Hyalinizing trabecular adenoma of the thyroid gland: Cytologic features in 29 cases

Cytologic material (fine-needle aspiration biopsy smears, thin-layer preparations, cell block sections, and touch preparations) from 29 cases of hyalinizing trabecular adenoma was studied to 1) establish the cytologic profile of the neoplasm and 2) compare the profile with those of papillary and medullary carcinoma. Papanicolaou- and Diff-Quik-stained smears of the hyalinizing trabecular adenomas were uniformly bloody. The smears featured cells in cohesive aggregates radially oriented around hyaline material, less frequently, singly. Cytoplasm was abundant, and the nucleocytoplasmic ratio was low. Intranuclear cytoplasmic inclusions, nuclear grooves, and nuclear overlapping were very common and best seen with the Papanicolaou method. Diff-Quik-stained smears highlighted the hyaline material (metachromatic), perinucleolar clearing, and cytoplasmic bodies. The combination of a bloody background, radially oriented cohesive cells, cells with abundant cytoplasm, nuclei with very frequent cytoplasmic inclusions and grooves, and the presence of hyalin should suggest the presence of hyalinizing trabecular adenoma.