Cytologic Features and BRAF Mutation of Hyalinizing Trabecular Adenoma of the Thyroid - A Case Report with Review of the Literature -

Hyalinizing trabecular adenoma (HTA) of the thyroid, characterized by the presence of a trabecular-alveolar growth pattern and marked intratrabecular hyalinization, was initially described 100 years ago. In 1987, Carney et al. introduced the term HTA to describe this rare tumor of the thyroid composed of polygonal, oval, and spindle cells arranged in a trabecular pattern and separated by a hyalinized stroma. The most important aspect of HTA is that it can resemble other thyroid malignancies both cytologically and histopathologically, specifically, papillary and medullary carcinomas. The nuclear characteristics of HTA result in confusion with papillary thyroid carcinoma (PTC), and hyaline material does with that of medullary thyroid carcinoma (MTC). These misinterpretations may result in unnecessary or aggressive surgical management. In practice, fine needle aspiration cytology (FNAC) is the best tool for preoperatively evaluating the thyroid nodules. Cytological features of HTA have been reported, and Casey et al. described a detailed cytological profile of HTA compared with that of PTC and MTC. However, HTA is frequently misinterpreted by FNAC as PTC and sometimes diagnosed as MTC or atypical cells. In contrast to the cytological similarities between HTA and PTC, there are distinct differences among many studies detailing the prevalence of the BRAF gene. Recently, we experienced a case of HTA in a 49-year-old woman. Here, we report the cytological features of HTA correlated with the histopathological findings and a briefly review of the Korean literature. Additionally, we present results of a BRAF gene mutation analysis for three HTA cases, including another two tumors from a different institution.