Diagnostic ultrasound ( PDFDrive )

1682 PART V Pediatric Sonography
TABLE 49.1 Clinical-Radiologic
Classiication System for Spinal Dysraphism
OPEN SPINAL DYSRAPHISM
Myelomeningocele (or hemimyelomeningocele)
Myelocele (myeloschisis)
CLOSED SPINAL DYSRAPHISM
With a Subcutaneous Mass
Lipomyelomeningocele
Lipomyelocele
Myelocystocele (terminal or cervical)
Meningocele
Cervical myelomeningocele
Without a Subcutaneous Mass
Simple dysraphic states
• Spina biida
• Persistence of terminal ventricle
• Intraspinal lipoma
• Tight ilum terminale
Complex dysraphic states
• Dorsal dermal sinus
• Caudal regression syndrome
• Split notochord syndrome (dorsal enteric istula and
neurenteric cyst)
• Split cord malformation (diastematomyelia)
• Segmental spinal dysgenesis
Modiied from Barkovich AJ. Pediatric neuroimaging. 4th ed.
Philadelphia: Lippincott Williams & Wilkins; 2012. 36
embryonic ventricular system and the lack of distention disrupts
normal brain development. 53 he indings of hindbrain herniation
can be mild early in pregnancy, 54 and although indings may
progress, the severity of the hindbrain malformation varies and
can lead to delay in diagnosis if the spinal abnormality is not
recognized. he Chiari II malformation is absent in all types of
closed spinal defects with the possible exception of large myelocystoceles.
5 he Chiari II malformation consists of a small
posterior fossa with upward transincisural herniation of the
superior cerebellum, as well as downward herniation through
the foramen magnum with associated compression and distortion
of the brainstem. his posterior fossa distortion can be seen by
sonography of the brain through the anterior fontanelle and of
the craniocervical junction through the foramen magnum. 55
Hydrocephalus may develop early in the second trimester but
usually develops postnatally, typically ater closure of the skin
opening because this closes the CSF leak. 56 Sonography also has
a potential role in the evaluation of the spinal cord in patients
with repaired myelomeningocele. Speciically, real-time imaging,
cine clips, or M-mode ultrasound, in conjunction with MRI, has
the potential to suggest the redevelopment of the tethered cord
syndrome, based on dampened nerve root pulsation in this
high-risk group. he scarring that adheres the caudal cord to
the dura rarely occurs in neonates. he cord should be central
in the dependent portion of the canal, and cord and roots should
move normally in both the anterior-posterior direction with
normal respiration and craniocaudally with neck lexion. 12,57-60
Closed Spinal Dysraphism With
a Subcutaneous Mass
Closed spinal dysraphisms are deined as the group of spinal
dysraphisms that exist beneath an intact covering of dermis and
epidermis and that are therefore not discovered with AFP screening.
Many patients are clearly identiied by abnormal physical
examination indings, but some defects are not clinically evident
at birth and may manifest later in infancy (around 6 months of
age) with tethered cord syndrome. Common closed spinal defects
that manifest with a lumbar subcutaneous mass include lipomas
with a dural defect (lipomyelocele and lipomyelomeningocele)
and rare entities including meningocele and terminal myelocystocele.
he main diferential diagnosis for lumbar masses is
sacrococcygeal teratoma and overgrowing fatty tissue in caudal
regression. Cervical masses that occur as a closed dysraphism
with a subcutaneous mass are very rare and include cervical
myelomeningocele, myelocystocele, and meningocele. he differential
diagnosis includes occipitocervical cephalocele and
subcutaneous lymphatic malformations.
In lipomyelocele (lipomyeloschisis; Fig. 49.16, Video 49.4,
Video 49.5, and Video 49.6), the neural placode-lipoma interface
is within or at the edge of the spinal canal and the associated
lipoma is continuous with the subcutaneous fat through a
posterior bony defect; the overlying skin is frequently abnormal.
he subcutaneous fatty mass is located above the intergluteal
crease and usually extends asymmetrically into one buttock. he
placode is terminal (apical or parietal) and may be asymmetrical,
involving one edge of the neural plate. he placode-lipoma
interface may extend over several vertebral levels. he size of
the spinal canal may be increased depending on the size of the
lipoma, but the size of the subarachnoid space ventral to the
cord is normal. 10
In lipomyelomeningocele, the ventral subarachnoid space
is enlarged, the interface of the placode-lipoma is outside the
spinal canal, and the lipoma is continuous with the subcutaneous
fat through a posterior bony defect (Fig. 49.17, Video 49.7, Video
49.8). he placode is frequently segmental and may be deformed,
stretched and rotated asymmetrically toward the lipoma on one
side, with meninges herniating on the opposite side; therefore
the lengths of the spinal roots can be asymmetrical. he spinal
cord below the placode is normal and lies within the canal.
In both entities of lipomyelocele and lipomyelomeningocele,
the mass is more commonly formed by mature adipocytes separated
by collagen bands. Other tissues such as aberrant neuroglial
tissue, cartilage, bone, or ibrous, muscular, or vascular structures
can be present and form “dysraphic hamartomas.” he lipoma
can invade the extradural space (lipomatous dura mater) and
hydromyelia can be present. he subcutaneous and intraspinal
components of the lipomas can grow as part of normal increase
in adipose tissue in childhood, with obesity or pregnancy.
A posterior meningocele is less common than lipomyeloceles
and lipomyelomeningoceles and forms from extension of a
CSF-illed sac lined by dura and arachnoid through a dorsal
bony defect. Nerve roots or part of the ilum terminale may
course in the sac, but no part of the spinal cord is in the sac.
he spinal cord itself is normal but can be tethered to the neck