Radiological Case: Squamous Cell Carcinoma of the Thyroid With Lymph Nodal and Pulmonary Metastases

Ankita Chauhan, MBBS, MD; Radha Sarawagi, MD; Aman Kumar, MD, EBIR; Rajesh Malik, MD

Disclosures

Appl Radiol. 2018;47(12):22-27. 

In This Article

Discussion

Thyroid cancer is the most common endocrine malignancy and is the seventh-most common cancer in women. Typically, these malignancies arise from the normal thyroid tissues and are of papillary, follicular, or medullary histology.[1] Primary squamous cell carcinoma (SCC) of the thyroid is a sporadic malignant disease because the thyroid lacks squamous cells. The disease is almost always fatal. Fewer than 100 cases have been reported in the literature;[2] it represents <1% of all primary carcinomas of the thyroid gland.[3,4] Overall survival usually does not exceed 6 months' post-diagnosis. In our case, there was progressive tracheal compression on short-term follow-up.

Primary SCC usually affects older patients between the 5th and 6th decades and is traditionally associated with a history of goiter. In most cases, the patient presents with a rapidly enlarging neck mass with local infiltration, followed by symptoms of compression of adjacent neck structures, such as dyspnea and hoarseness.[3] Metastases from primary SCC are common, especially to cervical lymph nodes (35%), but they may also occur in the lungs, bones, liver, kidney, and heart.[4]

Although CT is the preferred imaging modality, both CT and magnetic resonance imaging (MRI) scans are useful for assessing and characterizing thyroid swellings. They allow delineation and differentiation of thyroid masses from adjoining neck masses and enable assessment of the adjacent laryngotracheal region to discern displacement, luminal narrowing, and vascular displacement and invasion. Evaluation should also assess calcification, cyst formation, necrosis, hemorrhage, lesion margin definition and extraglandular extension. Computed tomography of the chest, abdomen, and pelvis helps exclude a primary source for secondary SCC of the thyroid gland.[5]

SCC is of unknown etiology, as the thyroid typically lacks squamous epithelium. There are three theories to explain the pathophysiology. First, the embryonic nest theory postulates the origin of squamous cells from the remnants of thyroglossal duct or the epithelium of the thymus.[4,6] Second, the metaplasia theory suggests that these cells present because of environmental stimuli (inflammation and Hashimoto's thyroiditis).[7] Third, the de-differentiation theory indicates that existing papillary, follicular, medullary, and anaplastic thyroid carcinoma de-differentiate into SCC.[8]

Cho et al performed a systematic review and individual participant data meta-analysis regarding primary SCC of the thyroid. In this meta-analysis of 89 patients, SCC presents at a mean age of 63 years (range 24–90 years) with a two-times female preponderance and anterior neck mass as the most frequent presenting complaint. Fine-needle aspiration cytology (FNAC) could accurately diagnose the cases in less than one-third of patients (as in our case) with more than half remaining nondiagnostic or giving papillary thyroid carcinoma as a false diagnosis. Complete surgical resection of the tumor was the only significant prognostic factor in the multivariate analysis, but the benefit of adjuvant treatment could not be proven. Moreover, the prognosis of these patients was poor (only 20% 3-year survival rate).[9]

Anaplastic thyroid carcinoma, carcinoma showing thymus-like elements (CASTLE) disease of the thyroid gland and metastasis from adjacent organs are the differentials to be kept in mind while diagnosing squamous cell carcinoma of the thyroid.[3]

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