A Rare Case of Thyroid Gland Metastasis from Laryngeal Cancer, Findings on [18F]FDG PET/CT

A 65-year-old male presented with swelling on the left side of his neck. The swelling was insidious in onset and progressive in nature. Upon evaluation, the patient was found to have ulceroproliferative lesion involving the supraglottis extending to the oropharynx. Punch biopsy from the lesion and fine needle aspiration cytology (FNAC) from the left neck swelling were then performed. Histopathological examination revealed moderately differentiated squamous cell carcinoma of supraglottis with metastasis to cervical lymph nodes. Subsequently, 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F FDG-PET/CT) was performed which revealed hypermetabolic heterogeneously enhancing lesion in the left vallecula, left aryepiglottic, and glossoepiglottic fold extending to the floor of mouth suggestive of primary malignancy. In addition, there were multiple hypermetabolic cervical, mediastinal lymph nodes, right 6^th rib lesion, and multiple soft-tissue lesions in bilateral lung fields as well as hypermetabolic hypodense lesion involving the right lobe of thyroid suggestive of metastatic disease [Figure 1]. FNAC from the thyroid lesion confirmed the presence of metastatic squamous cell carcinomatous deposit [Figure 2].

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Figure 1 Fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) scan performed postneoadjuvant chemoradiotherapy. Maximum intensity projection image showing hypermetabolic lesion in the neck-and-thorax region (a). Hybrid PET-CT images showing soft-tissue lesion in the right vallecula with no significant metabolic activity (white arrow) (b), Hypermetabolic multiple bilateral cervical lymph nodes (c), hypodense lesion in the right lobe of thyroid (white arrow) (d), soft-tissue lesion in bilateral lung fields (e and f) and lytic lesion involving the right 6rh rib (g) suggestive of metastatic disease

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Figure 2 Cytology images of fine-needle aspiration from the thyroid nodule at (a) ×20, (b) ×40 and (c) ×80 magnification showing atypical squamous cells in a necrotic background

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The patient then underwent local radiotherapy to the laryngeal lesion along with platinum-based chemotherapy (cisplatin+paclitaxel). Follow-up 18-F FDG-PET/CT performed 5-month postchemotherapy revealed regression in size and resolution of metabolic activity from ulceroproliferative supraglottic lesion, however, there was increase in size and metabolic activity of cervical and mediastinal lymph nodes, increase in metabolic activity of right 6^th rib lesion as well as appearance of few new lung nodules and soft-tissue deposit along right crus of diaphragm and new lesion in the isthmus of thyroid, suggesting progressive nature of the disease [Figure 3].

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Figure 3 Follow-up 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) performed post 6 cycles of adjuvant chemotherapy. (a) MIP image showing hypermetabolic lesion in the neck and thorax showing increase in size and metabolic activity with the appearance of few new hypermetabolic foci. Hybrid PET-CT images showing mildly hypermetabolic soft-tissue lesion in the right vallecula (white arrow) (b), Increase in size and metabolic activity of bilateral cervical lymph nodes (c), hypodense lesion in the right lobe of thyroid (white arrow) (d) and lytic lesion involving the right 6rh rib (g) and lung nodules (not shown). There is appearance of new lesions involving the isthmus of thyroid (white arrow) (e), and right crus of diaphragm (f) and mediastinal lymph nodes (not shown), overall suggestive of progressive disease

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Despite the significant prevalence of primary thyroid cancer, metastases to the thyroid gland are reported infrequently with an incidence of approximately 0.36%.[12] The most frequent sources of metastases to the thyroid include renal cell carcinoma, followed by lung, colorectal, and breast carcinomas with laryngeal carcinomas being rarely reported.[34] Metastasis to thyroid gland represents a rare entity and ponders a poor prognosis irrespective of the site of the primary disease with median overall survival as low as 10 months.[5] However, when suspected, it is essential to differentiate it from primary synchronous/metachronous thyroid cancer as well as from contiguous spread from adjacent metastatic disease or adjoining primary malignancy. Imaging findings, histopathology, as well as immunohistochemistry/immunocytochemistry, should be cautiously reviewed before arriving at the final diagnosis.