Risk factors associated with malignancy and with triage to surgery in thyroid nodules classified as Bethesda category IV (FN/SFN)

Background

Thyroid nodules diagnosed as Bethesda category IV [follicular neoplasm/suspicious for follicular neoplasm (FN/SFN)] are recommended for surgery. However, only 10%-40% of these nodules turn out to be malignant on histopathological examination. Therefore, selection for surgery of nodules diagnosed as Bethesda category IV is important. We aimed to define predictive factors for malignancy and factors associated with triage to surgery.

Methods

The records of all patients with nodules who underwent fine needle aspiration biopsy (FNAB) and classified by Bethesda reporting system as FN/SFN between January 2011 and July 2017 at our institution were reviewed. Univariate and multivariate analysis were performed to select independent factors associated with thyroid cancer, and with triage to surgery. Using independent risk factors for malignancy predictive index categories were created.

Results

Among 6910 nodules that underwent FNAB, 180 (2.6%) were diagnosed as FN/SFN. Of the 180 patients, 139 (77%) underwent surgery with the associated malignancy rate of 37% (51/139) (upper boundary). Risk of malignancy among all FN/SFN nodules was 28% (lower boundary). Solid structure, size ≥ 4 cm, microcalcification, hypoechogenicity, and increased vascularization were found to be significant and independent risk factors associated for malignancy. None of the clinical and ultrasound factors were associated with triage to surgery.

Conclusions

Our findings showed that using predictive factors for malignancy in the Bethesda IV category as risk indices, 17% of patients who had nodules without any risk factors could be spared surgery. Predictive indices could be considered for the malignancy risk and for selection of patients for surgery.

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