Shorter distance between the nodule and capsule has greater risk of cervical lymph node metastasis in papillary thyroid carcinoma

The purpose of this study was to assess the relationship between different sonographic features of papillary thyroid carcinoma (PTC) on high-frequency ultrasound and cervical lymph node metastasis (CLNM).

We enrolled 548 patients who underwent initial surgery for PTC between May 2011 and December 2012 in our hospital at diagnosis. The sonographic features of 513 PTC nodules in 513 eligible patients, who had single PTC nodules in their thyroid glands, were retrospectively investigated. All patients with a suspect malignant nodule (d<0.5cm) among multiple nodules were initially diagnosed by fine-needle aspiration biopsy (FNAB) to ascertain if the suspect nodule was PTC. The final diagnosis of all the thyroid nodules and existence of CLNM were based on postoperative pathology. Patients were divided into two groups: a positive group with CLNM (224 nodules) and a negative group without CLNM (289 nodules). The following factors were investigated: gender, age, echogenicity, echotexture, size, shape, location, margin, contour, calcification morphology, distance between the nodule and pre- or post-border of the thyroid capsule, vascularity and the differences between the two groups.

Correlation analysis showed that shorter distances between the nodule and pre- or post- border of thyroid capsule resulted in greater risk of CLNM (Spearman correlation coefficient=-0.22, p<0.0001). The significant factors in multivariate analysis were age<45yrs, larger size (d>1cm), "wider than tall" shape, extrathyroid extension and mixed flow (internal and peripheral) (p<0.05, OR=0.406, 2.093, 0.461, 1.610, 1.322).

Significant sonographic features of PTC nodules in preoperative high-frequency ultrasound are crucial for predicting CLNM.