Follicular Thyroid Carcinoma Presenting as a Humeral Mass: A Rare Case Presentation

Abstract Follicular thyroid carcinoma is the second most common cancer of the thyroid, which usually presents as a solitary thyroid nodule. Diagnosis of follicular thyroid cancer involving the appendicular skeleton is very rare. In this paper, we report a case of a 65-year-old woman who previously underwent partial lobectomy of the left thyroid gland, and who consequently presented with a 2-year history of gradually enlarging left arm mass. Initial whole-body bone imaging revealed a large osteolytic lesion in the humerus. An MRI (magnetic resonance imaging) of the left arm showed a heterogeneously enhancing, encapsulated, soft tissue mass with humeral involvement, and the initial impression was osteosarcoma versus fibrosarcoma. Biopsy reading of the humeral mass was morphologically compatible with a well-differentiated metastatic thyroid carcinoma. She subsequently underwent right lobectomy where histopathology showed Hashimoto’s thyroiditis. A slide review was requested and the biopsy of the humeral mass revealed adenocarcinoma with follicular architecture, compatible with a metastatic thyroid carcinoma. Meanwhile, the findings on the right thyroid lobe revealed a multinodular colloid adenomatous goiter with hyperplastic features in a background of Hashimoto’s thyroiditis. This report demonstrated a rare presentation of follicular thyroid carcinoma metastasizing to the humerus that can be confused with primary bone tumors, both clinically and radiologically. Early diagnosis and a high index of suspicion is foremost for immediate and appropriate management.