A tertiary center's experience with second review of 3885 thyroid cytopathology specimens.

Background: Although the Bethesda System for Reporting Thyroid Cytopathology (BSRTC) has standardized the diagnostic terminology for thyroid fine-needle aspiration (FNA), morphological interpretation remains subjective, and interobserver discrepancies are expected. This study quantifies the frequency and magnitude of these discrepancies in a single tertiary center's experience and elucidates key factors that are associated with changes in diagnosis.

Methods: Institutional consultation for 3885 thyroid cytological samples over 45 months were reviewed. BSRTC classification made by the sending institution was compared with that of our institution. An ANOVA was performed to determine factors that may be associated with interinstitutional diagnostic differences. Histopathology diagnoses were available for 1049 (27%) nodules; the malignancy rates for inside and outside BSRTC classifications were calculated.

Results: There were 937 1-step changes and 301 ≥2-step diagnostic discrepancies comprising 24% and 8% of all cases, respectively. Second review decreased the indeterminate rate 38% to 28% (P < .000001). Indeterminate diagnostic category before second review, low specimen cellularity, Hashimoto's thyroiditis, and low volume of consults from the sending institution were associated with discordance. Of the 1049 thyroid nodules operated for which unequivocal histopathology was available, the malignancy rates for the BSRTC categories before and after second review were compared. Categorical upgrades were associated with a malignancy rate of 84%, whereas downgrades were associated with a malignancy rate of 38% (P < .000001).

Conclusion: This is the largest series to date of thyroid cytology second review. The BSRTC classification changed 32% of the time, potentially resulting in significant changes in clinical and surgical management. Because certain specimen characteristics (indeterminate diagnostic category before second review, low specimen cellularity, Hashimoto's thyroiditis, and low volume of consults from the sending institution) were particularly associated with a diagnosis change, morphological second review may be of potential benefit in these settings.