Association of ultrasonographically determined anatomical location of Bethesda 3 thyroid nodules with differentiated thyroid cancer

Background: The size of a thyroid nodule and certain sonographic features, such as marked hypoechogenicity, microcalcifications, taller-than-wide shape, microlobulated, or irregular margins, indicate the greater malignancy risk. The frequency of the atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) category among cytology reports from thyroid fine-needle aspirations ranges from 0.8% to 28%, whereas the risk of malignancy of these nodules varies from 6% to 97%. This retrospective analysis investigated whether the preoperative ultrasonographic location of Bethesda 3 thyroid nodules is a predictive risk factor for differentiated thyroid cancer (DTC). Methods: A total of 387 patients who underwent total thyroidectomy for a nodule with AUS/FLUS cytology and diagnosed with a DTC at five tertiary referral centers between 2010 and 2020 were retrospectively analyzed. The location of the thyroid nodule with AUS/FLUS cytology was categorized into two groups: one group was composed of the isthmus, upper lobe, middle lobe, and lower lobe, whereas the latter consisted of right lobe, left lobe, and isthmus. Results: DTC was diagnosed in 40.6% (n = 157) of the operated nodules. Multiple logistic regression analysis has revealed that hypoechogenicity of the nodule (odds ratio [OR] = 2.929, p < 0.001) was the only independent predictive factor for the malignancy of the nodules with AUS/FLUS, whereas the location of the nodule, age, and sex were not significantly independent risk factors. Multifocality and contralateral benign nodules were independent predictive factors for multicentricity (OR = 3.5, p = 0.002; OR = 5.5, p = 0.001, respectively). Conclusion: As the first study investigating the association between a Bethesda 3 nodule location and the risk of malignancy by evaluating postoperative cytology reports, the results showed that nodule location with AUS/FLUS on fine-needle aspiration biopsy was not a predictive risk factor for the diagnosis of DTC.