The thyroid gland is not an usual site for metastasis despite, being second to the adrenal gland in terms of relative vascular perfusion. The most common cause of metastasis to the thyroid gland is the renal cell carcinoma. [1] The thyroid gland is not the most common site of metastasis in case of an esophageal malignancy.

A 60-year-old Indian female was presented with complaints of swelling in the neck for last one month which increased in size rapidly during this period. Two weeks later, she developed dysphagia for solids. Her voice was normal and she had no difficulty in breathing. There were no clinical features of hypothyroidism or hyperthyroidism. On examination, left lobe of the thyroid gland was enlarged measuring 6x4 cm, hard in consistency and having restricted mobility. Carotid pulsations were felt on both the sides. Hard single, Level II and III, cervical lymph nodes were palpable on the left side. (Figure 1) She was found to be in hypothyroid state on biochemical tests hence started on 100 mg of thyroxine daily.

Ultrasound scan of the thyroid gland revealed heterogeneous thyroid gland with enlarged isthmus and left lobe with a heterogeneous nodule in the left lobe of the gland. Enlarged lymph nodes were present at IB, II, III and IV levels. Fine needle aspiration cytology (FNAC) from the thyroid gland and cervical lymph nodes showed the presence of poorly differentiated squamous cell carcinoma with possibility of metastatic deposits in view of associated features of thyroiditis. (Figure 2) (Figure 3) Possible primary sites were considered and in view of history of dysphagia. Barium swallow and upper gastrointestinal endoscopy was done. Barium studies revealed asymmetric, concentric luminal narrowing in mid-esophagus level at the level of carina with mucosal irregularity and apple core appearance. (Figure 4A–B) Upper gastrointestinal endoscopy revealed the presence of ulcerative growth involving the full circumference of the mucosa 20 cm from the incisors and biopsy from this site showed infiltrating squamous cell carcinoma. (Figure 5) It was decided to treat the patient with chemoradiation.

Squamous cell carcinoma of the thyroid is an extremely rare entity with an incidence of 1.4–2.5% of the thyroid malignancies. [2] Normally, in a thyroid gland squamous epithelium is not present but as a result of long standing inflammation intra thyroid squamous cells may be associated with embryonic remnants or result from metaplastic transformation of native follicular epithelia. [3] The exact etiology for primary thyroid malignancy is not known. However, the proposed theory includes metaplasia theory (squamous metaplasia of the underlying thyroid disease) and embryonic rest theory (squamous cells originating from the remnant of the ultimobranchial duct or the thyroglossal duct).

Metastatic squamous cell carcinoma of the thyroid is more common. The most common sites of metastasis to the thyroid gland originate from the lungs, breast and kidneys. [4] Most of the series report carcinoma of kidney, colon and melanoma as the frequent primaries from which metastatize to thyroid. [5] Thyroid gland is an unusual site of metastasis from esophageal carcinoma. The etiopathogenesis of secondary metastatic squamous cell carcinoma (SCC) of the thyroid can be divided into three groups:

1. Direct extension from adjacent primaries like esophageal or laryngeal carcinoma.
2. Hematogenous spread from the lungs or other primary sites.
3. Retrograde lymphatic spread is rare. [6]

Secondary lesions that occur in the thyroid gland are usually solitary. [7] In certain cases, it can also present as a solitary thyroid nodule instead of a diffuse enlargement of the thyroid gland. [6] In our case too, it was solitary enlargement of the left lobe of thyroid. The usual presentation is the rapid enlargement of a neck mass (hard in consistency) with or without cervical lymphadenopathy. It may be associated with other symptoms such as dyspnea, dysphagia and hoarseness of voice. This usually occurs due to secondary infiltration to the adjacent structures. Our patient also presented with dysphagia and a rapidly developing midline neck mass with the presence of cervical lymphadenopathy. Metastatic carcinoma to the thyroid gland from the esophagus is a very rare occurrence. [6] Large autopsy series very rarely demonstrated esophageal metastasis to the thyroid (<1%). [8] In these patients thyroid function tests are usually within normal limits and hypothyroidism or hyperthyroidism are infrequent findings. [9] Our patient was diagnosed with hypothyroidism and was started on thyroxine 100 mg once daily on empty stomach. Thyroid function tests returned to normal limits within one month of initiation of the therapy and the patient was advised to continue with the same treatment.

The FNAC is usually an important tool for the diagnosis as it helps to know the nature of neoplasm with accuracy in most of the cases. [10] In our case, FNAC from the thyroid gland and cervical lymph nodes showed the presence of poorly differentiated squamous cell carcinoma with possibility of metastatic deposits. However, the limitation of FNAC is that differentiation between anaplastic thyroid carcinoma and metastatic lesions are difficult. [4] SCC of the thyroid immunohistochemically stains for cytokeratin but not for Thyroid Transcription Factor I and thyroglobulin, which are considered to be markers for follicular and papillary carcinoma. The differential diagnosis may also include tumors showing thymic or branchial pouch differentiation as it occurs in the neck in close proximity to the thyroid gland and has a squamous or mucinous differentiation. [10] These have recently been named spindle epithelial tumor with thymus like differentiation (SETTLE) or carcinoma showing thymus like differentiation (CASTLE). [7] The most unusual feature about the case was that it presented as a thyroid nodule with malignant cervical lymphadenopathy, but finally led to the diagnosis of secondary deposits from esophageal malignancy rather than a primary thyroid malignancy.

All uncommon thyroid malignancies and atypical neck masses must be thoroughly investigated as all neck masses are not related to primary thyroid conditions. This is important to avoid unnecessary thyroidectomies in patients having already widespread metastasis and poor prognosis.

1. Chen H, Nicol TL, Udelsman R. Clinically significant, isolated metastatic disease to the thyroid gland. World J Surg 1999 Feb;23(2):177–80.   [CrossRef]   [Pubmed]    
2. Menegaux F, Chigot JP. Thyroid metastases. Ann Chir 2001 Dec;126(10):981–4. [Article in French].   [Pubmed]    
3. Sahoo M, Bal CS, Bhatnagar D. Primary squamous-cell carcinoma of the thyroid gland: New evidence in support of follicular epithelial cell origin. Diagn Cytopathol 2002 Oct;27(4):227–31.   [CrossRef]   [Pubmed]    
4. Nakhjavani NK, Gharib H, Goellner JR, van Heerden JA. Metastasis to the thyroid gland. A report of 43 cases. Cancer 1997 Feb 1;79(3):574–8.   [CrossRef]   [Pubmed]    
5. Ivy HK. Cancer metastatic to thyroid: A diagnostic problem. Mayo Clin Proc 1984 Dec;59(12):856–9.   [CrossRef]   [Pubmed]    
6. Moulick A, Guha P, Das A, Das AK. Squamous Cell Carcinoma of Proximal Esophagus with Simultaneous Metastasis to Thyroid & Sternum: A Case Report with Review of the Literature. Tannaffos 2012;11(1):67–70.    
7. Basu S, Nair N, Borges AM. Squamous cell carcinoma of esophagus masquerading as solitary thyroid nodule. Indian Journal Of Cancer 2005 Oct-Dec;42(4):205–7.   [Pubmed]    
8. Meissner W, Warren S 1971.Distribution of metastases in 4012 cancer autopsies. In: Anderson WAD (ed) Pathology. Vol 1,6 ed. Mosby, St. Louis, MO, pp 538    
9. Bandyopadhay SK, Bandyopadhay R, Dutta A. Isolated massive thyroid metastasis in lung cancer. Singapore Med J 2006 Apr;47(4):324–6.   [Pubmed]    
10. Bae WK, Shim HJ, Choi YD, et al. Severe hypothyroidism induced by thyroid metastasis of cholangiocarcinoma. Cancer Res Treat 2009 Mar;41(1):56–8.   [CrossRef]   [Pubmed]