Diagnostic ultrasound ( PDFDrive )

CHAPTER 35 The Fetal Spine 1233
diicult to portray unequivocally. he lemon sign spontaneously
resolves in the third trimester. 78 In addition, it is seen in 1% of
normal fetuses. 77,78 he lemon sign should prompt detailed
examination of the posterior fossa, to search for obliteration of
the cisterna magna and for the banana sign, and the fetal spine,
for direct evidence of spina biida.
Associated Noncranial Abnormalities
Foot deformities, primarily clubfoot, and dislocation of the
hips are frequently associated with spina biida. 80 hese abnormalities
are caused by imbalanced muscular actions resulting from
peripheral nerve involvement with the NTD. In fetuses with
open spina biida, 24% demonstrate additional morphologic
abnormalities on second-trimester sonography, such as renal
abnormalities, choroid plexus cysts, cardiac ventricular septal
defect, omphalocele, and intrauterine growth restriction. 58
Sonographic Signs of Spina Biida
Nonvisualization of cisterna magna
Deformation of cerebellum (banana sign)
Concave frontal bones (lemon sign)
Dilation of the lateral ventricles
Chiari II malformation (97%)
Biparietal diameter lower than expected
Prognosis
It is diicult to predict the long-term prognosis in a fetus with
an identiied myelomeningocele. However, the outcome is better
for low lesions (lower lumbar or sacral), closed defects, and those
with minimal or no hydrocephalus and no compression of the
hindbrain from Chiari II malformation. 55,66,75,81 In more than
880 patients 82 of live deliveries with spina biida, about 85%
survived past age 10, and 2% died in the neonatal period. Of
the survivors, about 50% had some type of learning disability.
About 25% of survivors had an intelligence quotient (IQ) above
100, with about 75% above 80. About 33% of survivors developed
symptoms and signs related to pressure on the hindbrain and
brainstem (e.g., pain, weakness, and spasticity in arms), and
some required cervical laminectomy to relieve the pressure. Wong
and Paulozzi 83 found 5-year survival rates of 82.7% for 1979-1983,
88.5% for 1984-1988, and 91.0% for 1989-1994. Determining
prognosis for survival for current newborns is more diicult
because of medical and surgical advances since studies describing
patients born in the 1960s, 1970s, and 1980s. 2
Beyond survival, multiple impairments may afect the individual,
including motor dysfunction, bladder and bowel dysfunction,
and intellectual impairment. 2 Degree of muscle dysfunction
is deined by the highest level of the open NTD, not by the
number of involved vertebrae or the size of the overlying sac.
When the lesion is thoracic, the legs are without muscle function,
and when it is upper lumbar (L1-L2), useful leg function is
minimal. When the upper level is L3-L5, the prognosis for longterm
walking and the need for assistive devices are diicult to
predict. hose with sacral defects will usually be able to walk
well but with imperfect gait. Almost all people with spina biida,
including those with sacral defects, will have some degree of
bowel and bladder dysfunction.
It is very diicult to predict the ultimate level of intellectual
functioning. In general, those who do not require ventricular
shunting have much better outcomes for intellectual functioning.
In those requiring shunts, the average IQ is approximately 80,
which is low-normal range. 84 he rate of profound intellectual
impairment (IQ < 20) in those with shunts is 5%, usually related
to medical complications such as shunt infections and Chiari II
efects (e.g., apnea, hypoxia).
Fetal Surgery for Myelomeningocele
he irst fetal surgery for repair of myelomeningocele was
performed in 1997. A formal clinical trial was performed from
2003 to 2010, with early termination of the study due to positive
fetal results (decreased hindbrain herniation/need for shunt and
improved spinal level of function). However, families and clinicians
must evaluate the potential for improved function for the
child against the risks of fetal/maternal surgical morbidity, most
commonly preterm delivery and uterine dehiscence. 85 Fetal
myelomeningocele is a nonlethal entity; in utero surgery for
repair of myelomeningocele is potentially lethal. 86
Although myelomeningocele is a primary embryologic disorder,
neurologic damage is also secondary to progressive in
utero damage to the exposed spinal cord. he development of
techniques to close open NTDs before birth has generated great
interest and hope for fetal interventions and outcomes. Prior to
the 2003 trial, preliminary observations from two centers suggested
that improvements may occur not in spinal cord function
as originally postulated 87 but in the extent of the hindbrain
herniation and the frequency that shunting is required to control
hydrocephalus. In a report of 25 patients who underwent
intrauterine myelomeningocele repair at Vanderbilt University,
no improvement in leg function resulted from the surgery, but
there was a substantially reduced incidence of moderate to severe
hindbrain herniation (4% vs. 50%) and a moderate reduction
in the incidence of shunt-dependent hydrocephalus (58% vs.
92%). 88 he number of U.S. centers is limited to prevent the
uncontrolled proliferation of new centers ofering this complex
multidisciplinary procedure. 89 Prospective parents electing
surgery 90 should weigh the potential beneits against the potential
risks. 90-93
MYELOCYSTOCELE
Myelocystocele is an uncommon form of spinal dysraphism.
here is dilation of the central canal of the spinal cord. he
central canal herniates posteriorly through the spinal cord and
through the posterior neural arch to form an exterior sac. here
may be no associated spina biida lesion.
he sac is composed of three layers, from inner to outer: the
hydromyelia sac, which is lined by spinal canal ependyma; the
meningeal layer, which is contiguous with the meninges around
the spinal cord; and the skin. he luid within the inner sac is
continuous with the luid of the central canal of the spinal cord;
the luid between the hydromyelia sac and the meningeal layer
is continuous with the subarachnoid luid.