Introduction: Tethered cord syndrome can result from a variety of conditions including abnormalities of the filum terminale or surrounding structures that prevent the normal ascent of the conus medullaris. Magnetic resonance imaging (MRI) and ultrasound imaging are used as screening and diagnostic tools; however, they have their individual strengths and weaknesses, which create controversy regarding the preferred initial imaging modality.
Methods: The authors performed a retrospective review of the radiographic images 219 infants born with concerns for low-lying conus medullaris. A subset of 44 patients had both lumbar ultrasonography and MRI performed within 4 weeks of each other. Numerical values were assigned to the vertebral level of the conus medullaris: L1=1, L2=2, L3=3, L4=4 L5=5, L6=6. If the conus was located opposite the disk space at the junction of two vertebral bodies, the numerical value was averaged.
Results: Among the 219 patients included in our study, the average level of the conus medullaris based on the ultrasound findings was 3.1 (range L1 to L5, SD=±0.9) and 2.9 (range L1 to L5.5, SD=±1.0) based on MRI. The vertebral level on ultrasonography correlated with that on MRI in 17 patients (39%), differed by 0.5 level in 16 patients (36%), differed by 1 full level in 10 patients (23%), and by 1.5 levels in one patient (3%). There was no statistically significant difference in conus medullaris levels based on spinal ultrasound imaging findings compared to those on MRI (p=0.388). When only patients with a conus medullaris level at or below L3 were considered (33 patients), there was no statistically significant difference in the level of the conus medullaris based on the spinal ultrasound compared to that based on the MRI (p=0.236).
Conclusions: Although not always accurate, spinal sonography is generally an adequate modality for first-line screening for tethered cord syndrome in patients with suspected low-lying spinal cord.
Patient Care: Spinal ultrasonography is more affordable and more comfortable for pediatric patients being evaluated for low-lying conus medullaris.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Compare the relative accuracy of spinal MRI and ultrasound to evaluate the level of the conus medullaris
References: 1. Yamada, S., D.J. Won, and S.M. Yamada, Pathophysiology of tethered cord syndrome: correlation with symptomatology. Neurosurg Focus, 2004. 16(2): p. E6.
2. Deeg, K.H., H.M. Lode, and I. Gassner, Spinal sonography in newborns and infants - part II: spinal dysraphism and tethered cord. Ultraschall Med, 2008. 29(1): p. 77-88.
3. Nakanishi, K., et al., Use of prone position magnetic resonance imaging for detecting the terminal filum in patients with occult tethered cord syndrome. J Neurosurg Spine, 2013. 18(1): p. 76-84.