Fine-needle aspiration biopsy cytology of hyalinizing trabecular adenomas of the thyroid.

Cytologic smears from fine-needle aspirates of three histologically and ultrastructurally confirmed hyalinizing trabecular adenomas of the thyroid (HTAT) were reviewed. In two cases a cytodiagnosis of HTAT was suggested, and in one patient a diagnosis of trabecular epithelial neoplasm was made. In all three cases, small clusters and sheets of epithelial cells with abundant, filamentous, vacuolated, and ill-defined cytoplasm were present. The nuclei were slightly pleomorphic and showed nuclear overlapping, nuclear grooves, and intranuclear cytoplasmic inclusions. Small and irregular fragments of acellular hyalinized material (AHM) were noted within the tumor cell clusters in the first two cases. In the third patient, large syncytial sheets and anastomotic cords of epithelial cells showing ill-defined, filamentous cytoplasm, slightly pleomorphic nuclei, nuclear overlapping, intranuclear cytoplasmic inclusions, and nuclear grooves were present. Fragments of AHM were not observed within clusters and syncytial sheets of tumor cells.