Fine Needle Aspiration Biopsy (FNAB) is accepted as a precise, safe, and cost-effective tool for diagnosis of the thyroid nodules, especially for preoperative decision making , and Sonography guided FNAB has also improved its diagnostic accuracy remarkably recently . Most of the time, the purposeful or incidental finding of a thyroid nodule is first diagnosed by Ultrasonography (US) . Therefore, physicians usually decide if the nodule needs further evaluation based on these nodules’ sonographic features. However, most of these sonographic characteristics are shared between benign and malignant lesions . In this study, we tried to compare these sonographic features based on the ACR TIRADS model with final cytology reports of the thyroid nodules and evaluate how these features could make a physician suspicious of malignancy and additional procedures.
Despite an increased rate of thyroid nodule diagnosis following a growing variety of modalities, most of the nodules are benign . As in our study, 89.1% of the nodules were benign lesions, including benign follicular nodule, cystic fluid only, Colloid nodules, etc. However, different factors affect this prevalence, such as iodine deficiency, post-radiation therapy, and even patients’ level of health service accessibility in different societies [17, 18].
According to our experience, like some other studies [19, 20], the size of the nodules is not a good indicator of the risk of malignancy of thyroid nodules. However, some researches claim that there is a strong association between these two factors as the larger size of the nodules correlates with a higher malignancy rate with a threshold of 2.0 cm [21, 22]. Generally, the nodules’ size is not an important predictive indicator of thyroid malignancy unless accompanied by other malignant features .
In this study, surprisingly, we found no significant correlation between the TIRADS model and the risk of malignancy (p value = 0.45); this is in contrast with what Singaporewalla et al.  claimed in their research. They showed that there was an accuracy of 83% in predicting the risk of malignancy based on using TIRADS. However, the maximum correlation that we found was in TIRADS 2, with 16.9% of malignancy association. There are other studies by Horvath et al. , Park et al. , and Kwak et al.  that reported the leading association of TIRADS with the risk of malignancy 89.6%, 100%, and 87.5%, respectively. This may be due to our limited sample size, but notably, the TIRADS model is somehow operator dependent, as some studies suggest using this model by two radiologists at the same institution.
As mentioned above, all 147 patients underwent FNA under the guide of sonography to determine the accuracy of ACR-TIRADS classification and the correlation of histologic findings in accordance with sonographic features. In our experience, interestingly, TIRADS 2 had the most correlation with the risk of malignancy, which increases the uncertainty of using this scoring system as an indicator of thyroid nodules’ FNA necessity. We believe that this discrepancy may cause the misdiagnosis of patients who present with thyroid nodules with TIRADS 2 and will not be further assessed according to ACR-TIRADS.
Our study showed that there was a statistically significant (p = 0.013) correlation between malignancy and the location of thyroid nodules, and most of our cytologically malignant nodules were located in the right lobe. Although 67 out of all 77 nodules of the right lobe were benign, 10(13%) were malignant compared to 5 (7.7%) out of 65 nodules of the left thyroid lobe. Most studies claim that there is no relationship between the location of the thyroid nodules and malignancy and despite the absence of association, the isthmus and mid-lobar nodules were the most sites of the thyroid, which correlates with the risk of malignancy [26, 27].
In accordance with a retrospective observational cohort study conducted by Frates et al. , one of the sonographic characteristics which correlate with malignancy would be the existence of microcalcification. This finding is also in contrast with our study in which there was no association between the nature of calcification and the risk of malignancy (p value = 0.9). In another study by Rago et al. , only a combination of the presence of microcalcification plus the absence of halo sign had a significant relationship with the possibility of malignancy, which is associated with high specificity (93.0%) but low sensitivity (36.0%). Our research did not differentiate the subtypes of calcifications (such as micro, macro, coarse, and peripheral) and this may affect the results as some studies showed that although malignant thyroid nodules might correlate with microcalcifications, benign lesions are even associated with macro-calcification [30, 31].
Several studies have tried to determine if Fine Needle Capillary (FNC) sampling is superior to Fine Needle Aspiration due to a higher amount of cellular material, but they did not obtain statistically significant data [32, 33]. Although FNA sampling provides a more specific field and more diagnostic parameters than the FNC technique , our experience revealed that the samples accompanied by blood were significantly associated with more risk of malignancy (p value = 0.047).
In this study, we evaluated a relatively new variable to determine if the angle of the needle entry to thyroid nodules during FNA sampling affects the risk of malignancy. According to the results, there was no significant (p value = 0.47) correlation between the group of patients in whom the needle was induced in the angle of 75º and the other group who underwent this procedure with any other angle of needle entry.
Based on our experience in this research, hypoechogenicity is somehow associated with malignancy with a p-value of 0.058, which was statistically insignificant. However, Nabahati et al. revealed that there was a considerable positive correlation between malignancy and hypoechogenicity [odds ratio (OR) 3.577, 95% confidence interval (CI) 2.045–6.256] as their 29 nodules out of all 221 hypoechoic nodules were malignant (p value < 0.001). In our study, 26% of the thyroid nodules were hypoechogenic, and 20% were malignant. Overall, echogenicity is one of the criteria of ACR TI-RADS, and as in our study, the more hypoechogenic the thyroid nodule, the higher the risk of malignancy.