Diagnostic ultrasound ( PDFDrive )

CHAPTER
49
The Pediatric Spinal Canal
Ilse Castro-Aragon, Deborah Levine, and Carol M. Rumack
SUMMARY OF KEY POINTS
• Spine ultrasound is used in the evaluation of neonates and
infants (up to 3-4 months) with high- or moderate-risk
cutaneous manifestations of closed spinal dysraphism,
clinical signs of a tethered cord, or congenital anomalies
that are frequently associated with spinal dysraphism.
• Additional indications for spine ultrasound include
evaluation after failed lumbar puncture, guidance for
lumbar puncture, and intraoperative guidance.
• The conus medullaris is usually at L1-2 and can extend to
the superior endplate of L3.
• Neural tube defects can be open (nonskin-covered) or
closed (skin-covered) spinal lesions, with or without a
subcutaneous mass or other cutaneous stigmata.
• Understanding anatomy, embryology, normal variants,
and scanning technique is important for accurate
diagnosis.
CHAPTER OUTLINE
EMBRYOLOGY
SONOGRAPHIC TECHNIQUE AND
NORMAL ANATOMY
SPINAL ANOMALIES
Tethered Spinal Cord
SPINAL DYSRAPHISM
Open Spinal Dysraphism
Closed Spinal Dysraphism With a
Subcutaneous Mass
Closed Spinal Defects Without a
Subcutaneous Mass
Simple Dysraphic States
Complex Dysraphic States
(Disorders of Gastrulation)
TUMORS
HEMORRHAGE AND INFECTION
ARACHNOID CYSTS
INTRAOPERATIVE AND OTHER USES
OF SPINAL SONOGRAPHY
In normal infants, the spinal canal and contents can be visualized
because the nonossiied state of the posteromedian intraneural
synchondrosis provides an ample acoustic window (Fig. 49.1).
he abnormal coniguration of vertebral bodies in infants with
certain dysraphic abnormalities opens the window even further.
Although magnetic resonance imaging (MRI) is considered the
examination of choice when evaluating the spine in children
and adults, sonography of the spine in the newborn period can
reveal details that are diicult to deine with MRI. Several authors
have recommended ultrasound as the initial imaging modality
in patients younger than 6 months suspected of having a spinal
disorder. 1 Others have recommended ultrasound in asymptomatic
infants with cutaneous stigmata and MRI in the presence of
deicits and cutaneous stigmata. 2 Fatty masses, cord position,
and relationship of the cord to any mass, as well as presence or
absence of nerve root pulsations, can be seen clearly.
EMBRYOLOGY
For a better understanding of spinal pathology, a general knowledge
of the process of spinal cord and vertebral column formation
is helpful. he trilaminar disc is formed by gastrulation. his
is followed by primary neurulation, which forms the spinal
cord from cervical through S5 sacral segments. 3 Distal to this
level, the conus and the ilum terminale are formed by a process
termed canalization and retrogressive diferentiation of the
caudal cell mass, also referred to as secondary neurulation.
During weeks 2 and 3, the bilaminar embryonic disc (formed
by layers of endoderm and ectoderm) is converted into a trilaminar
disc through the process of gastrulation. he process
starts with the appearance of the primitive streak, which forms
caudally, adjacent to the area that eventually becomes the cloaca.
he primitive streak actively forms mesenchymal cells that give
rise to the mesoderm. Some mesenchymal cells migrate laterally,
and the paired anlagen eventually fuse in the midline to form
the notochord process, which contains a central lumen (notochordal
canal). 4,5 he neuroenteric canal, which is the proximal
part of the notochordal canal, normally obliterates when development
of the notochord is complete.
he nervous system develops from the neural plate, which
diferentiates from the ectoderm overlying the notochord and
paraxial mesoderm. 6 he neural plate is composed of neural
ectoderm and is contiguous with the cutaneous ectoderm on
both sides. he cells at the junction of the neural and cutaneous
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