Intrathyroidal thymic carcinoma exhibiting neuroendocrine differentiation: Case report with cytomorphology, immunocytochemistry, and review of the literature focusing on cytology.

Intrathyroidal thymic carcinoma is a malignant epithelial tumor of the thyroid gland with thymic epithelial differentiation; it is the malignant counterpart of ectopic thymoma of the thyroid gland and histologically resembles thymic carcinoma. Given its favorable prognostic course, preoperative cytological diagnosis is important to distinguish this neoplasm from other more aggressive thyroid neoplasms that can have similar or overlapping cytomorphological features. However, there is little information about the cytology of this disease available in the literature, even in the latest fourth edition of World Health Organization classification of tumors of endocrine organs. Here, we report a case of intrathyroidal thymic carcinoma exhibiting neuroendocrine differentiation in a 33-year-old woman and present a review of the literature.