DOI:10.2214/AJR.05.2160
AJR 2007; 188:739-744
© American Roentgen Ray Society
Sonography of the Neonatal Spine: Part 2, Spinal Disorders
Lisa H. Lowe1,2,
Andrew J. Johanek1,3 and
Charlotte W. Moore1,2
1 Department of Radiology, The University of Missouri-Kansas City, Kansas City,
MO.
2 Department of Radiology, Children's Mercy Hospital and Clinics, 2401 Gillham
Rd., Kansas City, MO 64108.
3 Department of Radiology, St. Luke's Hospital, Kansas City, MO.
Received December 16, 2005;
accepted after revision February 28, 2006.
Address correspondence to L. H. Howe
(lhlowe{at}cmh.edu).
Awarded Bronze Medal poster exhibit at the 2005 annual meeting of the
American Roentgen Ray Society, New Orleans, LA.
CME
This article is available for CME credit. See
www.arrs.org
for more information.
FOR YOUR INFORMATION
The reader's attention is directed to part 1 accompanying this article,
titled "Sonography of the Neonatal Spine: Part 1, Normal Anatomy,
Imaging Pitfalls, and Variations That May Simulate Disorders," which
begins on page 733.
FOR YOUR INFORMATION
This article is available for CME credit. See
www.arrs.org
for more information.
Abstract
OBJECTIVE. The objective of part 2 of this article is to focus on
key imaging features of common skin-covered spinal anomalies (spina bifida
occulta) and to distinguish them from normal variants (previously discussed in
part 1).
CONCLUSION. Modern imaging technology allows accurate neonatal
spinal sonographic screening and the characterization of spinal abnormalities
within the first few days of life. It is useful to determine the type of
lesion present and to guide the type and timing of therapy.
Keywords: neonatal imaging • neuroradiology • pediatric radiology • sonography • spine
Introduction
Congenital spinal anomalies are the result of three basic abnormal
embryologic processes (see part 1 of this article under Embryology). First,
premature separation of the skin ectoderm from the neural tube can lead to
entrapment of mesodermal elements, such as fat. Second, failed neurulation
leads to dysraphisms, such as myelomeningocele. Last, anomalies of the filum
terminale, such as fibrolipomas and caudal regression syndrome, are caused by
disembryogenesis of the caudal cell mass
[1-3].
Classification
Congenital spinal dysraphisms can be classified on the basis of the
presence or absence of a soft-tissue mass and skin covering
[2]. Those without a mass
include tethered cord, diastematomyelia, anterior sacral meningocele, and
spinal lipoma. Those with a skin-covered soft-tissue mass include
lipomyelomeningocele and myelocystocele. Those with a back mass but without
skin covering include myelomeningocele and myelocele. Several common disorders
will be discussed in this article, including tethered cord, spinal lipoma,
lipomyelomeningocele, fatty filum and filar fibrolipoma, and caudal regression
syndrome. Finally, the usefulness of sonography in failed lumbar puncture with
subdural hematoma will be discussed.
Tethered Cord
Tethered cord, or low-lying conus medullaris, is caused by incomplete
regressive differentiation and failed involution of the terminal cord.
Symptoms occur because of traction on the abnormally anchored filum terminale
and adjacent nerve roots. Children with tethered cord may present at any age
with difficulty ambulating, weakness, stiffness, abnormal reflexes, bladder
dysfunction, and, less often, bowel dysfunction
[2].
Sonographically, tethered cord is diagnosed in neonates by the presence of
a low-lying conus (below the L2-L3 disk space) and lack of normal nerve root
motion during realtime sonography
[4,
5] (Fig.
1A,
1B). However, in older
patients, clinical correlation is required because the conus may be normally
positioned but still be tethered (tight filum syndrome)
[6]. In this situation,
assessment of normal nerve root motion, whenever possible, at real-time
imaging is more important [1,
6].
Other associated spinal findings include a thickened filum terminale,
fibrolipoma, spinal dysraphism, syringomyelia, scoliosis, congenital spinal
masses (lipomas, dermoids), cysts (myelocele), and sinus tracts that contain
fluid (Fig. 2A,
2B). Other nonneurologic
anomalies are common as well, including tracheoesophageal fistula, congenital
heart disease, and renal anomalies (VATER syndrome).
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Fig. 2A —Syrinx and tethered cord in 1-week-old girl with imperforate anus
and scoliosis. Longitudinal sonogram reveals low-lying conus at L4 vertebra
with hypoechoic cystic space (arrow) expanding lumbar spinal
cord.
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Fig. 2B —Syrinx and tethered cord in 1-week-old girl with imperforate anus
and scoliosis. Sagittal T2-weighted MR image confirms conus is tethered at S1
level (arrowhead) and lumbar spinal cord contains large,
hyperintense, fusiform syrinx (arrow).
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Treatment centers on surgical release of the filum and preservation of
nerve root function. Early recognition and treatment of tethered cord is
important to preserve normal function, which may be irreversibly lost if
treatment is delayed [6]. The
prognosis varies with the severity of anomalies present. Retethering is common
with normal growth and may require re-release surgery.
Spinal Lipoma
Spinal lipomas are caused by premature disjunction (embryologic separation
of neural ectoderm from cutaneous tissue elements) that allows mesenchyma to
be trapped between the neural folds and remain in contact with the neural
canal [1,
2]. Spinal lipomas are composed
of normal fat, may grow significantly during the first year of life, and may
change in size with weight. They may be intradural, extradural, or a
combination of both. In addition to fat, 84% of lipomas also contain neural
tissue or meninges [2,
3]. Associations include
tethered cord, dysraphism (4%), fatty filum or lipoma of filum (12%), and
vertebral anomalies
[1-3]
(Fig. 3A,
3B). On MRI, the mass follows
fat signal.
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Fig. 3A —Intradural lipoma and tethered cord in 2-week-old girl with hairy
patch on lower back. Longitudinal sonogram reveals typical features of
hyperechoic lipoma (calipers) attached to dorsal aspect of
thoracolumbar spinal cord. Conus is tethered to mass at L3-L4 disk space
(arrow).
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The prognosis of these lesions is varied depending on their ability to be
resected and the presence and type of various associated anomalies. Treatment
consists of resection, when possible, or debulking.
Spina Bifida Occulta with Lipomyelomeningocele
Spina bifida occulta is defined as any skin-covered osseous defect of
posterior elements through which various combinations of neural elements
(neural placode), meninges, CSF, and adipose tissue protrude
[1,
2] (Fig.
4A,
4B,
4C). The cause is defective
disjunction and neurulation with entrapped mesenchyma in contact with the
incompletely closed neural tube. The presentation is usually at an age younger
than 6 months; the disease rarely presents in adulthood.
Lipomyelomeningoceles, with an incidence of two in 1,000, encompass 20% of
skin-covered lumbosacral masses and 20-50% of occult dysraphic spinal lesions
[2,
4]. Treatment and prognosis
depend on the specific anomalies present.
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Fig. 4A —Lipomyelomeningocele in 1-day-old girl with soft-tissue swelling on
lower back. Longitudinal (A) and transverse (B) sonograms show
lumbosacral dysraphism through which spinal cord (straight arrow),
hyperechoic fatty tissue (curved arrow), and hypoechoic CSF
(arrowhead, B) pass.
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Fig. 4B —Lipomyelomeningocele in 1-day-old girl with soft-tissue swelling on
lower back. Longitudinal (A) and transverse (B) sonograms show
lumbosacral dysraphism through which spinal cord (straight arrow),
hyperechoic fatty tissue (curved arrow), and hypoechoic CSF
(arrowhead, B) pass.
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Fig. 4C —Lipomyelomeningocele in 1-day-old girl with soft-tissue swelling on
lower back. T1-weighted sagittal MR image confirms lumbosacral dysraphism with
intra- and extradural adipose tissue (arrows), neural tissue
(arrowhead), and tethered cord.
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Fatty Filum and Filar Fibrolipoma
Fatty filum and filar lipomas are due to a minor anomaly of canalization
and retrogressive differentiation with persistent or dedifferentiated fatty
tissue [2]. Minimal fat in
filum is often asymptomatic and has been seen in 6% of normal spines at
autopsy [1] (Fig.
5A,
5B). It is considered a normal
variant when it is an isolated finding in a normal-size filum (< 1-2 mm)
[1,
4]. When the fatty tissue forms
a mass, a filar lipoma is diagnosed. Associated anomalies include
myelomeningocele and tethered cord. The treatment and prognosis vary depending
on the clinical symptoms and specific anomalies present.
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Fig. 5A —Fatty filum in 23-week-old boy with sacral dimple who is otherwise
developmentally normal. Longitudinal sonogram shows focus of segmental
increased echogenicity within filum (arrowhead) posterior to L4
vertebral body.
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Fig. 5B —Fatty filum in 23-week-old boy with sacral dimple who is otherwise
developmentally normal. Axial T1-weighted MR image confirms fat in filum as
localized area of increased signal intensity (arrowhead).
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Caudal Regression Syndrome
Caudal regression syndrome, which is thought to be due to abnormal
mesodermal formation of the caudal cell mass (possibly from hyperglycemia),
affects one in 7,500 children
[3]. It occurs most often in
children of diabetic mothers (Fig.
6A,
6B) and is also associated
with various other genitourinary, anal, vertebral, and limb anomalies
[1,
3]. The presentation and
imaging appearance vary with the degree of deformity, ranging from minimal to
severe regression of the coccyx, sacrum, and lumbar spine. Progressive absence
of bone structures occurs in a caudal to cranial direction
[1] (Fig.
6A,
6B).
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Fig. 6B —Caudal regression syndrome in 3-day-old girl of diabetic mother.
Sagittal T1-weighted MR image confirms blunted conus medullaris and associated
fat in filum (arrow) as well as absence of sacrum and coccyx
(arrowhead).
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Subdural Hematoma
Subdural hematoma is uncommon in neonates; it may be iatrogenic after
failed attempts at neonatal lumbar puncture
[7]. Sonography is useful to
determine whether the thecal sac is compressed by a hematoma. If it is not,
sonography can be used to determine the best timing and level for a potential
reattempt at lumbar puncture
[7] (Fig.
7A,
7B).
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Fig. 7A —Subdural hematoma in febrile 2-month-old boy after multiple attempts
at lumbar puncture. Longitudinal sonogram identifies hemorrhage as
circumferential, echogenic material in subdural space (straight
arrow) that displaces dura (curved arrows) from posterior
elements (arrowhead) and collapses normal CSF-containing thecal
sac.
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Fig. 7B —Subdural hematoma in febrile 2-month-old boy after multiple attempts
at lumbar puncture. Transverse sonogram also reveals circumferential echogenic
subdural blood (arrows) obliterating normal CSF, which contains
thecal sac.
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Conclusion
Modern sonography technology allows accurate screening and characterization
of spinal abnormalities during the first few days of life. It is useful for
determining the type of lesion present in order to guide the type and timing
of intervention.
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Abstract
Introduction
