The 4-cm threshold and malignancy yield in surgically treated Bethesda IV thyroid nodules
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Fabio Medas1, Federico Cappellacci1, Gian Luigi Canu1
1Department of Surgical Sciences, University of Cagliari, SS 554, Cittadella Universitaria di Monserrato, 09042, Monserrato, CA, Italy.
Introduction:
We examined whether the 40-mm threshold identifies a higher malignant proportion among surgically treated Bethesda IV nodules.
Materials And Methods:
This single-center retrospective cohort included adults with a recorded ultrasound diameter and assignable final histology. All cytology was assessed by the same cytopathologist. Diameter was analysed continuously, with a restricted cubic spline, and at 40 mm. Additional models included recorded ultrasound features. Carcinoma characteristics were examined once per patient as exploratory outcomes.
Results:
The cohort comprised 676 nodules from 644 operations in 643 patients; 219 were malignant (32.4%). The malignant proportion was 28.8% at ≥40 mm and 33.2% below 40 mm (difference, -4.3% (95% CI, -12.8 to 5.2); adjusted OR, 0.80 (0.50-1.27)). The relation with diameter was nonlinear (P < 0.001). Among 627 nodules with recorded echogenicity, the OR after adding hypoechogenicity was 0.83 (0.51-1.36). In the exploratory analysis of 210 patients with differentiated thyroid carcinoma, adverse pathology occurred in 16/34 cancers ≥40 mm and 55/176 smaller cancers, largely reflecting angioinvasion (15/34 vs 15/176).
Conclusion:
The 40-mm comparison did not demonstrate a higher malignant proportion within this surgical cohort; equivalence was not established. The secondary angioinvasion finding requires confirmation. These data do not establish the comparative benefits of different operations.