Thyroid fine-needle aspiration with atypia of undetermined significance: a necessary or optional category?

Atypia of undetermined significance is a controversial category in thyroid fine-needle aspiration (FNA), not only for its questioned clinical utility, but also for its very existence as an expression of uncertainty. The current study was performed to investigate the potential impact of eliminating this category on the sensitivity and specificity for detecting thyroid neoplasms by FNA.

Forty cases originally diagnosed as atypia of undetermined significance with histologic follow-up were selected for the present study. These cases were reinterpreted blindly by 2 experienced reviewers, who eliminated atypia of undetermined significance as a diagnostic possibility and reclassified these cases as either benign, follicular neoplasm, suspicious for malignancy, or malignant. Twenty-six cases of atypia of undetermined significance were randomly selected and reevaluated 6 months later to study intraobserver variation.

After eliminating the atypia of undetermined significance category, the sensitivity for detecting papillary thyroid carcinoma (PTC) was reduced from 100% to 27% (P = .04). In those atypia of undetermined significance cases that were reclassified as benign, 37% had PTC. In those reclassified as follicular neoplasm or suspicious for malignancy, 38% were histologically proven to be benign lesions. Unanimous interobserver and intraobserver agreement was observed in only 60% of cases.

Eliminating the diagnosis of atypia of undetermined significance substantially decreases the sensitivity of thyroid FNAs and increases both false-positive and false-negative rates. In addition, it increases interobserver and intraobserver variability. Therefore, the atypia of undetermined significance category should not be eliminated; but we advocate minimizing its use.