To establish a preoperative ultrasound prediction model by binary Logistic regression analysis to explore its predictive ability for central lymph node metastasis risk of papillary thyroid microcarcinoma.

From January 2014 to July 2016, 352 patients diagnosed with PTMC by postoperative pathology at Zhejiang Provincial People's Hospital were selected, with a total of 413 thyroid lobes and ipsilateral central lymph nodes. The preoperative ultrasound images were retrospectively analyzed, and the variables affecting the pathological results of central lymph node metastasis were analyzed by forward Logistic regression to establish an ultrasonic prediction model. After the model was established, 186 consecutive PTMC patients were included from January 2017 to October 2017 as a model validation group, with a total of 229 glandular lobes and ipsilateral central lymph nodes. The model was used to predict the risk of central lymph node metastasis in the validation group, and the result was compared with postoperative pathology. The receiver operating characteristic (ROC) curve was plotted to evaluate the prediction effect of the model.

Using preoperative ultrasonographic features as independent variables and central lymph node metastasis (with or without) as dependent variables, Logistic regression analysis showed that the variables that finally entered the model were X₁ (maximum diameter of cancer lesion: 5~10 mm), X₂ (multiple cancer lesions), X₆ (micro-calcification area ≥ 1/2 of the cancer lesion area), and X₉ (extra-thyroid invasion). The model was: Y=-2.52+ 1.36X₁+ 0.63X₂+ 2.06X₆+ 2.19X₉; P=e^Z/1+ e^Z (P represents the probability of central lymph node metastasis, and e is the natural constant 2.72). When applying the model to the verification group, the accuracy, sensitivity, missed diagnosis rate, specificity, misdiagnosis rate, positive likelihood ratio, and negative likelihood ratio were 89.08%, 91.36%, 8.64%, 87.84%, 12.16%, 7.513, and 0.098, respectively. The largest area under the ROC curve was 0.931.

The ultrasonic prediction model developed in this study has a good prediction ability for central lymph node metastasis in PTMC patients, which is, to a certain extent, helpful to improve the preoperative diagnosis rate and select clinical treatment scheme reasonably.