Ultrasound is the most commonly used imaging technique in the evaluation of thyroid nodules so it is essential to establish a lexicon that provides a structured method for evaluation of thyroid nodules whether the benign or the malignant group [6]. ACR TI-RADS is used as a guideline in stratification of thyroid nodules on the basis of their risk of malignancy [8]. The ACR TI-RADS guidelines were developed to facilitate a standard approach to assess nodular features and to decrease the variation seen in reporting of thyroid nodules in current practice among interpreters with varying levels of sonographic expertise and also to develop guidelines for further management. Five items were assigned (composition, echogenicity, shape, margin, and presence of echogenic foci) and the total points are summed to determine the overall TI-RADS level that ranges from one to five according to the risk of malignancy. For each level, a specific size cut off for FNA is recommended [1].
Our study included 40 thyroid nodules, and ultrasonographic appearance of the thyroid nodules was interpreted using a ACR TI-RADS template to determine whether they belong to the benign or the malignant group. Allocation of points for different sonographic findings mirrors the likelihood that those finding are associated with malignancy; these data were confirmed finally by scintigraphy and histopathological reports after FNA or surgical excision.
Malignancy is uncommon with predominantly cystic nodules [8]. Also, Ahn et al. [9] found that thyroid cancers are more likely to be solid or nearly entirely solid. In our study, all nodules with cystic changes (predominantly cystic) were benign, and there was a highly significant increase in the incidence of solid nodules in the malignant group than in the benign group (P value ˂ 0.001).
Regarding echogenicity, there were many studies that showed that the risk of malignancy is inversely proportional to nodule echogenicity; the more echogenicity, the less possibility of malignancy. Papillary and medullary thyroid cancer appears hypoechoic due to increased cellular impaction [10]. The exception to this theory is the follicular dominant pathology which is composed of small microfollicles and tends to appear hyperechoic [5, 11, 12]. In our study, there was a highly significant increase in anechoic and hyperechoic nodules in the benign group (P value = 0.025 and 0.036 respectively), while there was high increased incidence of very hypoechoic nodules in the malignant group (P value = 0.001) and there was no significant difference between the benign and the malignant groups regarding isoechoic and hypoechoic thyroid nodules; this could be related to the histological subtypes of neoplasms included in the study population rather than true frequency.
Middleton et al. [8] found that 12.9% of nodules with smooth margins and 44. 7% of nodules with a lobulated or irregular border were malignant. Irregular and lobulated margins are suspicious for thyroid malignancy [13]. We had comparable results in our study; we found that 11.1% of the malignant group nodules had smooth margins and 66.7% of the malignant group nodules had lobulated or irregular margins. It is important to assess extrathyroidal extension when evaluating thyroid malignancy. In our study, extrathyroidal extension was detected in two patients.
Regarding the shape, thyroid cancer is associated with nodules with a ratio of anteroposterior to transverse diameter greater than one in the transverse view. Specificity ranges from 82 to 93%; this means that it is a less suspicious nodule [9, 14]. In agreement with these previous studies, we found that there was a statistically high significant increase in the incidence of taller than wider nodules in the malignant group than in the benign group with P value 0.001
Middleton et al. [8] found that the risk of malignancy associated with peripheral calcifications, and punctate echogenic foci in solid nodules was 20.2% and 35% respectively; we had comparable results to those reported as we found that 11.1% of the malignant nodules had peripheral calcifications and 66.7% of the malignant nodules had punctate echogenic foci. Our study also agreed with Reading et al. [15] that macrocalcifications were found within both benign and malignant nodules yet more in the benign nodules.
Regarding the diagnostic accuracy of TI-RADS scoring system studied by Tressler et al. [1], they found an increased risk of malignancy in thyroid nodules starting from TR3 (5%) to TR4 and TR5 (20%). Another study done by Middleton et al. [8] stated that the risk of malignancy is 4.8%, 9.1%, and 35%, for TR 3, TR4, and TR5 respectively.
In our study, we found that the best cut off point to detect malignant cases was 5 (corresponding to TI-RADS level 4) with a sensitivity of 88.89%, specificity of 96.77%, PPV of 88.9%, and NPV of 69.8%. A statistically significant trend of an increasing risk of malignancy was noted as the total points increased (P value < 0.001) and as the final TI-RADS level increased from TR1 to TR5 (P value < 0.001) (Table 6).