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200
Chapter 5 Anomalies of Dorsal Induction
B
A
Figure 5–25. A transabdominal volume was obtained at 16 postmenstrual weeks of a fetus with an ante-
rior encephalocele. This fetus was part of a twin pregnancy; the other fetus was normal. (A), (B) Volume
displayed using the tomographic feature. In (A), median as well as parasagittal sections of the face are seen,
showing an anterior facial mass (encephalocele). The large skull defect ( arrow ) as well as the brain extending
into the mass is apparent. In (B), the orbits ( small arrows ) are seen to be widely separated by the encephalocele.
(C) The surface rendering of the face reveals an abnormality with a large irregular mass (encephalocele) between
the eyes.
Most fetuses with Meckel-Gruber syndrome are either
stillborn or die within the first day of life due to the dysplastic kidneys that result in oligohydramnios and in turn
result in hypoplastic lungs, although prolonged survival up
to 28 months has been reported.
98
Kaplan et al
99
reported
on a rare case of survival of a child with prenatally diagnosed Meckel syndrome variant. In that case, the child had
an occipital cephalocele and a unilateral multicystic kidney,
with the remaining kidney having normal renal function.
Walker-Warburg Syndrome (Lissencephaly
Type II, HARD (±E) Syndrome)
The descriptive acronym for this syndrome, HARD
(±E), refers to the distinguishing features of this
entity: hydrocephaly, agyria (lissencephaly), retinal
dysplasia, Dandy-Walker malformation, and at times
encephalocele. Cephalocele is not considered diagnostic for Walker-Warburg syndrome and is seen in
∼26.7% of cases reported.
100
Walker-Warburg syndrome
is caused by mutation in the genes encoding protein
O-mannosyltransferase-1 (POMT1); and -2 (POMT2;
gene map locus 14q24.3, 9q34.1, 9q31, 22q12.3-q13.1,
19q13.3). The prognosis of newborns with the syndrome
is dismal
100 , 101
( Figure 5–31 ).
Knobloch Syndrome
Knobloch is a rare syndrome characterized by vitreoretinal
degeneration and occipital encephalocele. This automosal
syndrome is caused by mutation in the collagen XVIII,
alpha-1 polypeptide ( COL18A1 gene; gene map locus
B
21q22.3). The encephalocele is mild and contains only a
small amount of dysplastic glial or neuronal tissue. Usually
there is normal cognitive development; however, eye
pathology may be severe.
102
Sonographic Diagnosis
The sonographic appearance of an occipital cephalocele
is that of a sac-like structure adjacent to the fetal head.
The cephaloceles show a range in size not only of the
skull defect but also of the cephalocele sac itself. The size
of the cephalocele may range from a few millimeters to
a mass exceeding the size of the normal cranial vault.
In infants the size distribution of cephaloceles are as follows: 16% are >20 cm, 14% are between 15 and 20 cm,
12% are between 10 and 15 cm, 30% are between 5 and
10 cm, and 28% are <5 cm.
and BPD may be significantly smaller than expected for
the fetal age. Microcephaly was reported to occur in 9%
to 24% of cases,
in 47% of in utero cases.
agenesis of the corpus callosum, Dandy-Walker cyst,
holoprosencephaly (lobar), and Arnold-Chiari type II
malformation.
a defect through which the contents of the cephalocele sac
communicate with the intracranial portion of the brain
structures. The sac may contain brain tissue (encephalocele) ( Figure 5–18 ), or it may be sonolucent, containing
only CSF (meningocele).
∼10% to 20% of occipital lesions.
often present in the encephalocele sac are the occipital
78
and ventriculomegaly was reported
78
Closer inspection of the cranium reveals
104
55 , 105 , 106
C
103
78
The head circumference
Other malformations are
Meningoceles account for
11
The brain tissues most
BC
Chapter 5 Anomalies of Dorsal Induction
A
201
A
B
C
F
D
F
E
D
E
F
HI
G
H
I
Figure 5–26. Anterior encephalocele at 35 weeks, 3 days. The patient was referred for a second-opinion US because of a suspected large subarachnoid
cyst and microcephaly. (A)–(C) Hypertelorism is noted with a hyperchogenic mass protruding between the fetal orbits. IOD, interorbital distance; OOD,
outer orbital distance. (D)–(G) Serial coronal sections from anterior to posterior of the fetal brain. (D) Frontal–1 section showing an irregularly shaped
head and interhemispheric fissure. (E) Frontal–2 section here a sonolucent structure ( arrow ). (F), (G ) The hemispheres are not symmetrical, and the
ventricle is dilated and contains some adhesions. (H) Median section showing the cranial defect ( arrow ) through which the brain tissue has herniated.
( I) Left oblique–1 sections showing the unilateral hydrocephaly.
202
Chapter 5 Anomalies of Dorsal Induction
J
Figure 5–26. (continued) (J)–(M) Magnetic resonance imaging of the neonate. (J), (K) Coronal sections showing a large cystic area in addition to the
encephalocele ( arrow ).
K
Chapter 5 Anomalies of Dorsal Induction
203
L
Figure 5–26.
cephaly. (M) Axial section showing the nasoethmoidal skull defect
( arrow ) through which the brain is herniating. (N) Picture of the neonate
at the time of surgical correction of the encephalocele. At birth, the
neonate had multiple problems, including severe anemia, seizures, tonic
posturing, and abnormal tongue movements. A ventriculoperitoneal
shunt was subsequently placed. By the eighth month of life, the infant
had had multiple hospital admissions and her problems included diabetes
insipidus, epilepsy, and temperature instability.
(continued) (L) Sagittal section showing unilateral hydro-
M
N
204
Chapter 5 Anomalies of Dorsal Induction
A
B
C
D
Figure 5–27. Anterior encephalocele in a fetus at 36 postmenstrual weeks. (A) Serial sections in the sagittal plane showing the profile and a mass
bulging to distort the normal shape of the profile ( arrows ). (B) Median section of the face showing the sonolucent bulge marked by arrows just behind
the prominence of the nose. (C) Median section of the brain showing the typical sunburst appearance of the gyri above the space representing the third
ventricle. This is typical of the sonographic image of agenesis of the corpus callosum. The posterior horn (PH) is widely dilated. CN, caudate nucleus;
T, thalamus. (D) The neonate clearly showing a distorted face and widely spaced eyes (hypertelorism), as well as a bulge in the midline or somewhat
closer to the left eye. The slight distortion and slight displacement of the nose are evident.
Chapter 5 Anomalies of Dorsal Induction
205
A
D
Figure 5–28.
(A) The profile shows a mass superior to the nose and the nasal bone, as well as the skull defect. Although the brain is not clearly seen, it was normal.
(B) Coronal section through the level of the anterior cephalocele. (C) The rendered face showing the mass. (D), (E) At 32 postmenstrual weeks in the
anterior coronal and median section of the brain (E), a sonolucent space is seen; this is the result of the herniated brain into the cephalocele sac. (F) The
rendered image of the fetus at 32 postmenstrual weeks.
A fetus with an anterior encephalocele was scanned at 25 ( A)–(C ) and 32 ( D), (E ) postmenstrual weeks using 2D and 3D sonography.
B
E
C
F
lobes, which exhibit a normal gyral pattern ( Figure 5–22
and 5–23 ). Approximately half of the cephaloceles situated
“low” in the cervical region contain the occipital lobes of
the hemispheres, but almost all contain the cerebellum.
11
Hydrocephaly may be present in 20% to 65% of cases
as a result of aqueductal stenosis or Chiari III malformation. The corpus callosum is usually present, but it
may also be completely or partially missing. The septum
pellucidum may be absent in up to 80% of cases.
78
Other
associated malformations that may be apparent are cerebellar dysplasia, spinal dysraphism, diastematomyelia,
Klippel-Feil deformity, Dandy-Walker malformation, cleft
palate, microphthalmia, tracheoesophageal fistula, and
cardiac malformations.
32 , 78 , 105 , 107
Early diagnosis of occipital cephalocele is possible
( Figure 5–17 ). Fleming et al
108
reported on the prenatal
diagnosis of an occipital encephalocele using TVS at
12 postmenstrual weeks. It is important to note that some
of the abnormalities associated with occipital cephaloceles
(eg, agenesis of the corpus callosum) may only become
sonographically apparent later on, during the late second
or third trimester of pregnancy.
The sonographic appearance of an anterior cephalocele is that of an irregularly shaped mass protruding
from the fetal face ( Figures 5–24 , 5–25 , 5–26 , 5–27 , and
5–28 ). Associated anomalies include ocular hypertelorism, nasal widening, cleft lip and/or palate, median nasal
fissure, spina bifida, agenesis of the corpus callosum,
206
Chapter 5 Anomalies of Dorsal Induction
Table 5–6. SYNDROMES WITH ACEPHALOCELE
Syndrome Other Features Detectable with Prenatal Ultrasound
Apert Craniosynostosis, short skull base, syndactyly hands and feet, megalencephaly, encephalocele
Craniotelencephalic dysplasia Craniosynostosis, frontal encephalocele at metopic region, microphthalmia, septo-optic
Cranium bifidum occultum Occipital encephalocele
Dyssegmental dysplasia Clefting, encephalocele, micromelia, thick and bowed bones
Facio-auriculo-vertebral Face hypoplasia, cardiac and vertebral anomalies, posterior cephalocele
Fried: Meckel like Lobar holoprosencephaly, large occipital encephalocele, microcephaly, congenital heart disease.
Fronto-facio-nasal-dysplasia Cranium bifidum occultum, anterior cephalocele, cleft lip and/or palate
Frontonasal dysplasia Hypertelorism, frontonasal encephalocele, median cleft lip
Meckel-Gruber Microcephaly, encephalocele, microphthalmia, cleft lip and palate, cystic dysplastic kidneys,
Oculo-encephalo-hepatorenal
Phocomelia-encephaloceleurogenital anomalies
Roberts-SC phocomelia Microbrachycephaly, growth restriction, cleft lip and palate, frontal encephalocele
von Voss-Cherstvoy: limb
defects, thrombocytopenia
Walker-Warburg Type II lissencephaly, cerebellar malformations, vermis hypoplasia, micropthalmia, posterior
Warfarin embryopathy Micropthalmia, cardiac anomalies, occipital encephalocele
dysplasia, agenesis of the corpus callosum, lissencephaly, arhinencephaly
polydactyly
Micrognathia, postaxial polydactyly, cystic renal dysplasia, meningoencephalocele
Bilateral radial aplasia, absent right thumb, fused pelvic kidney, dextroposed heart, hypoplastic
lung, thin corpus callosum, encephalocele
Occipital encephalocele, absent corpus callosum, hypoplastic thumbs, renal agenesis
encephalocele
Data from Hunter AG. Brain and spinal cord. In: Stevenson RE, Hall JG, Goodman RM, eds. Human Malformations and Related Anomalies. Vol 2. New
York: Oxford University Press; 1993:109–137.
ventriculomegaly, and microcephaly.
diagnosis of an anterior cephalocele includes teratoma,
glioma, dermal sinus cyst, facial hemangioma, orbital
duplication, and proboscis.
Three-dimensional ultrasound can render the fetal
face and can therefore be useful in further evaluating
cases in which an anterior cephalocele is present (see
Figures 5–25C and 5–28 ). In addition, rendering can be
applied to other types of cephalocele (see Figures 5–17C ,
5–18 , and 5–19A ). The 3D orthogonal planes as well as
the tomographic US imaging display can aid in the exact
localization and extent of the cephalocele, as well as
in the total evaluation of the intracranial anatomy (see
Figures 5–19A , 5–19B, C , and 5–25 ).
There are no published reports of fetuses with atretic
meningoceles. We have diagnosed two patients with this
condition. In both cases the patients were referred for
evaluation because of the presence of a parietal bone
defect ( Figure 5–32 ). The visualization of an abnormal
falcine artery or an abnormally positioned straight sinus is
indicative of an atretic meningocele and helps in the differential diagnosis.
81
The differential
Risk of Recurrence
The recurrence risk for sporadic (nonsyndromic) occipital
cephaloceles is 1% to 3%; however, if the cephalocele is the
result of an autosomal recessive condition such as MeckelGruber or Walker-Warburg syndrome, the risk is 25%.
Differential Diagnosis
Cephalocele must be distinguished from midline scalp
masses, such as cysts, hemangiomas, nuchal tumors,
cephalohematoma, cystic teratomas, scalp edema, cystic
hygroma, branchiogenic cyst, and fetal hair (during the
third trimester).
109 – 114
In all cases in which a cephalocele is
suspected, a careful search for the cranial defect and possible associated anomalies must be undertaken.
Prognosis
The prognosis for fetuses with a cephalocele depends on
the location, size, and content of the lesion and on the concurrent intracranial as well as extracranial malformations
( Table 5–7 ). The small defects can be easily corrected with
Chapter 5 Anomalies of Dorsal Induction
207
A
O
C
Figure 5–29. Meckel-Gruber syndrome (MGS) at 11 weeks, 3 days. This patient was at high risk for MGS because she had a previous child with this
syndrome. At the time of this scan, a posterior skull defect was seen, as well as a large posterior fossa. There was no polydactyly (similarly, no polydactyly was present in the previous MGS infant). (A), (B) Posterior coronal sections showing a large sonolucent midline cystic area that is freely connected
with the amniotic cavity. (C ) Axial section showing the cranial defect and large cystic structure, which completely fill the area of the posterior fossa. O,
occipital; F, frontal. (D) A view of the right arm and hand of the fetus showing five digits.
surgery, but larger lesions are usually not compatible with
life or may result in a neurologically impaired infant.
reported survival rate for infants with posterior cephalocele ranges from 40% to 75%.
107 , 116 – 118
Mortality is most
115
F
The
B
D
The prognosis for the infant with a parietal cephalo-
cele is the following: ∼33% will die, 40% will have marked
mental retardation, 13% will be able to get an education,
and 15% will develop normally.
104
commonly due to the severity of the other associated malformation or the inability to repair the defect. Meningocele
has a lower mortality rate that ranges from 10% to 25%.
Disabilities occur in the surviving children. Brown et al
reported that 25% of the surviving infants with occipital
cephalocele had severe long-term disability, and 38% had
a mild handicap. These disabilities occurred in their series
Obstetric Management
119
119
Delivery route needs to be individualized after consultation with the appropriate specialists, such as
maternal-fetal medicine, neonatology, and pediatric
neurosurgery.
25
regardless of the defect size, as well as the presence or
absence of brain tissue in the cephalocele.
Anterior cephaloceles appear to carry a relatively better prognosis than other types of cephaloceles. Brown and
Sheridan-Pereira
119
found that 42% of children with anterior
cephaloceles were normal, 17% had mild handicaps, and
25% had severe handicaps. The primary morbidity in children with anterior defects is facial disfigurement, anosmia,
and visual problems.
118 , 120
Surgical procedures for anterior
cephalocele offer only a very limited improvement of the
facial deformity, and many of the children who have survived suffer cosmetic facial and eye deformities.
79 , 85 , 118 , 120 , 121
SPINAL DYSRAPHISM AND
CHIARI II MALFORMATION
Synonyms
Spina bifida, Chiari II malformation, Arnold-Chiari malformation, open NTD
The term Chiari II malformation refers to a constella-
tion of brain anomalies commonly associated with an open
spinal defect; therefore, both entities will be described
together.
208
Chapter 5 Anomalies of Dorsal Induction
A
BC
A
F
E
Figure 5–30.
showing the enlarged anterior horns. (B) Midcoronal–1 section: The severely dilated lateral ventricles are evident. (C) Midcoronal–2 section: The
dangling hyperechogenic choroid plexus is seen (dangling choroid plexus sign); the dilated third ventricle is also seen. (D) Occipital–2 section showing
the cerebellum. (E) Median section with an arrow pointing to a very small encephalocele. (F) Oblique–1 sections through the lateral ventricle; the anterior, posterior, and inferior horns are seen on the same section. The choroid plexus above the thalamus (T) is freely floating in the cerebrospinal fluid.
(G) The additional feature of this syndrome is the postaxial polydactyly ( arrow ). (H) The enlarged multicystic kidneys. (I) The aborted specimen with
the two large kidneys exposed.
E
G
Meckel-Gruber syndrome at 16 weeks, 6 days. The systematic workup of the brain is shown in panels (A)–(F). (A) Frontal–2 section
B
F
H
C
D
I
D
Definition
Spinal dysraphism refers to a defect in which the spine is
open with protrusion of the spinal contents through the
bony defect. Myelocele and myelomeningocele develop
similarly, but the term myelocele refers to a midline plaque
of neural tissue (neural placode) that is flush with the surface and is not covered by skin. In contrast, the myelomeningocele is a bulging defect in which the elevated neural
plate and meninges are contiguous laterally with the subcutaneous tissue.
dysraphic defects are closed, and normal skin covers the
bony defect ( Figure 5–33 ).
Chiari II malformation is a complex anomaly resulting from the presence of open spinal dysraphism in which
there is herniation of the cerebellar vermis and brainstem
through the foramen magnum.
of these structures causes effacement of the cisterna magna
and abnormal placement of the tentorium; hydrocephaly
and reduced amount of extra-axial CSF are usually present.
122
Approximately 10% to 15% of spinal
123 , 124
The abnormal position
Incidence
The birth prevalence of spina bifida in the United States
is 1.90 per 10,000 live births.
downward trend from the 1970s, when the incidence
was reported to be 0.5 to 0.6 per 1000 live births.
Approximately 80% of the lesions occur in the lumbar,
thoracolumbar, or lumbosacral areas of the spine and the
remaining 20% in the cervical and sacral areas.
125
This number reflects a
127
126
Pathogenesis
The onset of myelomeningocele is probably around the
fourth (postconceptual or postmenstrual) week of gestation at the time of closure of the posterior neural tube.
There are four main theories that have been proposed
to explain the varied hindbrain anomalies seen in cases of
Chiari II malformation.
eloquently discussed these four theories: The first theory
is that of Chiari, which attributed the hindbrain herniation
128
Stevenson
128
summarized and
Chapter 5 Anomalies of Dorsal Induction
v
209
A
C
Figure 5–31.
strates the dilated lateral ventricles, V. (B) The posterior encephalocele is seen protruding through the skull defect ( arrow ). (C), (D) Median section of
the fetal brain showing the corpus callosum ( arrow ) and the pericallosal artery ( two arrows ). The brain surface is very smooth, and there is an absence
of the cingulate gyrus that is consistent with lissencephaly.
to hydrocephaly;
A 34-week fetus with Walker-Warburg syndrome. (A) An oblique section was obtained using transvaginal sonography, which demon-
129
however, prenatal sonography in many
instances shows the abnormal posterior fossa and cerebellum (“banana” sign) before the hydrocephaly is seen. The
second theory proposed by Cleland
130
is that of primary
dysgenesis of the hindbrain; this theory does not explain
the cranial and supratentorial anomalies that are commonly seen in patients with Chiari II malformation and
B
D
spina bifida, but it explains the posterior fossa anomalies.
The third theory suggests that the open and tethered spinal cord pulls the hindbrain posteriorly, resulting in the
vermian and brainstem herniation seen in Chiari II malformation. The fourth theory is the unified theory of McLone
and Knepper,
131
which includes aspects of all of the above
theories. In the unified theory, the Chiari II malformation
A
Figure 5–32. Transabominal songraphy at 29 weeks, 6 days. ( A) Parietal bone round defect ( arrows ), (B) Color Doppler of the abnormally large vein
( arrow ) reaching the parietal bone at the level of the defect. (Courtesy of Gustavo Malinger.)
B