What Is a Significant Nuclear Groove in Thyroid Fine Needle Aspiration Cytology?

Abstract

Background: Nuclear grooves are an important diagnostic feature in thyroid fine needle aspiration (FNA). However, their exact role remains undefined.

Materials and methods: This study includes both retrospective and prospective analyses of the significance of identifying and counting deep grooves under low-power magnification (20×) in Pap-stained cytology smears for the classification of thyroid FNA results and, consequently, patient management.

Result: Two cut-off points have been identified to stratify thyroid smears into three categories: benign with no grooves identified, 1-9 grooves in indeterminate cases, and ≥ 10 grooves in papillary thyroid carcinoma (PTC). Deep groove identification and counting under 20× magnification are highly reproducible between observers (K = 0.61). Using groove-based criteria instead of the archival Bethesda System for Reporting Thyroid Cytology (BSRTC) leads to a significantly higher diagnosis of follicular adenomas as benign (p < 0.0001), with fewer noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP) categorized as benign (p = 0.002). The follicular variant of papillary carcinomas (FV-PTC), previously considered indeterminate, showed a significant decline (p < 0.001), and false-negative diagnoses of PTC and FV-PTC were eliminated. A significant difference favoring the groove-based approach was noted regarding specificity and positive (PLR) and negative (NLR) likelihood ratios (p = 0.0014). Finally, a substantial reduction in the false-negative rate was observed prospectively (p = 0.0014). The number of unnecessary surgeries among benign cases has decreased.

Conclusion: Incorporating the presence and frequency of deep nuclear grooves seen at 20× magnification improves the outcome of thyroid FNA classification and overall patient management.