Diagnostic ultrasound ( PDFDrive )

CHAPTER 49 The Pediatric Spinal Canal 1681
A
B
FIG. 49.13 Tethered Cord in Two Infants. (A) Newborn with tethered cord ending at S2 and an interposed ilar cyst (C). (B) Newborn with
a tethered cord in the setting of the VATER association (vertebral defects, imperforate anus, tracheoesophageal istula, and radial and renal anomalies).
Arrow indicates the point of tethering.
spinal dysraphism) or covered by intact skin (closed spinal
dysraphism) (Table 49.1). he abnormalities can be further
characterized by the presence of a subcutaneous mass, which
can be formed by neural elements, subarachnoid luid, or fat.
Open Spinal Dysraphism
Open defects can occur at any level but are most common in
the lumbosacral region. he diagnosis is oten irst suspected
on maternal screening tests for elevated levels of alpha-fetoprotein
(AFP) during pregnancy in maternal blood or amniotic luid.
Sonography of the fetus being screened for this condition is well
established. 48-50 Open defects are generally repaired on the irst
or second day of life without preoperative imaging because the
defect is readily apparent. Preoperative MRI can be performed
to detect other abnormalities such as syrinx, diastematomyelia,
and hydrocephalus and to understand the relationship between
the placode and nerve roots. 10 Postoperative MRI can be also
done to document associated anomalies. Ultrasound examination
of the newborn spine with unrepaired defects is infrequently
performed, in order to avoid the risk of ulceration or infection.
In transverse prone views one would see the dorsal roots lateral
and the ventral roots medial and posterior to the placode. 12
Ultrasound can be performed to detect other abnormalities of
the spine above the open defect such as syrinx, atrophy of the
thoracic and lumbar cord, arachnoid cyst, diastematomyelia, and
intradural lipoma. Ultrasound and MRI of the brain are usually
obtained to follow up hydrocephalus and Chiari II malformations
before and ater repair.
he most common open spine defect is myelomeningocele
(98% of cases). he true incidence of neural tube defects is diicult
to estimate and is approximately 2 per 1000 live births, with
signiicant geographic and ethnic variations and increased
incidence in certain high-risk groups. 51 he incidence has
decreased over time, possibly the result of periconceptual folic
acid, other environmental factors, and/or termination of afected
pregnancies. 52 A myelomeningocele occurs when a placode is
displaced dorsally by expanded subarachnoid space and is exposed
to the environment by a bony defect in the midline (Fig. 49.14).
Infants with myelocele have a lat neural placode (at the level
of the skin of the back) that is exposed to the environment. he
lack of expansion of the subarachnoid space distinguishes this
lesion from the myelomeningocele (Fig. 49.15).
Hemimyelomeningoceles or hemimyeloceles are very rare
causes of open neural tube defects that can be present if one
side of a split cord malformation fails to neurulate. hey are
likely related to embryologic failures in gastrulation with superimposed
neurulation. 5
Open spinal defects are always associated with the Chiari II
malformation. he proposed mechanism of this association is
that leakage of CSF by the open spinal defect collapses the