Clue helping to distinguish hyalinizing trabecular adenoma from carcinoma of the thyroid in fine-needle aspirates.

Fine-needle aspirates from four hyalinizing trabecular thyroid adenomas stained with May-Grünwald-Giemsa showed a distinctive component of purplish red stromal deposits corresponding to accumulations of basement membrane material occurring in such tumors. Recognition of these deposits helps to prevent cytologic overdiagnosis of malignancy in this rare benign tumor, which has a number of traits in common with both papillary and medullary carcinoma of the thyroid.