Evidence-based criteria for adequacy in thyroid fine-needle aspiration.

To determine whether some thyroid fine-needle aspirates classified as nondiagnostic correlate with benign thyroid nodules and can be distinguished from other nondiagnostic aspirates, I reviewed (from a total of 1,581) 80 nondiagnostic cases, all of which were hypocellular and lacked colloid, and correlated the cytologic findings with the results of pathologic follow-up. Of the 80, 16 had carcinoma at follow-up and 64 were benign. The cellularity of the carcinoma cases ranged from 0 to 100 cells (mean, 20 cells), but every case with epithelial cells had Hürthle cell change or atypia suggestive of papillary carcinoma. The cellularity of the 64 benign cases ranged from 0 to 120 cells (mean, 40 cells), 17 of which had Hürthle cell change. There were 25 cases with at least 10 benign-appearing follicular cells without atypia or Hürthle cell change; all 25 cases were associated with benign follow-up. While these results need to be confirmed by others, the evidence suggests that a proportion of thyroid aspirates that do not meet traditional criteria for adequacy still may be associated strongly with a benign thyroid nodule and can be distinguished from other nondiagnostic aspirates.