Aim: This study reports the frequency of malignancy in thyroid nodules sonographically assessed as BTA U3 or greater (Indeterminate, Suspicious or Malignant) at a large tertiary institution, and assesses the synergistic performance of the BTA ultrasound (U) and cytology (Thy) grading in nodule stratification1.
Methods: Electronic record search at University Hospital Birmingham between 2014 and 2018 identified all thyroid fine needle aspiration cytology (FNAC), matched with corresponding ultrasounds scored as BTA U3 or greater. U2 nodules were excluded. Final nodule diagnosis was determined using a hierarchy of histopathology, FNAC, and clinical follow up.
Results: A total of 446 thyroid nodules with U3-5 and Thy1-5 scores were included in the analysis. The frequency of U classification was 69% (U3), 24% (U4) and 7% (U5) with corresponding malignancy rates of 13%, 30% and 67%. Frequency of Thy classification was 24% (Thy1), 31% (Thy1c/2/2c), 28% (Thy3a/3f), 10% (Thy4) and 7% (Thy5), with rates of malignancy 8%, 1%, 30%, 40% and 86%. The following observations are instructive: In U3 nodules, Thy1-2 result have low malignant risk (1.6%), but malignancy rates for other Thy scores (Thy3 (30%), Thy4 (33%) and Thy5 (50%)) are not significantly different. Therefore any U3Thy3+ nodule should be considered of similar malignant risk. In U4+ nodules, a Thy2 result has 8% malignancy risk; but all other Thy scores have a >20% risk of malignancy, including 32% malignancy risk for U4Thy3. Two nodules classified as Thy2 returned malignant histopathology - both were U4 on ultrasound. In Thy3 nodules, U classification does not further predict malignancy risk (U3=28% malignant, U4=33% malignant, p=0.72).
Discussion: Integrated assessment of thyroid nodules using ultrasound and cytology features result in greater diagnostic information than either modality alone. The BTA U/Thy system performs strongly to risk stratify nodules, with comparable data to published studies2.