) Section from the parotid biopsy showing strong nuclear positivity for thyroid transcription factor-1 (TTF-1) (IHC 40×). (d) Another section from the parotid biopsy showing strong cytoplasmic positivity for thyroglobulin (IHC 4×)|
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We received a completely encapsulated right hemithyroidectomy measuring 9 × 5 × 4 cm in size [Figure 1]b and a partially encapsulated left parotidectomy specimen in multiple pieces. Histopathology of the thyroid showed predominantly areas consistent with a hyperplastic colloid goiter. However, few foci showed apposed back-to-back follicles (solid pattern) lined by atypical looking Hurthle cells with regular round nuclei and no colloid [Figure 1]c. No nuclear features of papillary neoplasm were seen, neither any foci of capsular or vascular invasion were seen anywhere. These areas were consistent with a Hurthle cell neoplasm [?Adenoma ?? Undetermined Malignant Potential] [Figure 1]d.
Sections examined from the superficial lobe of the parotid gland showed normal salivary gland histology, whereas sections from the deeper lobe showed extensive areas of hyperplastic colloid goiter. No neoplastic foci were seen anywhere [Figure 2]b.
Since the neoplastic areas seen in the thyroid were totally encapsulated and no such neoplastic foci were seen in the parotid, a possibility of ectopic thyroid in the parotid was considered. Immunohistochemistry (IHC) for CD56 and HBME-1 in the thyroid tissue was done. CD56 was positive and HBME-1 was negative ruling out the possibilities of Hurthle cell tumor of uncertain malignant potential and a papillary origin of the tumor respectively, thereby confirming it to be a Hurthle cell adenoma. [Figure 1e]. Thyroglobulin and thyroid transcription factor-1 (TTF-1) were done in the parotid tissue to prove the thyroidal origin of the follicles, both of which were positive confirming it to be an ectopic thyroid in parotid [Figure 2]c and [Figure 2]d.
The patient was not given any adjuvant therapy after surgery and was doing well till the last follow-up done, which was 6 months after diagnosis.
| Discussion|| |
Ectopic thyroid is defined as a thyroid tissue that is not located anterolaterally to the second, third, and fourth tracheal cartilages. Though commonly found anywhere between the foramen cecum and the normal position of the thyroid gland, it has also been described in various parts of the head and neck, mediastinum, and abdominopelvic region. Only one case till date has been reported in the parotid gland. Very rarely cases of dual and triple ectopy have also been reported.,,
Mutation of thyroid transcription factor 2, which is required for the downward migration of the thyroid gland, has been proposed as a possible mechanism. However, ectopic thyroid tissue in the parotid area is difficult to explain by abnormal migration as it is distant from the path of embryological development. The possibilities could be a heteroplasia or metaplasia. Before labeling a thyroid tissue in parotid as ectopic it is imperative to rule out the presence of a metastasis from a thyroid carcinoma or a malignant struma ovarii, which in itself is very rare to occur.
The prevalence of ectopic thyroid is about 1 per 100,000–300,000 people, rising to 1 per 4000–8000 patients with thyroid disease. It is most common in females, especially of Asian origin. It may occur at any age but is most common at a younger age. An ectopic thyroid can show all the benign and neoplastic changes that are seen in a normally located thyroid gland. The rate of malignant transformation in ectopic thyroid is no greater than in a normally placed thyroid. Most tumors reported are papillary carcinomas, rest all types being very rarely described.
In the present case, few foci in the thyroid smears showed areas suggestive of a Hurthle cell neoplasm. Though these neoplastic areas were not seen in the parotid aspirate smears, still the possibility of a metastatic Hurthle cell neoplasm could not be completely ruled out. However, on histopatholgy, the neoplastic area in the thyroid was found to be well encapsulated, the benign nature of which was further confirmed by CD56 positivity and HBME-1 negativity on IHC. The parotid gland did not show any such neoplastic areas and the thyroidal origin of the hyperplastic follicles seen was confirmed by positive staining for thyroglobulin and TTF 1. In the only one case reported of ectopic thyroid in parotid till date, the ectopic thyroid tissue showed features of colloid goiter with cystic degeneration. The only primary parotid gland tumor that may bear a resemblance to thyroid tissue is the acinic cell carcinoma with a follicular pattern. However, it will show acinar cells with cytoplasmic basophilic zymogen granules and staining for thyroglobulin will be negative.
There is no consensus about the optimal therapeutic strategy, perhaps due to the rarity of this clinical entity. Most authors recommend complete surgical resection, considering the potential of malignant transformation. For cases completely asymptomatic/mildly symptomatic, only regular follow-up may be required.
This case is presented here to make pathologists aware of this rare entity while encountering similar lesions in parotid so that an erroneous misdiagnosis of these as metastatic thyroid tumors may be avoided after an extensive workup, which if not done may lead to unnecessary aggressive treatment of the patient that may be totally uncalled for.
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Conflicts of interest
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Department of Pathology, M.L.N. Medical College, Lowther Road, George Town, Prayagraj - 211 002, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]