Abstract
A hyalinizing trabecular tumor (HTT) is a rare and controversial thyroid gland tumor with an extremely low malignant potential. Its cytological and histological features overlap with those of papillary thyroid carcinomas (PTCs) and medullary thyroid carcinomas (MTCs). Hence, diagnosis of this entity can be challenging, especially when diagnosis is based on fine needle aspiration cytology (FNAC). Herein, we report the case of a 52-year-old woman with HTT along with the cytological, histological and immunohistochemical studies performed. A follicular origin for the tumor was confirmed based on immunohistochemistry, which showed that the tumor cells were positive for thyroglobulin and TTF-1 and negative for calcitonin. The tumor cells were also negative for HBME-1, galactin-3 and CK19, but they were positive for CD56. The preferred diagnosis based on the histological and immunohistochemistry studies was an HTT. The patient is currently undergoing regular follow-up visits and has shown no evidence of residual tumor or metastasis. This case highlights the importance of considering HTT when interpreting FNAC results when the cytological features are those of PTC or MTC, but the ultrasonography findings are not worrisome.