Which Ultrasound Characteristics Predict Lymphatic Spread of Papillary Thyroid Cancer?

Introduction: The 2015 American Thyroid Association guidelines recommend lymph node mapping US in patients with definitive cytological evidence of thyroid cancer. Suspicious lymph node features on imaging including enlarged size (>1 cm in any dimension), architectural distortion, loss of fatty hilum, and microcalcifications often prompt evaluation with fine needle aspiration. There is no universally agreed upon model for determining which ultrasound characteristics most strongly correlate with metastatic disease.

Methods: A retrospective review of patients with confirmed papillary thyroid cancer (PTC) undergoing lymph node mapping ultrasound from 2013 to 2019 was performed. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value were calculated for each individual ultrasound characteristic as well as for characteristic combinations.

Results: Data from 119 lymph nodes were included. Malignant lymph nodes were more likely to be enlarged (71% versus 61%, P < 0.001) and to have each individual suspicious feature. Loss of fatty hilum had the highest sensitivity (89%) but was not specific (19%) for metastatic disease. Architectural distortion was found to have the highest specificity (87%). A combination of the four features was found to have higher specificity (97%) and PPV (88%) than any individual feature or combination of two/three features.

Conclusions: A combination of four sonographic features correlates with metastatic PTC to lymph nodes and has the highest specificity and PPV for malignancy. A risk stratification model based on these features may lead to better classification of ultrasound findings in PTC patients with concern for nodal metastases.