Diagnostic Lobectomy for Bethesda III Thyroid Nodules: Pathological Outcomes and Risk Factors for Malignancy

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• Indeterminate thyroid nodules, classified under the Bethesda system as AUS/FLUS (atypical cells or follicular lesion of undetermined significance), pose a diagnostic challenge.
• Fine-needle aspiration (FNA) is the primary diagnostic tool, but Bethesda III nodules require careful management due to uncertain malignancy risk.

Purpose of the Study:

• To evaluate the institutional experience with Bethesda III thyroid nodules.
• To determine the risk of malignancy (ROM) for nodules removed via diagnostic lobectomy.
• To identify radiologic and clinical risk factors associated with malignancy in Bethesda III nodules.

Main Methods:

• Retrospective chart review of patients with Bethesda III thyroid FNA at San Antonio Military Medical Center from 2010 to 2018.
• Analysis of 183 lobectomies performed for AUS/FLUS nodules to determine final histological diagnosis.
• Statistical evaluation (chi-square, Wilcoxon rank-sum tests) of clinical and radiologic factors, including age, BMI, nodule size, and family history, for association with malignancy.

Main Results:

• Of 183 lobectomies for AUS/FLUS nodules, 38.3% were malignant.
• Repeat FNA in 52% of cases did not significantly alter the Bethesda classification, with 90% remaining Bethesda II or III.
• Age under 30 was the only statistically significant factor associated with an increased risk of malignancy (P=0.04).

Conclusions:

• The actual risk of malignancy for indeterminate thyroid nodules (Bethesda III) may be higher than often presumed.
• Younger patient age (<30 years) appears to be a more reliable indicator of malignancy risk compared to repeat FNA results in Bethesda III nodules.