Prevalence and associated malignancy of Bethesda category III cytologies of thyroid nodules assigned to the "cytological atypia" or "architectural atypia" groups.

OBJECTIVE

To ascertain the prevalence of Bethesda category III cytologies and their malignancy rate, and to analyze differences in the second cytology, malignancy rate, type of carcinoma, and TNM stage between the cytological atypia (CA) and architectural atypia (AA) groups.

PATIENTS AND METHOD

A retrospective study of 973 biopsies. Bethesda category III cytologies were classified as CA when nuclear atypia was seen but they were not diagnostic or suspicious of malignancy, and as AA when smears had few cells but had a predominantly microfollicular pattern and minimal or absent colloid. The cytological and pathological results were correlated.

RESULTS

There were 87 (8.9%) Bethesda category III cytologies (34 CC, 53 AA). Second cytologies were performed in 23 patients (16 with CA, 7 with AA), and a benign result was found in 68.7% of CA and 71.4% of the AA group. Sixty-four patients (23 CA, 41 AA) underwent surgery and 15 of these (23.4%) had a malignant disease: 39.1% CA vs 14.6% AA (P=.029). There was a false negative result in the CA group. The follicular variant of papillary thyroid carcinoma was the most common malignancy (60%). There were no differences in type of carcinoma or TNM stage between CA and AA patients.

CONCLUSIONS

The reported prevalence of Bethesda category III cytologies was as expected. The malignancy rate was significantly higher in the CA group, but there were no differences in the result of the second cytology, type of carcinoma found, or TNM stage. The division of Bethesda category III cytologies is useful to provide a better stratification of the risk of malignancy.