A challenging case of Mesenchymal Chondrosarcoma involving the thyroid and special considerations for diagnosis.

Background: Thyroid ultrasound is usually used to risk-stratify incidental thyroid nodules. Nodules with high risk sonographic features for malignancy are evaluated by fine-needle aspiration. The role of core needle biopsy for thyroid nodules is limited to cases where the fine needle aspiration is inconclusive.

Case presentation: We describe a rare case of mesenchymal chondrosarcoma of the thyroid gland with uncertain primary origin. Thyroid ultrasound showed right sided large, solid, hypoechoic nodule with calcifications and peripheral vascularity and unremarkable isthmus and left thyroid lobe. Fine needle aspiration of the right nodule suggested lymphocytic thyroiditis. The sonographic findings contradicted the typical bilateral clinical and sonographic picture of lymphocytic thyroiditis. A core needle biopsy showed mesenchymal chondrosarcoma.

Conclusion: This case highlights the importance of correlating pathologic diagnosis with sonographic findings, the appropriate utilization of fine needle aspiration and core needle biopsy to evaluate thyroid nodules and the rare incidence of mesenchymal chondrosarcoma involving the thyroid.