Diagnostic ultrasound ( PDFDrive )

CHAPTER 35 The Fetal Spine 1223
FIG. 35.9 Lateral Longitudinal Scan Plane. (A) Diagram shows
the incident sound beam (arrows) relecting off the lateral surface of
the near pedicle and the medial surface of the far pedicle. Therefore
this scan plane will show the cross section of the pedicles of each
vertebra but not the centrum and laminae. The red structures are
ossiied portions of the vertebra. (B) Lateral longitudinal scan of the
lumbar spine at 16 weeks shows the ossiied pedicles (short arrows).
The lumbar pedicles usually form a series of parallel echogenic foci,
although they may normally diverge by 1 to 2 mm. Note the faint
echogenic structures between the pedicles; these represent echoes
from the centra that intercept the edge of the insonating beam (long
arrow, iliac wing). (C) When the tomographic scan plane is thick or is
placed closer to the centrum, the pedicles and centra may be visualized
simultaneously. The centra will appear as an extra set of echogenic
dots (arrows) between the series of pedicles. (D) Three-dimensional
scan of a 19-week fetus shows the ossiied spinal elements from
the cervical area to the lumbosacral level, as viewed from the posterior
aspect of the fetus. The 12 ribs are visualized. L1 vertebra is immediately
caudal to the 12th rib level (arrows). (D courtesy of Siemens
Ultrasound.)
A
B C D
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helpful in localizing spinal defects accurately by using simultaneous
multiplanar imaging and referencing to the volume-rendered
image. 25,28 For determination of spinal level, T12 is taken to be
the most caudal vertebra with a corresponding rib. hreedimensional
ultrasound may also show concomitant rib deformities
in the setting of spinal abnormalities and is useful for
counseling prospective parents by providing a more understandable
visual demonstration of the skeletal abnormality.
SPINA BIFIDA
Spina biida implies a physical defect in the structure of the
spinal canal that may result in a protrusion of its contents
(meninges, cerebrospinal luid, and neural tissue) (Table 35.3).
hese defects usually occur along the dorsal midline (most oten
in the lumbosacral area) but in rare cases may occur
anteriorly.
Open NTDs occur in less than 0.5 per 1000 births in North
America and with higher frequencies in other geographic areas.
Hispanic women in the United States have a higher incidence
of births afected by NTDs, possibly because of a higher prevalence
of a mutation in the methylenetetrahydrofolate reductase deiciency
gene. 35 In one area of China, the overall prevalence of
NTDs in 2003 was 13.9 per 1000 live births. 36 In recent years,
however, there has been a decline in the incidence of NTDs.
Some of this decline may be attributed to screening programs,
which include measurement of MS-AFP and performance of
second-trimester ultrasound. 37,38
Protocol to Evaluate Spina Biida With Three-
Dimensional Volume Data
Volume data are acquired from sagittal and transverse
sweeps through the spine.
Volume data are reformatted to display standardized
multiplanar views of the fetal spine.
Three-dimensional reconstruction of the fetal spine (with
maximum-intensity projection ilter) visualizes the
ossiied spinal elements.
To determine spinal level, the 12th thoracic (T12) is taken
to be the most caudal vertebra with a corresponding
rib.