Introduction: The hyalinizing trabecular tumor is a rare, benign neoplasm of the thyroid gland, often posing a diagnostic challenge due to its cytological resemblance to more aggressive thyroid malignancies. This study aims to identify cytological features that can differentiate hyalinizing trabecular tumors from other thyroid neoplasms, thereby preventing unnecessary total thyroidectomies.

Material and Methods: We conducted a retrospective analysis of six hyalinizing trabecular tumor cases diagnosed at the Hospital Clínico San Carlos in Madrid, Spain, over the past decade. Cytological specimens were thoroughly reviewed.

Results: The presence of hyaline material in fine needle aspiration (FNA) specimens emerged as a consistent diagnostic indicator for hyalinizing trabecular tumors. However, it is crucial to differentiate this hyaline material from dense colloid or amyloid, which is characteristic of Medullary Carcinoma. Notably, hyalinizing trabecular tumors lack papillary architecture and fibrovascular cores. Ancillary tests, such as ki-67, calcitonin, and Congo Red staining, proved valuable in confirming the diagnosis.

Conclusion: Cytopathologists should familiarize themselves with the distinguishing features of hyalinizing trabecular tumors, especially the characteristic hyaline material, to facilitate accurate diagnosis and reduce the unnecessary aggressive management of affected patients.