Interobserver Concordance in The Bethesda System Categorization of Thyroid Nodules: A Critical Evaluation

Abstract

Background: The Bethesda System for Reporting Thyroid Cytopathology 2023  (TBSRTC) offers a standardized, economical diagnostic approach. The maintenance of reproducibility of the TBSRTC categories in spite of interobserver variability is critical. In this study, interobserver diagnostic consistency and reproducibility were evaluated alongside category distribution to assess the institutional diagnostic reliability.

Methods: This cross-sectional, observational, hospital-based retrospective study was carried out over a period of 2-year. Cases of thyroid nodules undergoing FNAC were reviewed and categorized according to the TBSRTC (2023) guidelines. To evaluate interobserver concordance, two cytopathologists independently reviewed the smears.

Results: A total of 82 cases were analysed. The mean age was 36.91 (± 10.82) years with a distinct female predominance (F: M ratio of 19.2:1). The majority of cases (62 cases, 75.6%) were benign (Bethesda Category II), followed by 12 cases (14.6%) of Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance (AUS/FLUS; Category III). Follicular Neoplasm/Suspicious for a Follicular Neoplasm (Category IV) was reported in 3 cases (3.7%), 2 cases (2.4%) were Suspicious for Malignancy (Category V), and 1 case (1.2%) was diagnosed as Malignant (Category VI). Interobserver concordance was highest in the benign group (Category II), yielding a 95.2% absolute agreement, while the highest variability was concentrated within the indeterminate cohorts (Categories III and IV).

Conclusion: High interobserver concordance observed in this study underscores the reproducibility and diagnostic reliability of the Bethesda System in routine thyroid cytopathology practice. Interobserver validation may serve as an important quality assurance measure in institutions where comprehensive cytohistological follow-up is limited.