Diagnostic ultrasound ( PDFDrive )

CHAPTER 49 The Pediatric Spinal Canal 1677
A
B
FIG. 49.6 Normal Vertebral Sonographic Anatomy. (A) Sagittal view of the distal lumbar spine shows ine deinition of vertebral body
anatomy. The cartilaginous tips of the posterior spinous processes are visible (arrows), as well as the posterior margin of the cartilaginous portion
of the L3 vertebral body (curved arrow). (B) More distal sagittal view shows the cartilaginous posterior elements of the midsacral spine (arrows).
FIG. 49.7 Fluid Within Central Canal (Ventriculus Terminalis). Sagittal
view of the lumbar spine. This is a common, normal variant (arrow)
observed in many infants.
FIG. 49.8 Normal Filum Terminale. This can be clearly distinguished
from the nerve roots and should be less than 2 mm in diameter (arrows).
The external edges of the ilum are relatively bright compared with the
central portion of the ilum. See also Video 49.2.
Some infants have more prominent epidural fat, which also
should be considered a normal variant unless other signs suggest
an abnormal fatty mass (Fig. 49.10). Color Doppler ultrasound
can help localize the epidural venous plexus, anterior spinal
arteries, and paired posterior spinal arteries. Malposition,
compression, or distention of these vessels may help to distinguish
an abnormal mass within the vertebral canal from normal nerve
rootlets or epidural fat.
Determination of the position of the tip of the conus medullaris
is the most common indication for spinal ultrasound and
should always be included in a neonatal spine sonographic
examination. Approaches, all of which presume normal anatomy,
include (1) inding the lowest rib (presumably the 12th rib) on
lateral parasagittal scanning, following medially to the vertebral
body and counting down from this level; (2) deining the longitudinal
lumbosacral junction where S1 is the irst vertebral
body that tilts posteriorly (similar to a lateral spine radiograph)
and using that as a reference 12 ; (3) deining the distal end of the
thecal sac which is usually at S2 12 ; and (4) counting upward from
the last ossiied “sacral” vertebral body. he fourth approach can
be inaccurate because of the great variability in the ossiication
of the coccygeal vertebral bodies. 23 In general, ossiied coccygeal
vertebral bodies have a rounded central nucleus, whereas sacral
ossiication centers take on a more squared contour. If at least
two methods are applied and the vertebral assignment is the
same, it is likely correct. If these methods prove problematic
owing to variants of ossiication or segmentation anomalies, the
ultrasound transducer can be used to locate the tip of the conus,
mark the skin at that level with a radiopaque BB marker, and
obtain AP and lateral radiographs of the entire spine to determine
the corresponding vertebral level (Fig. 49.11). If this is done, a
lateral ilm is helpful because distortion from beam angulation
is less problematic. he AP spine view allows counting of ribs
and vertebral bodies with accuracy. he degree of ossiication
of the coccyx can also be assessed with this ilm. As the sonographer
gains experience in scanning the neonatal spine, the
variability in the shape of the cartilaginous coccyx becomes
evident (Fig. 49.12 and Video 49.3).