Abstract

Columnar Cell subtype of Papillary Thyroid Carcinoma (CC-PTC) is an exceptionally rare histologic subtype, accounting for less than 0.5% of all papillary thyroid carcinomas worldwide.¹,² Despite its rarity, CC-PTC demonstrates aggressive biological behavior and is classified as a high-risk histologic subtype in the World Health Organization Classification of Tumors of Endocrine Organs, 5th Edition (2022)³, owing to its frequent association with capsular invasion, lymph vascular permeation, extrathyroidal extension, and distant metastasis. The tumor poses significant diagnostic challenges due to its distinctive morphology, particularly on cytology and limited biopsy material.4,6 Case Presentation: A 27-year-old woman presented with a one-year history of anterior neck swelling with recent onset throat pain. ltrasonography revealed a right thyroid lobe nodule categorized as TI-RADS 4/5. Fine-needle aspiration cytology showed highly cellular smears composed of tall and columnar epithelial cells arranged in papillary fragments and sheets, exhibiting nuclear elongation, hyperchromatic nuclei, marked pseudo stratification, and occasional nuclear pseudoinclusions, consistent with Bethesda Category VI. Total thyroidectomy revealed a 3-cm ill-defined, unencapsulated grey-white tumor. Histopathological and Immunohistochemical Findings: Histopathology demonstrated circumscribed tumor composed of complex papillary and trabecular architecture lined by pseudostratified columnar cells with elongated hyperchromatic nuclei, conspicuous eosinophilic nucleoli, amphophilic cytoplasm, increased mitotic activity, and extensive lymphovascular invasion. Immunohistochemistry confirmed thyroid follicular epithelial origin with tumor cell nuclear positivity for TTF-1 and retained membranous β-catenin expression, while CDX2 was negative. A high Ki-67 labelling index supported the aggressive proliferative nature of the tumor. Conclusion: This case highlights the importance of recognizing the distinctive cytomorphologic, histopathologic and immunohistochemical features of CC-PTC. Accurate diagnosis requires a multimodal approach integrating clinical findings, cytology, histopathology, and immunohistochemistry, particularly in young patients where aggressive behavior may be unsuspected.

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