The Role of Power Doppler Ultrasonography in Caudal Epidural Injection

Background and Objectives: Although the ultrasound-guided technique is used in caudal epidural injections, severe complications can happen if ultrasound cannot identify the occurrence of intravascular injection. To determine intraepidural and intravascular injection during caudal epidural injections, we used power Doppler ultrasonography (PDU) when injecting medications into the epidural space. Materials and Methods: This is a retrospective study that enrolled a total of 277 patients with refractory low back pain or degenerative disc from January 2019 to December 2019. The injectate flow of caudal epidural injections was examined with the assistance of PDU and confirmed by fluoroscopy. Four flow patterns were identified by PDU in our study: the "Earthworm sign," the "Patch sign," the "Tubular sign" and the "Absent flow sign." The accuracy of PDU in identifying intraepidural and intravascular injections was determined by fluoroscopy images recorded during each injection. Results: We evaluated 277 patients (mean age, 68.6 ± 13.2 years; 106 men). The "Patch sign" showed a sensitivity of 88.76% and a specificity of 80% in predicting epidural injection without intravascular injection. The "Earthworm sign" demonstrated a sensitivity of 70% and a specificity of 100% in detecting intravascular injection. The "Tubular sign" showed a specificity of 100% and a sensitivity of 9.4% in predicting successful epidural injection. The absence of a flow signal showed a sensitivity of 1.87% and a specificity of 90% in predicting successful epidural injection. Conclusions: Ultrasound-guided caudal epidural injection can accurately determine intraepidural and intravascular injections with the assistance of PDU and is thus a good alternative technique to fluoroscopy-guided caudal epidural injection.