In this article, the authors will present an overview of the use of ultrasound of the spinal canal in infants and young children. Ultrasound of the spinal cord offers several advantages over other imaging techniques in that it may detect many abnormalities, requires no infant sedation, is performed quickly, and provides exquisite detail.
Dr. Gerscovich is Professor of Radiology and Associate
Director of Abdominal Imaging and Ultrasound, and Dr. McGahan
is Professor of Radiology and Director of Abdominal Imaging and
Ultrasound at University of California Davis Medical Center,
Sacramento, CA. Dr. McGahan is also a member of the editorial
board of this journal.
The use of ultrasound for examination of the spinal canal in
infants and children is not new. It was first described by several
authors in publications in 1983.
With the advent of widespread use of magnetic resonance imaging
(MRI), sonography of the spine of the young child has often been
forgotten or may be used as a secondary modality. Magnetic
resonance imaging has become the gold standard for examination of
the spine in the adult and pediatric population for a number of
However, ultrasound has been recommended as a valuable diagnostic
tool in the evaluation of the lumbar spine in infants and is
"recommended as the primary imaging modality in those patients."
Ultrasound examination of the lumbar spine in infants or young
children has several advantages. First, recent technical
innovations in sonographic imaging, especially the improved
nearfield resolution, allow exquisite anatomical detail of the
spinal canal. Furthermore, ultrasound uses no radiation, requires
no infant sedation when examining the spine, is performed rather
quickly, and is relatively inexpensive compared with MRI. In this
article, we will present an overview of the use of ultrasound of
the spinal canal in infants and young children.
Ultrasound is most often utilized in the newborn to check for
tethering of the spinal cord and associated abnormalities. Infants
with various midline back abnormalities, including hemangiomas,
lipomas, a hairy patch, or a dimple may be screened with
Other abnormalities such as bony anomalies of the lumbosacral spine
or neurogenic bladder may be associated with a tethered cord.
Ultrasound may also be useful in examining cases of spinal
dysraphism including myelomeningocele and may be used in the
follow-up of these cases to check for cord tethering after repair.
The technique for examination of the spinal cord in neonates is
quite simple. A high-resolution linear array (7.5 MHz or greater)
probe is used. Patients are brought into a quiet room and are often
fed prior to the examination. A small towel may be placed under the
abdomen of a young child to help separate the posterior neural
elements for better sonographic visualization of the spinal canal
(figure 1). In newborns, the spinal canal may be examined in the
midline longitudinal plane or the transverse plane. In older
children, either slight angulation or scanning slightly lateral is
needed for scanning in the longitudinal plane, to avoid shadowing
from the ossification centers of the posterior spinous
The cord itself is hypoechoic. It exhibits a central echogenic
line, which extends for the length of the cord and is visualized
easily on both longitudinal and transverse imaging (figure 2).
Originally, this central echo complex was thought to represent the
central canal of the cord. However, work by Nelson et al
showed that this central echogenicity is produced by interfaces
between the myelinated ventral white commissures and the central
end of the anterior median fissure. The normal cord smoothly tapers
distally at the conus medullaris and is surrounded at this point by
the fairly echogenic nerve roots of the cauda equina. One of the
important elements in examination of the newborn spinal canal is
determination of the caudal extent of the tip of the spinal cord.
Surprisingly, studies of the fetus in the third trimester and young
children have fairly similar results. In general, in the neonate or
young adult, the conus level should basically be at L2 or higher.
Rarely, it may extend to the L2-3 or L3 level.
This level should remain fairly constant throughout childhood.
Thus, determination of the conus level is of the utmost importance.
Extension of the spinal cord below the L2-3 region is usually
associated with tethering of the same.
The location of the distal cord can easily be determined with
ultrasound by recognizing that there is usually a normal lordotic
transition of the lumbar vertebral bodies to the sacral vertebral
bodies. This lumbosacral transition demarcates the L5-S1 interface.
It may be recognized on longitudinal scans by two intersecting
lines. These lines should be drawn from a line tangent to the
lumbar vertebral bodies that intersect the line drawn tangent to
the sacral vertebral bodies.
In the newborn, usually S5 is the lowest ossified vertebral body
that can be recognized. Thus, counting upwards from S5 will be
another method to cross-check the exact vertebral level (figure 3).
Further confirmation of the exact level of the conus medullaris can
be obtained in transverse imaging. In transverse imaging, the top
of the iliac crest is usually identified when scanning through the
L5 vertebral body. When scanning laterally to the L2 vertebral body
the tip of the 12th rib usually can be identified.
If there is any doubt of the location the conus medullaris by
ultrasound, a metallic marker can be placed over the conus and this
can be verified by a plain radiograph. This is required only
Other anatomical detail may be visualized with ultrasound,
including the dentate ligaments in the thoracic cord, extending
laterally from the cord (figure 4), and the echogenic interfaces of
the dorsal and ventral cord.
Color Doppler ultrasound may also demonstrate the anterior spinal
artery and the epidural veins surrounding the cord (figure 5).
Usually, the spinal cord and cauda equina oscillate synchronously
with cardiac motion. This oscillation is an important observation,
as it may be absent with tethering of the spinal cord (figure 6).
In the newborn, the whole spinal canal and cord can be visualized
up to the foramen magnum (figure 7).
Tethered cord--As previously described, tethering of the cord is
a general term to describe low ending of the spinal cord usually
due to a variety of etiologies. The ultrasound finding of a
tethered cord includes the distal cord lying below the L3 level
(figure 8), the cord often being eccentrically displaced dorsally,
and cord oscillations being decreased or absent.
Spinal tethering may be associated with a number of abnormalities
such as dermal sinus, lipoma, diastematomyelia, thick filum
terminale, and bony abnormalities. Ultrasound may be helpful to
identify these abnormalities. For instance, a dermal sinus can be
observed sonographically as a hypoechoic band extending from the
spinal canal to the cutaneous tissues of the back. Lipomas are
recognized as well-demarcated echogenic masses in the spinal canal
or subcutaneous soft tissues (figure 9). These masses may be
associated with a lipomyelomeningocele with the subarachnoid space
and nerve rootlets bulging into the subcutaneous tissues of the
back, under an intact skin.
Diastematomyelia--Diastematomyelia is a split of the spinal cord
in two halves (figure 10). Usually there is a bony spicule or
fibrous band in the area of the spina bifida. This defect may or
may not be covered by intact skin. The two portions of the cord may
be best demonstrated sonographically in transverse section.
There may be associated spina bifida in these patients. There also
may be concurrent hydromyelia.
The ultrasound appearance of the split spinal cord is pathognomonic
in these cases.
Open neural tube defects--Prenatally, sonography is important
for recognizing the findings of the Chiari Type II malformation.
The most commonly sonographically recognizable intracranial
abnormalities are the "banana" sign or the "lemon-shaped" head.
In detection of open neural tube defects, Budorick et al
have emphasized that the cranial abnormalities associated with the
Chiari Type II malformation are much more obvious than the spinal
abnormalities. However, postnatally ultrasound is excellent for
examining open neural tube defects occurring in the lumbosacral
Spina bifida is the general term to describe open forms of
spinal dysraphism that result from failure of the posterior neural
pores to close. These defects can be from fairly simple to complex.
Meningoceles are cystic lesions that result from protrusion of the
meninges through the spinal defect (figure 11). Myelomeningoceles
also contain abnormal central nervous system tissue in the defect.
These lesions are usually large and covered by a membrane of
meningeal origin and malformed spinal cord substance.
Ultrasound may be very useful in the newborn to identify the level
of the distal cord as well as the size of the defect and the neural
elements that are contained within the defect.
Postoperative repair--Ultrasound may be helpful to identify
abnormalities that can occur after surgical repair of
myelomeningoceles. The cord may retether in these abnormalities due
to adhesions. Sonographically, this may be observed as the cord
being tightly adhered to the posterior wall of the distal spinal
canal (figure 12) with decreased oscillations. Other persistent
abnormalities can be observed in patients after surgical repair,
including epidermoid and dermoid tumors resulting from epithelial
tissue that was not removed at the initial operation, or increasing
hydromyelia. A thick filum terminale or diastematomyelia can be
seen after cord-release surgery. Ultrasound may be helpful to
recognize these abnormalities.
Ultrasound has a number of uses for evaluation of the spinal
cord in the infant and young child. Ultrasound of the spinal cord
is fairly quick and easy to perform and may be useful in detecting
many abnormalities. It has a number of advantages over other
imaging techniques as it requires no infant sedation, is performed
quickly, and provides exquisite detail. AR
Special thanks to Deborah Hoang for her assistance in the
preparation of the manuscript.