Reliable sonographic features for nodal thyroglobulin to diagnose recurrent lymph node metastasis from papillary thyroid carcinoma

Objectives: Ultrasound-guided aspiration cytology (US-FNAC) was previously used to diagnose lymph node metastasis of papillary thyroid carcinoma (PTC). Combined US-FNAC with nodal thyroglobulin (LN-FNA-Tg) significantly improved the diagnostic rate. However, diagnostic accuracy depends on proper node selection. Therefore, it is crucial to choose the nodes with reliable sonographic features to guide clinician for confirmation.

Design and setting: Retrospective cohort study was carried out in one medical centre from 2011 to 2014.

Participants: A total of 148 patients with PTC, being treated by total thyroidectomy and radioiodine, were assessed for potential nodal metastases by ultrasound.

Main outcome measures: Lymph nodes with cystic content, peripheral hypervascularity, calcification, hyperechoic content, the absence of hilum and Solbiati index < 2 indicated risk of malignancy. US-FNAC and LN-FNA-Tg were both performed. Positive nodal metastasis was further confirmed by dissection. Risk impact of these sonographic features on LN-FNA-Tg to diagnose nodal metastasis was tested by logistic regression analysis based on the significance in both univariate and multivariate models.

Results: Overall, 49 lymph nodes were documented as recurrent nodal metastasis. LN-FNA-Tg greater than serum thyroglobulin and higher than 1 ng/mL achieved 100% of diagnostic rate for recurrent nodal metastasis. The malignant sonographic features that significantly cohered with positive LN-FNA-Tg were cystic and hyperechoic content and lack hilum, in sequence.

Conclusions: LN-FNA-Tg is an excellent tool to quantitatively diagnose nodal metastasis. To achieve ideal diagnosis, the most reliable sonographic features were cystic content, hyperechoic content and the absence of hilum in lymph nodes, but not calcification or Solbiati index < 2.