Should "indeterminate" diagnoses be used for thyroid fine-needle aspirates of nodules smaller than 1 cm?

The Bethesda System for thyroid fine-needle aspirates does not account for the size of the lesion that is aspirated.

To determine whether the size of the lesion would be helpful in order to reduce indeterminate thyroid aspirations.

We correlated the results of all thyroid aspirations and surgical resection for the last 16 years at our institutions.

A total of 9080 cases were aspirated and 1393 resections were performed. Of those resected, a total of 236 (17%) were classified as atypical follicular cells of undetermined significance, and 256 (18%) were classified as suspicious for a follicular/Hürthle cell neoplasm. A total of 52 incidental papillary carcinomas were identified in these indeterminate cases at resection (52 of 492; 11%). Thirty-seven (16%) atypical follicular cells of undetermined significance cases and 21 (8%) suspicious for a follicular/Hürthle cell neoplasm cases were for nodules smaller than 1 cm in diameter. When cases subtyped as atypical, a papillary carcinoma cannot be ruled out, were removed (13 cases), the remaining 24 and 21 aspirates identified 3 tumors each (13% and 14%), all papillary carcinomas. Together, the incidence of identified carcinomas was not significantly different than that of incidental carcinomas (13% versus 11%, P = .48). The rate of identified carcinomas was significantly less than for similar indeterminate cases smaller than 1 cm (excluding cases of atypical, papillary carcinoma cannot be ruled out) (88 of 330 cases; 27%; P = .05).

For nodules smaller than 1 cm in our series, indeterminate aspirates without features of papillary carcinomas have the same risk of malignancy as benign aspirates.