Ultrasonographic features of the normal filum terminale

PURPOSE: The filum terminale (FT) is a fibrous band that connects the conus medullaris to the posterior body of the coccyx. Considering the advances of ultrasonography (US) technology and improvements in the resolution of US images, we aimed to re-establish the US features of the normal FT in infants younger than 6 months of age. METHODS: We retrospectively reviewed 30 spinal US scans, stored as video clips. The internal structure of the FT and the marginal echogenicity of the FT were assessed, and transverse and longitudinal US were compared. RESULTS: On US, a central echogenic line was defined in 18 (60%) normal FTs; however, there was no visible internal structure in 12 cases (40%). The marginal echogenicity of the FT was hyperechoic in eight cases (27%) in comparison with the cauda equina and was isoechoic in 22 cases (73%). In differentiating the normal FT from the surrounding nerve roots, transverse US was superior in 18 cases (60%), while longitudinal US was superior in two cases (7%). CONCLUSION: On US, the central canal of the FT was defined in 60% of normal FTs. Hyperechoic marginal echogenicity and the use of transverse US were helpful in distinguishing the normal FT from the nerve roots of the cauda equina.