Diagnostic accuracy of ultrasonography to distinguish thyroglossal duct cysts from dermoid cysts in children with a midline neck swelling

Introduction: Midline neck swellings are very common in children and mostly caused by thyroglossal duct cysts (TGDCs) or dermoid cysts (DCs). Since DCs can undergo simple excision, whilst TGDCs demand more thorough resection via Sistrunk procedure, it is important to differentiate between both pre-operatively. Previous studies have suggested an ultrasound-score (SIST) based on presence of septae, wall irregularity and solid components could do so. This study aims to evaluate the diagnostic accuracy of this score. Methods: All patients (≤18 years) undergoing surgery between 2006 and 2018 for a midline neck mass at our tertiary centre with a histopathological diagnosis of TGDC or DC were retrospectively included. The pre-operative ultrasound was evaluated by an experienced radiologist and the SIST as well as location, tract, echogenicity, margin and multilocularity were scored. Results: We included 97 children, of whom 67 (69 %) with TGDCs. The SIST showed a sensitivity of 37 %, specificity of 97 %, a positive predictive value of 96 % and a negative predictive value of 35 % for the SIST-score in detecting TGDCs, which resulted in an AUC of 0.67. In addition, internal echogenicity (P < 0.01) and margin definition (P < 0.01) were significantly associated to TGDC diagnosis whilst location and multilocularity were deemed insignificant following Bonferroni correction. Conclusion: We conclude that the SIST-score seems very capable to rule in TGDC. However, the SIST-score is far from making a clear distinction between DC and TGDCs preoperatively. The addition of other ultrasound variables, such as margin definition and echogenicity, might increase the diagnostic accuracy and demands further research.