Anemia of Prematurity - Portal Neonatal

As described, the primary defect is a failure of the neural folds to fuse in the midline and form the
neural tube, which is neuroectoderm. However, the subsequent defect is the maldevelopment of
the mesoderm, which, in turn, forms the skeletal and muscular structures that cover the underlying
neural structures. These NTD defects can be open (neural structures that communicate with the
atmosphere) or closed (skin covered). They can be ventral or dorsal midline defects.
Pathology
Spina bifida cystica
The 2 major types of defects seen with spina bifida cystica are myelomeningoceles and
meningoceles. Cervical and thoracic regions are the least common sites, and lumbar and
lumbosacral regions are the most common sites for these lesions.
Myelomeningocele is a condition in which the spinal cord and nerve roots herniate into a sac
comprising the meninges. This sac protrudes through the bone and musculocutaneous defect. The
spinal cord often ends in this sac in which it is splayed open, exposing the central canal. The
splayed open neural structure is called the neural placode. This type of NTD is the subject of most
of this article (see Image 1). Certain neurologic anomalies, such as hydrocephalus and Chiari II
malformation (discussed later in this article), accompany myelomeningocele. In addition,
myelomeningoceles have a higher incidence of associated intestinal, cardiac, and esophageal
malformations, as well as renal and urogenital anomalies. Most neonates with myelomeningocele
have orthopedic anomalies of their lower extremities and urogenital anomalies due to involvement
of the sacral nerve roots.
A meningocele is simply herniation of the meninges through the bony defect (spina bifida). The
spinal cord and nerve roots do not herniate into this dorsal dural sac. These lesions are important
to differentiate from a myelomeningocele because their treatment and prognosis are so different
from myelomeningocele. Neonates with a meningocele usually have normal examination findings
and a covered (closed) dural sac. Neonates with meningocele do not have associated neurologic
malformations such as hydrocephalus or Chiari II.
A subtype of spina bifida is called lipomeningocele, or lipomyelomeningocele, which is a common
form of NTD treated by pediatric neurosurgeons. These lesions have a lipomatous mass that
herniates through the bony defect and attaches to the spinal cord, tethering the cord and often the
associated nerve roots. The lipomyelomeningocele can envelop both dorsal and ventral nerve
roots, only the dorsal nerve roots, or simply the filum terminale and conus medullaris. These lesions
do not have associated hydrocephalus but have a more guarded prognosis than simple
meningoceles. The surgical correction of these lesions is more complex, and the retethering rate in
which an additional surgery is required is as high as 20% in some series.
In a third rare type of spina bifida cystica called myelocystocele, the spinal cord has a large terminal
cystic dilatation resulting from hydromyelia. The posterior wall of the spinal cord often is attached to
the skin (ectoderm) and is undifferentiated, thus giving rise to a large terminal skin-covered sac.
The vast majority of the lesions are dorsal, although a small minority (approximately 0.5%) are
ventral in location. The most common ventral variant is an anterior sacral meningocele, which most
often is discovered in females as a pelvic mass.
Spina bifida occulta
In this group of NTDs, the meninges do not herniate through the bony defect. This lesion is covered
by skin (ie, closed), therefore rendering the underlying neurologic involvement occult or hidden.
These patients do not have associated hydrocephalus or Chiari II malformations. Often, a skin
lesion such as a hairy patch, dermal sinus tract, dimple, hemangioma, or lipoma points to the
underlying spina bifida and neurologic abnormality present in the thoracic, lumbar, or sacral region.
Presence of these cutaneous stigmata above the gluteal fold signifies the presence of an occult
spinal lesion. Dimples below the gluteal fold signify a benign, nonneurologic finding such as a
pilonidal sinus. This is an important point for differentiating the lesions that have neurologic
involvement from those that do not.