SPINAL DYSRAPHISM
The more benign forms of spinal dysraphism include occult bony abnormalities unaccompanied by any displacement of spinal canal contents and with or without cutaneous stigmata. In these cases, there is failure of bony fusion between the two laminae of the involved vertebra (see Plate 1-7). Spina bifida occulta is of no clinical significance when it occurs alone without intra-spinal involvement.
Cutaneous stigmata of spina bifida
occulta include dimples, dermal sinuses, subcutaneous lipomas, tufts of hair,
or hemangiomas. Cutaneous lesions may occur in isolation, or herald an
underlying tethered cord due to a low-lying conus or fat-infiltrated filum.
Only a small subset of cutaneous lesions is associated with an intra-spinal
anomaly, and MRI performed within a few months of age can often exclude the
diagnosis without radiation or sedation. The tethered spinal cord syndrome occurs
when a hypertrophied filum terminale is too inflexible and causes progressive
traction and relative caudal displacement of the conus medullaris as the spine
grows. This traction can produce progressive ischemia in the conus medullaris
and lead to symptoms of sphincter dysfunction and gait abnormalities. One third of infants with a congenital tethered
cord are likely to eventually develop neurologic dysfunction if the tethered
cord is not treated. Prophylactic detethering by microsurgical sectioning of
the filum terminale, ideally before 1 year of age, allows immediate ascent of
the conus medullaris toward a more normal location within the spinal canal and
minimizes the chance of development of neurologic deficits as the spine grows.
For older children who have a late symptomatic presentation, treatment may
minimize the further progression of neurologic
deficits. If spina bifida occulta occurs in conjunction with a dermal sinus (an
epithelium-lined tract linking the dural sac with the skin surface), there is a
potential for communication between the skin and intraspinal contents and
subsequent infection. Dermal sinuses located above the sacrococcygeal region
should be removed surgically after MRI imaging to evaluate for other associated
lesions.
SPINA BIFIDA APERTA
Dysraphic conditions in which there
are overt manifestations of the underlying bony defect are referred to as
“spina bifida aperta” (see Plate 1-8). Within this group, the progression of
neurologic sequelae is defined, to a large extent, by the degree to which the contents
of the spinal canal are displaced from their normal location. In the case of a meningocele,
the most benign form of spina bifida aperta, a meningeal cyst free of
neural elements is extruded. Often, a meningocele can
be completely removed surgically and the defect closed.
Diastematomyelia is a congenital malformation in which the spinal
cord is split into two sections, or hemicords. It is frequently associated
with a midline cutaneous tuft of hair, and all infants with a worrisome tuft
should be screened with an MRI. Frequently, a bony or cartilaginous septum
separates the divided sections. Patients with a split cord malformation are at
risk of developing associated scoliosis and progressive myelopathy as the spine
grows. Surgical excision of the midline septum can halt the deteriorating
condition and, in some cases, lead to restored function.
A far more devastating variant of
spina bifida aperta is myelomeningocele, in which the spinal cord or
nerve roots, or both, protrude through the posterior bony and cutaneous defects
due to failed closure of the posterior neuropore. The severity of deficits from
a myelomeningocele correlates with its location along the spinal canal, with
increasing deficits occurring with more rostral lesions. The neurologic deficits
are due to abnormal in utero development throughout the entire CNS.
Postnatal closure of the myelomeningocele in the term infant is performed
within a few days of birth to minimize the risk of meningitis, and is
associated with low morbidity. Prenatal fetal closure may be an option for a
very select group of patients and is associated with complications, including
preterm delivery.
Prenatal folate supplementation has
markedly decreased both the incidence of infants born with myelomeningocele and
lesion severity. Infants with sacral and low lumbar lesions often achieve some
degree of ambulation, and approximately 80% can achieve social bladder and
bowel continence. Approximately half of
infants with a lumbar or sacral myelomeningocele will develop hydrocephalus
that requires surgical treatment (see Plate 1-7). Most of these infants will
have an associated Chiari II malformation, with displacement of the
cerebellar vermis into the cervical canal, but only a few percent will become
symptomatic at any point. Children are at risk for developing the tethered cord
syndrome as the myelomeningocele scar adheres to
the repair site while the spine grows. All repaired myelomeningoceles will
appear adherent to some degree on MRI, and the diagnosis of a tethered cord in
this population is made clinically. Although multidisciplinary care is needed
throughout the life span of children born with a myelomeningocele, many will
become in ependent productive adults with a good quality
of life.
