Preoperative hydrodissection for predicting extrathyroidal extension in thyroid tumors

Background: We aimed to evaluate diagnostic performance of preoperative hydrodissection and grey-scale imaging (US) in predicting extra-thyroidal extension (ETE) of subcapsular thyroid lesions. Methods: The retrospective study evaluated hydrodissection between September 2023 and March 2025 for subcapsular thyroid nodules. Biopsy specimen with atypia of undetermined significance and thyroid tumors without surgery were excluded. For US, ETE was determined based on following features: capsule disruption, bulging contour, and perithyroidal infiltrations. For hydrodissection, ETE was determined positive if resistance was encountered. Diagnostic performance comparing US and hydrodissection in predicting ETE was performed for K-TIRADS 5 nodules and thyroid tumors. Results: A total of 40 nodules per 33 patients (age: 50.2 ± 12.7; female: 28/33, 84.9%) were included. Out of 40 nodules, 18 nodules were tumors, of which 15 nodules (83.3%) were malignant. Four malignant nodules demonstrated ETE. For K-TIRADS 5 nodules (n = 28), hydrodissection demonstrated better diagnostic performance in terms of specificity (0.96 vs. 0.63, p = 0.008), accuracy (0.93 vs. 0.61, p = 0.004), and AUC (0.854 vs. 0.563, p = 0.013). For thyroid tumors (n = 18), hydrodissection demonstrated higher accuracy (0.89 vs. 0.56, p = 0.031) and higher AUC (0.839 vs. 0.536, p = 0.016). Conclusion: Hydrodissection demonstrated better specificity, better accuracy, and higher AUC in predicting ETE than US.