CYTOLOGICAL DIAGNOSIS OF EXTRA THYROIDAL MALIGNANCY IN THYROID-A REPORT OF TWO CASES

Dr. K. Kokila 1 . Dr. Vijaya baskar 2 , Dr. Geetha Devadas 3 and Dr. Bharathi Vidhya Jayanthi 4 . 1. Post graduate in pathology, Madras Medical College. 2. Assistant professor of pathology, Madras Medical College. 3. Professor of pathology, Madras Medical College. 4. Director & Professor of pathology, Madras Medical College. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Intra thyroidal metastasis and direct extension of extra thyroidal malignancies can present with clinically palpable nodules and as suspicious nodules on radiological imaging. Metastasis to thyroid is rare and usually discovered during an autopsy especially in individuals with widespread dissemination of the tumor. In autopsy series, the incidence of thyroid metastasis ranges from 0.5% to 24% (1) but is much lower in clinical studies. Most common primary tumors that can metastasize to thyroid include carcinoma of kidney, breast, pancreas, colon, ovary, lung, bladder and malignant melanoma (2) . It is rare for these tumors to present initially as isolated thyroid nodule or disturbances in thyroid function and is seen in less than a quarter of cases (3) . We reported two cases of extra thyroidal malignancies which were diagnosed by fine needle aspiration cytology. The first case was an invasive breast carcinoma that metastasized to thyroid and another case was direct extension of squamous cell carcinoma of hypopharynx to thyroid. Primary squamous cell carcinoma of the thyroid is rare and its incidence ranges from 0.2-1.1% of all thyroid malignancies (4) . Whenever malignant squamous cells are seen admixed with thyroid follicular epithelial cells, the possibility of metastasis from occult primary should always be considered while interpreting thyroid cytology. Squamous cell carcinomas metastasizing to the thyroid largely have their origin in the esophagus, lung and head & neck region. Invasive breast carcinoma is the most common type of breast cancer which constitutes 85% of all invasive carcinomas. Breast carcinoma usually metastasizes to lungs, liver, bones and brain. Solitary thyroid metastasis of invasive breast carcinoma is rare.

Case-1:-
A 60 year old female patient presented with swelling in front of neck for 3 months and swelling in right breast for 6 months. Patient had sudden increase in the size of thyroid swelling. On examination, there was asymmetrical enlargement of the thyroid and was firm in consistency. A swelling of size 4x3cm was noted in the upper outer quadrant of right breast. Fine needle aspiration was done in both the swellings and hemorrhagic aspirate was obtained. The breast swelling was reported as ductal carcinoma and thyroid swelling was reported as metastatic carcinomatous deposits from breast. Core needle biopsy was performed in the breast and reported as invasive breast carcinoma.

Case-2:-
A 40 year old female patient presented with dysphagia for 6 months with history of voice change. On examination, there was asymmetrical enlargement of the thyroid which was firm in consistency. Imaging showed a hypopharyngeal growth with lateral extension to adjacent structures. Fine needle aspiration was done from the thyroid swelling and hemorrhagic aspirate was obtained. Microscopy revealed features of squamous cell carcinoma extending into thyroid. Later biopsy was performed from the hypopharyngeal growth and reported as infiltrating squamous cell carcinoma with moderate differentiation. 1615

Discussion:-
The exact incidence of secondary tumors of the thyroid is not clear, because it is not often examined or routinely investigated by imaging, during a metastatic workup. Malignancies metastasizing to the thyroid portend a dismal prognosis.
Secondary thyroid tumors account for 0.1% of all thyroid nodular lesions investigated by fine needle aspiration cytology (5) .
Secondary thyroid cancers may occur as a result of direct extension from nearby structures or metastasis via the blood stream from distant sites. Direct invasion from esophagus and head & neck tumors are far more common than hematogenous spread. The plausible reasons for rare hematogenous spread are abundant blood flow which hinders the seeding of tumor cells, hyperoxic environment and high iodine content which inhibit the development of metastatic tumor cells (6) .
The mean time interval between initial cancer diagnosis and metastasis to thyroid is 8.8 years for kidney, 10.9 years for breast and 11 years for uterus.
Metastasis to the thyroid is more commonly an autopsy diagnosis but in some cases it could be detected clinically.
The patient might present with diffuse swelling of the thyroid or a nodule, dysphagia, dyspnea, dysphonia and cough (8) .
Metastatic tumors to the thyroid can easily mimic as primary thyroid cancers. Thus, it has to be differentiated from primary thyroid tumors. A detailed clinical history, radiological imaging and histopathological correlation are necessary in arriving at an accurate diagnosis. The diagnosis provided by fine needle aspiration cytology is similar to that of histopathology in diagnosing secondary tumors of the thyroid.
Some cytologic pointers indicating towards secondary malignancy are the presence of keratin, mucin, melanin and bile admixed with benign appearing thyroid follicular epithelial cells and malignant cells that are not relative to the parent organ. Ancillary techniques have to be performed in equivocal cases and this helps in identifying the metastatic lesions.

Conclusion:-
Secondary tumors of the thyroid are uncommon, but can create a diagnostic dilemma to the pathologist. Thus, in any patient with a previous history of malignancy, no matter how remote that history is, a new thyroid lesion should be considered as a metastatic deposit until proved otherwise.