Cytologic features of fine-needle aspirates of hyalinizing trabecular adenoma of the thyroid.

The cytologic features of five cases of hyalinizing trabecular adenoma of the thyroid are reviewed. All of these cases had been initially interpreted as either suspicious or positive for malignancy. On retrospective review, many of the cytologic features did mimic those of other lesions, particularly papillary carcinoma. The smears tended to hypercellularity, and nuclei were often slightly enlarged with pale chromatin, intranuclear holes, and longitudinal grooving of the nuclear membrane. On the other hand, some cytologic features were more suggestive of medullary carcinoma--poor cohesion of cells with elongated and spindle cell forms and hyaline acellular areas. Awareness of the histologic and cytologic features of hyalinizing trabecular adenoma may enable the cytopathologist to avoid a false positive diagnosis of papillary carcinoma or medullary carcinoma, although it is unrealistic to expect a definitive diagnosis of hyalinizing trabecular adenoma.