Abstract
Introduction/Objective
Thyroid carcinoma showing thymus-like differentiation also known as intrathyroidal thymic carcinoma is a rare thyroid neoplasm arising from either an ectopic intrathyroidal thymic tissue or from remnants of thymobranchial pouches. On fine needle aspiration (FNA) its diagnosis can be challenging due to overlapping morphologic features with other aggressive thyroid carcinomas.
Methods/Case Report
A 31-year-old female consulted for 6-month history of neck swelling and tenderness. Thyroid ultrasound demonstrated a 2.6 x 2.5 x 2.1 cm nodule in the right lobe with punctate calcifications. FNA showed cellular smears composed of loosely cohesive and single basaloid neoplastic cells exhibiting significant cellular and nuclear pleomorphism. Focal squamous differentiation with keratinization was noted on the cell block sections. Immunocytochemical stains showed that the tumor was positive for cytokeratin AE1/AE3, p40, p63, CD117 and CD5 consistent with intrathyroidal thymic carcinoma. The Ki67 proliferative index was approximately 40%. A right thyroidectomy with central neck dissection confirmed the diagnosis and showed a 3.0 cm tumor with invasion into skeletal muscle, lymphovascular invasion and positive lymph nodes. The patient completed adjuvant radiotherapy and remain in remission at 3-months follow-up.
Results (if a Case Study enter NA)
NA
Conclusion
Intrathyroidal thymic carcinoma is a rare thyroid neoplasm that frequently shows squamous differentiation and therefore overlaps with papillary thyroid carcinoma with squamous morulae, squamous cell carcinoma and anaplastic carcinoma. The coexpression of squamous markers together with CD5 and CD117 allows the recognition of CASTLE on FNA samples.
Fine‐needle aspiration cytology of metastatic spindle cell follicular thyroid carcinoma: A case report
