Identifying Thyroid Follicular Proliferations that Need Lobectomy; value of the Bethesda Category 4

Abstract

Introduction: Thyroid follicular proliferations (TFPs) identified on fine needle aspiration cytology can be either follicular lesions of undetermined significance; Bethesda category 3 or follicular neoplasms and lesions suspicious for a follicular neoplasm; Bethesda category 4. The purpose of categorizing to Bethesda category 4 is to identify a thyroid nodule that might be a follicular carcinoma and triage it for thyroid lobectomy. This study was designed to determine the predictive value of categorizing TFPs to Bethesda category 4 in deciding on lobectomy for cytologically identified TFPs.

Methods: This retrospective study included all patients with TFPs identified on cytology, and had a subsequent histological diagnosis, at our unit, over a period of two years. TFPs were categorized into either Bethesda category 3 or 4 on cytology, according to the Bethesda system. Sensitivity, specificity and positive (PPV) and negative predictive values (NPV) for Bethesda category 4 in identifying neoplastic TFPs and implied risk of malignancy for Bethesda category 3 and 4 were calculated taking histopathology as the gold standard. A total of 52 TFPs (Bethesda category 3; n = 39, Bethesda category 4; n = 13) were included. Subsequent histology has confirmed 18 neoplastic and 34 non-neoplastic TFPs. Sensitivity and specificity of Bethesda category 4 in identifying neoplastic TFPs were 66.66% and 97.05% respectively. PPV and NPV of Bethesda category 4 were 92.3% and 84.6% respectively. Implied risk of malignancy for Bethesda category 3 and 4 were 5.12% and 15.38% respectively.

Conclusions: Bethesda category 4 predicts the TFPs that need thyroid lobectomy to triage for follicular carcinoma. The Bethesda category 3 and 4 carry an implied risk of malignancy comparable to the expected values given in Bethesda system.