Related Experiment Video
Updated: Oct 3, 2026
Clinical Efficacy of an Innovative Multidimensional Traction Therapy in Moderate Adolescent Idiopathic Scoliosis
Published on: February 10, 2026
Re-evaluating prone-position MRI markers in occult tethered cord syndrome: a prospective observational study
Bilal Younes1, Christian Riedel2, Fares Komboz3
1Department of Neurosurgery, University Medical Center Göttingen, Robert-Koch-Straße 40, Göttingen, 37075, Germany. bilal85sy@gmail.com.
Objective:
Occult Tethered Cord Syndrome (OTCS) is defined as a clinical syndrome of cord tension with symptomatology similar to Tethered Cord Syndrome (TCS) but lacking typical imaging features, with the conus medullaris (CM) terminating at a normal level above the second lumbar vertebral body. A posteriorly displaced filum terminale (FT) on prone MRI, termed the "sunrise sign," has been proposed as a diagnostic marker for OTCS. This study aimed to characterize the position of the CM and FT and to determine the prevalence of the sunrise sign in asymptomatic adults.
Methods:
In this prospective observational study, 20 healthy volunteers underwent prone lumbar MRI at 3.0 Tesla. High-resolution axial and sagittal T2-weighted sequences were acquired to evaluate the CM, FT, CE, and dural sac (DS). Quantitative measurement included the anteroposterior diameter of the subarachnoid space, distances from the posterior dura to the FT and to the dorsal/ventral nerve roots of the cauda equina (CE), and calculated location ratios (TF, DN, VN). The sunrise sign was defined as dorsal FT displacement > 4 mm relative to the most dorsal nerve root. Interobserver reliability and group comparisons between sunrise and non-sunrise participants were performed.
Results:
The sunrise sign was observed in 12 of 20 volunteers (60%; 95% CI 39%-78%). The CM terminated at L1 in 85% and at L2 in 15%. The FT contacted the dorsal dura most frequently at L4 (65%). In the sunrise group, the distance between FT and CE was significantly greater at levels L2-3 through L4-5 (p < 0.0001), with significantly lower TF ratios at L2-3 and L3 (p = 0.011 and p = 0.0016, respectively) and higher DN ratios at L3-4, L4, and L4-5 (p = 0.004, p = 0.03, and p = 0.004, respectively) compared to the non-sunrise group. No significant differences were observed in VN ratios, indicating comparable spinal canal dimensions between groups.
Conclusion:
The "sunrise sign" on prone MRI is a common anatomical variant, present in nearly half of asymptomatic individuals, thereby challenging the specificity of this particular FT-CE configuration. Further comparative studies are warranted to more precisely determine the sensitivity and specificity of this imaging finding.
