Hyalinizing Trabecular Adenoma of Thyroid

ABSTRACT

The Hyalinizing trabecular adenoma of the thyroid is a uncommon benign neoplasm which is characterized by trabecular growth pattern with hyaline stroma of the basal membrane type. It is often misdiagnosed as papillary carcinoma due to its peculiar cytologic and histologic features such as, nuclear grooving and papillary structures, or as medullary carcinoma due to the hyalinized stroma resembling amyloid. Special stains and immunohistochemical studies are required to make a definite diagnosis. A 34-year old woman was admitted suffering from a left neck mass. Computed tomography showed a 2 cm-sized mass in the left thyroid. Fine needle aspiration cytology suggested papillary carcinoma. Intraoperative frozen section suggested medullary carcinoma, and H&E staining suggested medullary carcinoma. However according to immunohistochemistry which revealed calcitonin negative, the tumor was reviewed and finally diagnosed as hyaline trabecular adenoma. The hyalinizing trabecular adenoma, although uncommon, is certainly worth consideration in order to avoid being misinterpreted as carcinoma on the basis of individual cytologic and histologic features.