Ultrasound of the Neonatal Spine¶
Definition¶
Spinal ultrasound is a non-invasive, radiation-free imaging modality used to evaluate the spinal cord, canal, and surrounding structures in neonates and young infants. It is possible because the posterior elements of the neonatal spine are incompletely ossified, providing acoustic windows for ultrasound transmission. This window closes by approximately 6 months of age as the posterior elements ossify.
Technique¶
Equipment¶
- Transducer: high-frequency linear array (7–15 MHz) provides excellent near-field resolution for the superficial neonatal spine
- Lower frequency (3–5 MHz) curved array may be needed for deeper structures in larger infants
Scanning Protocol¶
- Patient positioning: prone or lateral decubitus; a rolled towel under the abdomen helps flex the spine and widen the interspinous spaces
- Sagittal view: midline longitudinal view is the primary imaging plane — demonstrates the conus medullaris, cauda equina, filum terminale, and CSF pulsation
- Axial (transverse) view: provides cross-sectional evaluation of the cord, canal, and nerve roots
- Scanning should extend from the craniocervical junction to the sacrum — particular attention to the lumbosacral region
Key Structures to Identify¶
- Conus medullaris position (should terminate above L2–L3 in neonates)
- Filum terminale (should be thin, <2 mm)
- Cauda equina nerve roots (should be freely mobile within CSF)
- Ventriculus terminalis (a small CSF-filled cavity at the conus tip — normal variant)
- Vertebral bodies and posterior elements
Indications¶
Screening for Occult Spinal Dysraphism¶
Ultrasound is the first-line screening study in neonates with cutaneous markers suggesting underlying spinal anomalies:
- Sacral dimple — deep (>5 mm), large (>25 mm from anal verge), or atypical location
- Hairy patch (hypertrichosis) over the lumbosacral spine
- Subcutaneous lipoma or mass over the spine
- Skin appendage (tail-like structure)
- Dermal sinus tract
- Hemangioma overlying the spine
- Asymmetric gluteal cleft
Other Indications¶
- VACTERL association — vertebral anomalies, anorectal malformations, cardiac defects, tracheoesophageal fistula, renal anomalies, limb defects — spinal ultrasound is recommended as part of the evaluation
- Caudal regression syndrome
- Birth trauma — suspected spinal cord injury
- Follow-up of known abnormalities detected on prenatal imaging
Normal Findings¶
| Structure | Normal Appearance |
|---|---|
| Spinal cord | Echogenic (bright) central echo complex (central canal) with hypoechoic cord substance; tapers at conus |
| Conus medullaris | Terminates at or above L2–L3 level |
| Filum terminale | Thin, echogenic filament (<2 mm diameter) extending from conus to sacrum |
| Cauda equina | Thin, linear echogenic strands floating freely in CSF |
| CSF pulsation | Normal rhythmic motion of nerve roots and cord with cardiac cycle |
Abnormal Findings¶
| Finding | Significance |
|---|---|
| Low-lying conus (below L3) | Tethered cord; requires MRI for confirmation and surgical planning |
| Thick filum (>2 mm) | Tethered cord (fatty filum) |
| Intraspinal lipoma | Echogenic mass continuous with subcutaneous fat; associated with lipomyelomeningocele |
| Dermal sinus tract | Hypoechoic tract extending from skin surface toward the spinal canal |
| Absent nerve root motion | Suggests tethering or arachnoid adhesions |
| Diastematomyelia | Split cord with two hemicords — may show a bony or fibrous septum |
| Caudal regression | Absence of sacral segments; cord may be abruptly truncated |
Clinical Pearl
The acoustic window for spinal ultrasound closes by approximately 6 months of age as the posterior elements ossify. After this age, MRI is required for spinal cord evaluation. For this reason, if a cutaneous marker or clinical concern for spinal dysraphism is identified in a neonate, ultrasound should be performed promptly — delaying beyond 3–4 months risks losing the window. A normal ultrasound in a neonate with a simple, small midline sacral dimple (<5 mm, within 25 mm of the anus) is usually sufficient to exclude significant pathology.
Key Points¶
- Spinal ultrasound is the first-line screening study for occult spinal dysraphism in neonates
- It is possible because the neonatal posterior spinal elements are not yet ossified
- The acoustic window closes by ~6 months — study should be performed promptly
- Normal conus position is at or above L2–L3; a low conus suggests tethered cord
- Cutaneous markers (deep dimple, hairy patch, lipoma, dermal sinus) warrant screening
- Abnormal findings require MRI for confirmation and surgical planning
References¶
- Inarejos Clemente EJ, Navallas Irujo M, Navarro OM, Salas Flores B, Sousa Cacheiro P, Ladera E, et al. US of the spine in neonates and infants: a practical guide. RadioGraphics. 2023;43(6):e220136. doi:10.1148/rg.220136.
- Lowe LH, Johanek AJ, Moore CW. Sonography of the neonatal spine: part 1, normal anatomy, imaging pitfalls, and variations that may simulate disorders. AJR Am J Roentgenol. 2007;188(3):733–738. doi:10.2214/AJR.05.2159.
- Lowe LH, Johanek AJ, Moore CW. Sonography of the neonatal spine: part 2, spinal disorders. AJR Am J Roentgenol. 2007;188(3):739–744. doi:10.2214/AJR.05.2160.
- Rees MA, Squires JH, Coley BD, Hoehne B, Ho ML. Ultrasound of congenital spine anomalies. Pediatr Radiol. 2021;51(13):2442–2457. doi:10.1007/s00247-021-05178-6.
- Kucera JN, Coley I, O'Hara S, Kosnik EJ, Coley BD. The simple sacral dimple: diagnostic yield of ultrasound in neonates. Pediatr Radiol. 2015;45(2):211–216. doi:10.1007/s00247-014-3110-1.
- Wilson P, Hayes E, Barber A, Lohr J. Screening for spinal dysraphisms in newborns with sacral dimples. Clin Pediatr (Phila). 2016;55(11):1064–1070. doi:10.1177/0009922816664061.
- Nair N, Sreenivas M, Gupta AK, Kandasamy D, Jana M. Neonatal and infantile spinal sonography: a useful investigation often underutilized. Indian J Radiol Imaging. 2016;26(4):493–501. doi:10.4103/0971-3026.195788.
- Asil K, Yaldiz M. Conus medullaris levels on ultrasonography in term newborns: normal levels and dermatological findings. J Korean Neurosurg Soc. 2018;61(6):731–736. doi:10.3340/jkns.2016.1212.001.