The significance of the grooved nucleus in thyroid lesions

Nuclear grooving has recently been accepted as a useful diagnostic criterion for papillary thyroid carcinoma. In order to determine whether this feature can serve as a reliable cytomorphologic marker of papillary carcinoma we studied, by light microscope, the surgical specimens of 80 nonpapillary thyroid lesions including 35 follicular adenomas, 8 follicular carcinomas, 5 Hürthle cell adenomas, 4 Hürthle cell carcinomas, 4 medullary carcinomas, 2 undifferentiated carcinomas, 5 cases of Hashimoto's thyroiditis, 5 diffuse hyperplasias, 2 adenomatous hyperplasias, and 10 nodular goiters. In each case, 10 random high-power fields (HPF) per slide were reviewed and the frequency of grooved nuclei per microscopic field examined and recorded. Nuclear grooves were found in all but 11 cases (one case of adenomatous hyperplasia and 10 cases of nodular goiter). Overall, 40% of the nonpapillary thyroid lesions contained nuclear grooves in more than 9 HPFs, 42% in 5 to 8 HPFs and 18% in less than 4 HPFs. Twenty four percent of the nonpapillary neoplastic lesions had eight or more grooved nuclei per HPF and 76% had six or less. The latter frequency was recorded for the 50% of the nonneoplastic thyroid conditions. Occasional intranuclear inclusions were seen in two cases of follicular tumors and in one case of Hürthle cell carcinoma. It is apparent from this study that nuclear grooving is not necessarily restricted to papillary thyroid cancer, and that it can be present in a variety of other thyroid lesions.