"Onion Skin-liked Sign" in Thyroid Ultrasonography: A Characteristic Feature of Benign Thyroid Nodules

Using Ultrasonography to Evaluate the Relationship between Capsular Invasion or Extracapsular Extension and Lymph Node Metastasis in Papillary Thyroid Carcinomas

Background:

Previous studies have demonstrated that ultrasonography is the recommended imaging modality for preoperative staging of papillary thyroid carcinomas (PTCs). However, only a few studies have kept watch on preoperative evaluation of capsular invasion (CI) or extracapsular extension (ECE) and cervical lymph node metastasis using preoperative ultrasonography. This study aimed to investigate the relationship between the CI or ECE and the cervical lymph node metastasis in PTCs using preoperative ultrasonography and postoperative pathology in Chinese patients.

Methods:

The data of preoperative ultrasonography and postoperative pathology of 166 patients who had a definitive diagnosis of PTCs from October 2011 to July 2014 at Xuanwu Hospital, Beijing were collected and reviewed. Preoperative ultrasonic parameters of thyroid nodules were compared with those of postoperative pathological diagnoses. All the patients were divided into bilateral PTCs group (n = 42, 78 nodules) and unilateral PTCs group (n = 124, 124 nodules), and the data of the nodule sizes, CI or ECE, and cervical lymph node metastasis by preoperative ultrasonography were compared between two groups.

Results:

A total of 202 nodules of 166 patients which were confirmed by preoperative ultrasonography and postoperative pathology were analyzed. Hypoechogenicity (n = 201, 99.5%) and irregular margins (n = 167, 82.7%) were the main ultrasonic characteristics of PTCs. A significant moderate agreement between preoperative ultrasonic examination and postoperative pathology for CI or ECE (κ = 0.622, P < 0.001) was observed. The diagnostic sensitivity was 92.0%, and specificity was 71.1%. In bilateral PTCs group, 81.0% had CI or ECE, and 61.9% had cervical lymph node metastasis. In unilateral PTCs group, 76.6% had CI or ECE, and 58.1% had cervical lymph node metastasis. There were no significant differences in the incidence of CI or ECE and cervical lymph node metastasis between two groups (all P > 0.05).

Conclusions:

Ultrasonography was proved to be a valuable method for preoperative diagnosis of PTCs. Hypoechogenicity and irregular margins were strongly associated with PTCs. CI or ECE in unilateral PTCs strongly implied the cervical lymph node metastasis. Therefore, the cervical lymph nodes should be carefully examined by ultrasonography in patients with PTCs.