Contrast-enhanced ultrasound: a valuable modality for extracapsular extension assessment in papillary thyroid cancer

To evaluate the diagnostic accuracy of preoperative contrast-enhanced ultrasound (CEUS) to detect extracapsular extension (ECE) and identify the relationship between ECE and nodule enhancement patterns in patients with papillary thyroid cancer (PTC). Patients with suspected thyroid cancer underwent ultrasound (US) and CEUS examinations. The US and CEUS features of the PTC nodules and thyroid capsule were recorded and classified individually. The accuracy of US and CEUS in detecting ECE was compared individually, and its relationship with various tumour enhancement patterns was analysed. The presence or absence of ECE and cervical lymph node metastasis (LNM) was confirmed pathologically. The final dataset included 119 patients with 124 PTC nodules. Seventy-two (60.5%) of these patients with PTC had no ECE (including 38 patients with single capsule invasion), while the remaining 52 had ECE. A significant difference was found in nodules with non-capsule invasion, single capsule invasion, and ECE between the cervical LNM and non-LNM groups (p < 0.01). Receiver operating characteristic curve analysis demonstrated that area under the curve (AUC) of ECE for cervical LNM was higher than that of capsule invasion (71.9% vs. 49.6%). Moreover, the CEUS images acquired to detect ECE showed higher AUC values than those of US images (79.4% vs. 65.8%) (p = 0.02). Among the PTC nodules with differential enhancement, hyper-enhanced nodules had the highest incidence of capsule invasion (41.9%), while hypo-enhanced ones had a higher incidence of ECE (47.4%). Compared with conventional US, CEUS is a more valuable and non-invasive imaging modality to detect ECE. • Single capsular invasion was a poor predictor of cervical lymph node metastasis, while extracapsular extension assessments were clinically significant for predicting cervical lymph node metastasis. • CEUS is better than conventional US in detecting extracapsular extension in papillary thyroid carcinoma (AUC: 79.4% vs. 65.8%) (p = 0.02). • Among the thyroid papillary carcinoma nodules with differential enhancement, hyper-enhanced nodules had the highest incidence of single capsule invasion (41.9%), while hypo-enhanced ones had a higher incidence of ECE (47.4%).