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190
Chapter 5 Anomalies of Dorsal Induction
rare prolonged cases of survival up to 14 months have been
reported.
59
Obstetric Management
Termination should be offered at the time of diagnosis,
given the fact that this is a lethal anomaly. For those fetuses
diagnosed at the time of delivery, compassionate and comforting care should be given. Most fetuses with anencephaly die within the first week of life; however, survival has
been reported.
60
INIENCEPHALY SEQUENCE
Synonyms
None
Definition
Iniencephaly is a complex and lethal malformation that
has three main features: a defect in the occiput involving
the foramen magnum, retroflexion of the entire spine that
forces the fetus to look upward with its occiput directed
toward the lumbar region, and open spinal defects of variable degree.
Incidence
Iniencephaly is a rare malformation. The reported incidence of iniencephaly ranges from 1 to 6 per 10,000 births.
Like anencephaly, most of the affected fetuses are female
(90%).
61 – 66
67
Associated Anomalies
Other malformations occur in up to 84% of fetuses with
iniencephaly. Many of these associated malformations can
only be diagnosed beyond the first trimester of the pregnancy. Among the associated anomalies, spina bifida is the
most common, occurring in up to 50% of cases.
70
Other
anomalies are anencephaly, hydrocephaly, microcephaly,
ventricular atresia, holoprosencephaly, polymicrogyria,
agenesis of the cerebellar vermis, occipital encephalocele,
cleft lip and palate, absence of the mandible, diaphragmatic hernia, thoracic cage deformities, cardiac malformation, urinary tract anomalies, omphalocele, clubfoot, and p
olyhydramnios.
62 , 63 , 66 , 69 , 71 , 72
Recurrence Risk
The recurrence risk of iniencephaly is 1.9%, which is similar to that quoted for most NTDs (see above).
Sonographic Diagnosis
Using TVS, iniencephaly has been diagnosed as early as
12.5 weeks’ gestation
the head appears large and held in retroflexion, the neck is
not visualized, and the spine is usually lordotic ( Figure 5–15 ).
In cases of iniencephalus apertus, a posterior cephalocele is
present in the occipital area ( Figure 5–16 ). On transverse
views, the open spinal defect is present. On axial sections,
the head circumference may be several standard deviations
below the mean, consistent with microcephaly. In addition,
a size/dates discrepancy in a well-dated pregnancy may be
the first sign of an iniencephalic fetus.
73
( Figure 5–14 ). On the median plane,
Pathogenesis
Iniencephaly, like anencephaly, results from a failure of
fusion in the cervical and upper thoracic region of the
upper spine. This lack of fusion secondarily results in a
short neck and trunk, cervical and upper thoracic vertebral
defects, defects of the thoracic cage, anterior spina bifida,
diaphragmatic defects, and hypoplasia of the lung and/
or heart.
68
The malformation results from developmental
arrest of the embryo no later than 24 days after conception.
This results in persistence of the embryonic cervical retroflexion that leads to failure of the neural groove to close
in the area of the cervical spine or the upper thorax.
61 , 62 , 69
This defect most likely occurs only a few days later than
anencephaly.
Iniencephaly has been divided into two types: iniencephalus clausus (or the closed type) and iniencephalus
apertus (or the open type). In the latter, an occipital
cephalocele protruding through the foramen magnum and
occipital bone defect is present
67
( Figures 5–14 , 5–15 , and
5–16 ).
Etiology
Iniencephaly, like all NTDs, has multifaceted causes,
mostly a mix of genetic and environmental factors. Folic
acid can decrease the recurrence rate.
Differential Diagnosis
The main differential diagnosis is the Klippel-Feil syndrome (KFS). In the typical clinical scenario, there is a
triad of findings consisting of a short neck, low posterior
hairline, and limited neck movement, although <50% of
patients demonstrate all three clinical features.
74
detected by prenatal sonography are cervical vertebral
anomalies, short neck, low-set ears, and facial asym-
75
Other conditions that should be considered are
metry.
Jarcho-Levin syndrome, Gorlin syndrome, anencephaly
with raschischis, and cervical encephalocele.
Prognosis
Iniencephaly, especially the open type, is essentially a lethal
anomaly, with most of the fetuses with this condition being
stillborn or dying shortly after birth. However, long-term
survival has been reported of up to 2 years of age.
Obstetric Management
Termination should be offered at the time of diagnosis,
given the fact that this is a lethal anomaly. For those fetuses
diagnosed at the time of delivery, compassionate and comforting care should be given. Dystocia of labor may occur
due to the abnormal head position.
Findings
72
Chapter 5 Anomalies of Dorsal Induction
Liv. Bowel
Liv.
AB
191
CD
Figure 5–14.
absence of the neck. Omphalocele was also present. L, liver. (B) The specimen from the side showing the shortened neck. (C) The dorsal view of the
specimen showing the total spinal rachischisis. (D) Sagittal view of the specimen.
Iniencephaly at 12½ postmenstrual weeks. (A) Sonographic appearance in the median plane. Note the short body length due to the
A
B
Figure 5–15. Iniencephaly at 19 postmenstual weeks. (A) The ultrasound image. Note the deviant brain structure and the extended head.
(B) Pathologic specimen.
192
Chapter 5 Anomalies of Dorsal Induction
H
A
C
Figure 5–16. A fetus with iniencephaly at 22 postmenstrual weeks. (A) Longitudinal median section. On the left of the picture, the outline of the head
(H); on the right, the distorted vertebral column with several kyphoscoliotic deformations. Note the bulging brain tissue (occipital meningomyelocele,
arrow ). (B) Transverse section with the open vertebral column (rachischisis) is seen with the bulging brain tissue ( arrow ). (C), (D) The aborted specimen
demonstrating the absence of a neck (iniencephaly) and rachischisis with meningomyelocele.
CEPHALOCELE
Synonyms
Cranium bifidum, encephalocele
B
D
Incidence
The reported incidence ranges from 1 per 3500 to 1 per
5000 live births.
approximately 10 times less common than encephalocele.
77
It is estimated that meningoceles are
Cephalocele may involve the occipital, frontal, temporal,
Definition
Cephaloceles are cranial defects, along bony sutures, in
which there is a herniation of the brain and/or meninges.
Sporadic or nonsyndromic cephaloceles account for ∼5%
of all NTDs.
tissue, it is termed an encephalocele; if only cerebrospinal
fluid is present (CSF), it is termed a meningocele.
76
When the cephalocele sac contains brain
and parietal regions of the fetal head ( Table 5–5 ). The
occurrence of the different types of cephaloceles shows
geographical variation. In Europe and North America,
66% to 89% of all cephaloceles are occipital, with the balance being equally distributed among frontal and parietal
cephaloceles. In Thailand and countries of southern Asia,
the frontal (sincipital) location is more common than the
occipital.
14 , 32 , 55 , 78 – 82
78
Chapter 5 Anomalies of Dorsal Induction
193
Table 5–5. CLASSIFICATION OF CEPHALOCELE
ACCORDING TO THE SITE OF THE
BONE DEFECT
Occipital
Anterior
Sincipital
Basal
Parietal
Modified, with permission, from Simpson DA, David DJ, White J.
Cephalocele: Treatment, outcome, and antenatal diagnosis. Neurosurgery .
1984;15:14–21.
Pathogenesis
Occipital cephaloceles occur more commonly in female
than in male fetuses, in contrast to parietal and sincipital
cephaloceles, which are more prevalent in males ( Figures
5–17 , 5–18 , 5–19 , 5–20 , 5–21 , 5–22 , and 5–23 ).
development of most severe cephaloceles takes place no
later than 26 days after conception, when the anterior
neural tube closes.
11
Anterior or sincipital cephaloceles are frontonasal
herniations of the brain and/or meninges through a skull
78
The
defect. Anterior cephaloceles always occur in the midline
sagittal axis of the cranium. Cephaloceles occur at the sites
of the fontanelles (frontal, sphenoidal) or at the cribriform plate of the ethmoid, the foramen cecum, the foramen magnum, or through a suture line.
54 , 81 , 83 , 84
They are
divided into two main types: sincipital and basal. Sincipital
cephaloceles are external lesions that occur near the root
of the nose (glabella) and are subdivided into nasofrontal,
nasoethmoidal, and nasorbital types ( Figures 5–24 , 5–25 ,
5–26 , 5–27 , and 5–28 ). Basal cephaloceles are internal
lesions that occur within the nose, pharynx, or orbit.
These are further subdivided into five types: sphenoorbital,
sphenomaxillary, transethmoidal, sphenoethmoidal, and
sphenopharyngeal.
83 , 85
The pathogenesis of anterior cephaloceles is unclear.
Anterior cephaloceles occur early in development at around
45 to 50 days of embryonic age. This is the time when the
base of the occiput and the sphenoid body develop and
assume their normal appearance.
86
Anterior cephaloceles,
like occipital cephaloceles, may occur as a sporadic defect,
associated with a chromosomal syndrome, or as part of a
nonchromosomal developmental syndrome. Syndromes
that include an anterior cephalocele are aberrant tissue band
syndrome, frontonasal dysplasia, absent corpus callosum,
clefting, craniostenosis, hypothalamic pituitary dysfunction,
meningocele, and Roberts-SC phocomelia syndrome.
85 , 87 , 88
Parietal cephaloceles are located in the midline
between the lambda and the bregma. The size, shape,
A B
Figure 5–17. Posterior encephalocele at 12 weeks, 6 days. (A) Series of parallel sagittal sections as viewed using the tomographic imaging display
showing the brain tissue extending into the amniotic sac ( arrow ). (B) Picture generated using surface rendering showing the head with the posterior
encephalocele from a lateral view.
194
Figure 5–18. Using transabdominal sonography, a large posterior encephalocele is seen in this fetus at 19 postmenstrual weeks. (A) An axial section
displays the large cephalocele sac. Brain tissue is seen extending into the sac. (B) Sagittal section displays the encephalocele. (C) A 3D reconstruction of
the posterior encephalocele.
Chapter 5 Anomalies of Dorsal Induction
ABC
position, and content of the cephalocele sac may be
variable.
78
The cephalocele sac may contain the parietal
cortex.
Atretic meningoceles are extremely infrequent, affecting the parietal and positioned close to the lambda suture.
Usually there is a round bone defect that contains meninges
and neural rests.
topia, cerebellar dysgenesis, and venous anomalies, have
been reported.
A
89
Associated anomalies, including hetero-
90 , 91
Etiology
Cephaloceles usually occur as an isolated lesion, but in
a small percentage of cases, they may be part of a nonchromosomal or chromosomal syndrome. Chromosomal
abnormalities associated with cephaloceles are trisomy 13; trisomy 18; mosaic trisomy 20; deletion (13q),
(2)(q21→q24); monosomy X; duplication (6)(q21→qter),
(7)(pter→p11), and (8)(q23→qter). We have encountered
B
B
Figure 5–19.
rior aspect of the sagittal suture is seen using 3D transvaginal sonography
in a patient at 21 weeks, 4 days, referred to our unit for evaluation of
borderline ventriculomegaly. (A) The volume is displayed using the three
orthogonal planes (Box A: sagittal; Box B: coronal; Box C: axial) the rendered imaged is seen in the lower right box. (B), (C) Volume displayed
using tomographic imaging. In B the image is zoomed, and the small cra-
nial defect ( arrow ) is seen in serial sagittal sections; in C in serial coronal
sections. The herniated brain, B, is seen within the cephalocele sac.
A small posterior encephalocele arising from the poste-
B
C
Chapter 5 Anomalies of Dorsal Induction
AB C
Figure 5–20. Parietal cephalocele at 22 postmenstrual weeks. (A) The small (7 mm) bony defect lies between the small white arrows. Note that this
is evident in the oblique–1 sections. The brain tissue on all sections appeared normal. (B) A slightly more lateral section shows the posterior horn with
a hyperechogenic choroid plexus and the skull defect with the sonolucent meningocele. The picture in the inlay was taken across the plain marked by
the white line. The size of the lesion was 2.4 × 1.1 cm. (C) Posterior views of the lesion. The patient refused further testing and requested termination
of the pregnancy.
195
two fetuses with large posterior encephalocele and a deletion of the short arm of chromosome 13 (13q) (see Figure
5–23 ). Besides the encephaloceles, these fetuses have skeletal malformations. The most remarkable malformation is
the absence of the thumb.
Some of the nonchromosomal syndromes that feature
a cephalocele are listed in Table 5–6 . In these cases, the
karyotype is normal, and the clues to the prenatal diagnosis
are the sonographic findings. Therefore, it is imperative to
perform a detailed targeted scan looking for other sonographic abnormalities. This is especially important if this is
the first affected fetus.
Associated Anomalies
In a recent study 65.6% of the fetuses/infants with cephaloceles had at least one major malformation, and 34.4%
had an isolated cephalocele.
26-year experience with nonsyndromic cephaloceles. In
their series the extracranial malformations associated with
cephaloceles were cardiovascular (VSD, coartaction of the
aorta, single umbilical artery), urogenital tract (pyelectasis,
ureteral agenesis), malformations of the extremities (talipes equinovarus), and malformations of the thorax and
abdominal wall (gastroschisis, diaphragmatic hernia, costal
malformations).
Of the syndromic causes of cephaloceles, MeckelGruber, Walker-Warburg and Knobloch syndromes are
among the most common ( Figures 5–29 , 5–30 , and 5–31 ).
Meckel-Gruber syndrome is lethal. There are several types
of Meckel-Gruber syndrome, of which type 1 is caused by
mutation in a gene encoding a component of the flagellar
apparatus basal body proteome ( MKS1; 609883; gene map
92
Joo et al
76
published their
locus 17q23). Approximately 80% of the cases of MeckelGruber syndrome have an occipital cephalocele. The two
other consistent findings in the typical triad of malformations are bilateral renal cystic dysplasia and postaxial polydactyly of both hands and feet (see Figure 5–30 ).
latter malformations have been reported to be present in
95% and 75% of cases.
93
In order to make the diagnosis
78 , 82
These
of Meckel-Gruber syndrome, at least two of the three
major signs must be present. Using sonography, the
diagnosis can be made by the early second trimester of
pregnancy.
94
However, in patients with a prior history of
Meckel-Gruber syndrome, the diagnosis could be made in
the first trimester (see Figure 5–29 ). The cystic dysplastic
kidney is the most consistent anomaly. The kidneys are up
to 10 to 20 times larger than normal, are hyperechogenic,
and contain multiple small cysts measuring between 2 and
82 , 95
5 mm.
As a result of the dysplastic kidneys, there is
impaired renal function, and oligohydramnios is present.
In addition, the fetal bladder is not imaged by US. The
size of the cephalocele may be variable. In one of our cases
of Meckel-Gruber syndrome, the skull defect measured
2 mm (see Figure 5–30 ). Other sonographic findings are
microcephaly with a biparietal diameter (BPD) and head
circumference lagging behind dates and hydrocephaly.
Associated malformations that may present in MeckelGruber syndrome include renal agenesis, renal hypoplasia,
ureteral duplication, cleft lip and palate, micrognathia,
microphthalmia, ambiguous genitalia, congenital hepatic
fibrosis, talipes equinovarus, short limb dwarfism, malformed tongue, intestinal malrotation, Dandy-Walker malformation, and congenital heart defects.
defects include VSDr or ASD, aortic hypoplasia or coarctation, aortic valvular stenosis, and rotational anomalies.
96 , 97
The heart
82
196
Chapter 5 Anomalies of Dorsal Induction
A
C
E
24 w
B
D
F
G
Figure 5–21. Occipital encephalocele. The patient presented at 24 postmenstrual weeks for dating US. The measurements revealed microcephaly and
the occipital bulging structure. (A) Median section of the brain showing the bony lesion between the two white arrowheads. Note the typical shape of the
corpus callosum ( small arrows ) and the small cavum septi pellucidi. (B) This view concentrates on the posterior herniated sac marked by an open arrow;
a very small echogenic structure is bulging into the fluid. (C) Midcoronal–1 section: almost no anterior horns are seen on this section. (D) Midcoronal–3
section: very small lateral ventricles with echogenic choroid plexus is seen. (E), (F) Targeted views of the posterior cephalocele marked by open arrows
inside a small (½ cm) echogenic tissue; this may correspond to meninges or a very minute amount of brain tissue. (G) The specimen showing the translucent thin membrane of the cephalocele bulging through the midline skull defect. In addition, this fetus had single umbilical artery, dilated renal pelves,
cardiomegaly with pericardial infusion, and an interventricular septal defect with a wide pulmonary artery.
Chapter 5 Anomalies of Dorsal Induction
197
A
C
D
B
E
25w
F
Figure 5–22.
(A), (B) Median views showing the skull defect between the two white arrows and the bulging brain and cerebrospinal fluid bulging into the sac.
(C), (D) Frontal–1 and –2 views, showing what appears to be normal symmetrical brain tissue. Panel (D) shows the anterior horns ( small arrows ).
(E) A horizontal section of the defect and the herniated mass. The head demonstrated severe microcephaly for the age. (F) The specimen demonstrating
severe microcephaly and the large posterior encephalocele. The chromosomal studies demonstrated a 13q deletion.
Sonographic pictures of an occipital encephalocele at 25 postmenstrual weeks. Delivery took place at 34½ postmenstrual weeks.
198
Chapter 5 Anomalies of Dorsal Induction
AB
C
E
D
F
G
Figure 5–23.
age. Microcephaly was also diagnosed (the biparietal diameter [BPD] and the head circumference were consistent with 26 postmenstrual weeks).
(A) Frontal–2 section showing the longitudinal sulcus and apparently normal brain tissue. (B) Median section depicting the large bony defect in
the occipital region marked by two black arrowheads. Brain tissue seems to protrude, pulling with it the posterior horn and the choroid plexus.
(C), (D) Different sections of the encephalocele itself. (E), (F) Coronal sections by definition, showing the longitudinal sulcus and the dilated occipital
horns and within it the choroid plexus. (G) A picture of the neonatal head showing the large occipital encephalocele. Clinical course: The neonate was
found to have a chromosome 13q deletion and was admitted and discharged several times but reached the age of 1½ years. Another anomaly included
absence of the thumbs. Cranioplasty was performed, which was complicated by wound infection and worsening hydrocephaly. A drain was placed; however, the infant was admitted several times to the hospital because of cerebrospinal fluid leak from the incision site. The infant had severe mental retardation and seizure disorder. The computed tomography (CT) studies showed that the encephalocele included the cerebellar hemispheres and a portion of
the posterior horns (as diagnosed by the US pictures), in addition, partial agenesis of the corpus callosum with the splenium virtually absent was seen.
Occipital encephalocele in a fetus at 34 postmenstrual weeks. This patient presented for her first US exam at this gestational
Chapter 5 Anomalies of Dorsal Induction
199
A
C
E
B
D
F
G
H
J
I
Figure 5–24. Anterior encephalocele at 13½ postmenstrual weeks. (A) Median section showing the eye, nose, upper and lower lips, and a lobulated
mass protruding between the lips. (B), (C) Slightly and progressively lateral paramedian sections showing not only the lesion but also a sizable
sonolucency in the skull probably left behind by the protruding mass, leaving that space vacant. (D) Horizontal section of the lesion showing the
protruding mass between the two orbits. (E)–(H) Horizontal paramedian and median sections of the lesion. These pictures where aimed at determining
the place of the sonolucency in the skull. This was finally located to be in the area of the anterior horn almost symmetrically between the two hemispheres
( arrowheads ). (I) The side view of the aborted specimen showing the bulging cephalocele emerging through the mouth. (J) A median transection of
the head demonstrating the origin of the lesion protruding from the anterior horn. The sonolucent space in the area of the frontal horn detected by US
is now clearly seen on this section ( black arrow ). (A–G from Monteagudo A, Timor-Tritsch IE, Cephalocele, Anterior. www.thefetus.net, (1992) with
permission.)