Evaluating the diagnostic significance of nuclear grooves in thyroid fine needle aspirates with a semiquantitative approach.

OBJECTIVE To clarify the diagnostic significance of nuclear grooves in thyroid fine needle aspirates, to search for other associated nuclear features and to identify possible diagnostic pitfalls. STUDY DESIGN In total, 67 fine needle aspiration cases were retrospectively reviewed for selected nuclear features, including grooves, intranuclear cytoplasmic invaginations, enlargement, pleomorphism and status of nucleoli. A semiquantitative method was used to estimate the percentage of nuclear grooves in 5 high-power fields with the most frequent nuclear grooves. RESULTS Unequivocal intranuclear cytoplasmic invaginations were a specific diagnostic feature of papillary carcinoma. In the absence of intranuclear cytoplasmic invaginations, the presence of > or = 20% nuclear grooves was virtually diagnostic of thyroid neoplasms, predominantly papillary carcinoma. Less than 10% of nuclear grooves virtually eliminated the possibility of papillary carcinoma. However, 10-19% of nuclear grooves may be seen in papillary carcinoma and benign lesions; therefore, such cases fell into the diagnostic category of "atypical cytology" or "indeterminate" cytology. Nuclear enlargement with elongation was a readily identifiable feature usually associated with nuclear grooves. Significant pleomorphism was more commonly seen in papillary carcinoma than in benign lesions. CONCLUSION A semiquantitative method is helpful when nuclear grooves are encountered in thyroid cytology in the absence of other diagnostic features. It can significantly improve the diagnostic specificity of nuclear grooves for papillary carcinoma.