Correlation between indeterminate aspiration cytology and final histopathology of thyroid neoplasms

Of all thyroid nodules assessed by fine needle aspiration cytology (FNAC), 10-20% are classified as indeterminate/atypical. Traditionally, this group is considered to primarily represent follicular neoplasia. We hypothesize that papillary carcinoma accounts for a significant proportion of lesions classified as "atypical" on FNAC.

This retrospective study includes 228 patients who had an atypical FNAC result and who were subsequently found to have a malignancy on histologic examination of the excised thyroid lesion. Patients with papillary microcarcinomas, defined as lesions less than 10-mm diameter, were excluded. The study period was from 1987 to 2005. The patients were divided chronologically into 3 groups (n = 76) for analysis: group 1, December 1987-March 1997; group 2, July 1997-October 2002; and group 3, October 2002-December 2005.

Age- and sex-distribution of the 3 groups were not significantly different. Median nodule size of group 3 was significantly smaller. The distributions of histopathology of the 3 time periods were significantly different overall (P = .0325). Prevalence of papillary carcinoma was not statistically significant (33/76 vs 34/76 vs 46/76; P = .0636), but showed a statistical significant trend to increase over time (P = .0349). Prevalence of follicular variant papillary carcinoma was also found to be significantly different between the groups (7/76 vs 12/76 vs 19/76; P = .0320; P = .0349).

Papillary carcinoma accounted for most histopathologically confirmed cancers that had an atypical cytology. Papillary cancer in this group of patients trended up, probably due to a significant increase in the diagnosis of follicular variant of papillary cancer.