Diagnostic ultrasound ( PDFDrive )

1182 PART IV Obstetric and Fetal Sonography
TABLE 34.2 Features of Some
Autosomal Recessive Syndromes Associated
With Encephalocele a
Meckel-Gruber
Walker-Warburg
Joubert and
related
Hydrolethalus
Fraser
Robert
Cystic renal dysplasia, polydactyly,
other central nervous system
abnormalities, microphthalmia, cleft
lip and palate, micrognathia,
ciliopathy
Hydrocephalus, agyria (lissencephaly
type 2), retinal dysplasia, vermis
hypoplasia, kinked brainstem,
muscular dystrophy
Vermian hypoplasia, deep
interpeduncular fossa (molar tooth),
hydrocephalus, ciliopathy
Hydrocephalus, cerebral abnormality,
polyhydramnios, micrognathia,
polydactyly, heart defects
Cryptophthalmos, syndactyly, genital
abnormality, renal abnormality,
laryngeal stenosis
Phocomelia (pseudo-thalidomide), cleft
lip and palate, intrauterine growth
restriction
a Note that all have many other additional indings. 109
he prognosis of cephaloceles depends on the location of the
lesion, the amount of herniated brain, the formation of the
underlying brain, associated anomalies, and genetic abnormalities.
Prenatal and perinatal mortality rates are high, and intellectual
impairment is common. If discovered before viability, pregnancy
termination is considered. Later in pregnancy, management
depends on the size and location of the encephalocele and
associated anomalies. 102,112,113
Ciliopathies
Ciliopathies are a group of disorders resulting from abnormal
structure or function of cell surface cilia due to mutations in
ciliary genes. Cilia are found on the surface of almost all cells
of vertebrates, and their functions are very much more complex
than providing simple transport as seen in bronchi and various
anatomic ducts. Normally functioning cilia are required for the
normal development and function of seemingly unrelated sites
including brain, kidneys, eyes, liver, and skeleton. In the brain,
cell surface cilia are involved with brain patterning and neuronal
migration and help direct CSF low. Abnormal ciliary function
may result in HC and other cerebral malformations including
encephaloceles. 114 Over 40 mutations of ciliary genes have been
found, resulting in over 1000 polypeptide abnormalities. As result,
the expression of ciliary gene mutation is variable. A single gene
mutation may cause diferent phenotypes, and mutations of
diferent genes may result in the same phenotype. Commonly
encountered ciliopathies have overlapping features such as
encephaloceles and include Meckel-Gruber syndrome, Joubert
syndrome, orofaciodigital syndrome, Bardet-Biedl syndrome,
autosomal recessive polycystic kidneys, autosomal dominant
polycystic kidneys, Jeune asphyxiating thoracic dystrophy,
Ellis-van Creveld syndrome, and others. 115
Joubert Syndrome
Joubert syndrome and related disorders (JSRD) have the key
feature of molar tooth sign visible on MRI. he molar tooth
appearance results from hypoplasia of the cerebellar vermis,
horizontal thick elongated cerebral peduncles, and deep interpeduncular
fossa at upper pons; on axial MRI of the brainstem,
these features look like a molar tooth. his sign is used as the
diagnostic test in children. JSRD is clinically characterized by
hypotonia, ataxia, psychomotor delay, irregular breathing, and
abnormal eye movements and has an incidence of about 1 per
80,000 pregnancies. Diferent combinations of ciliary gene mutations
can result in primary Joubert syndrome, and related disorders
have variable abnormalities of the neurons, eye, renal tubules,
and bile ducts and polydactyly. 116
On ultrasound the molar tooth sign indings of vermian
hypoplasia, thickened cerebral peduncles, and interpeduncular
notch may be visible by 20 weeks and conirmed by MRI if
needed. 117 Additional cerebral imaging indings can include
abnormalities of the corpus callosum and neuronal migrational
abnormalities, Dandy-Walker malformation (DWM), and
encephalocele as well as abnormalities in somatic structures. If
the mutation is known (about 50%), early diagnosis is possible
with chorionic villus sampling (CVS).
Prognosis is generally poor and related to extent of breathing
and feeding problems in the short term and renal and hepatic
complications in the long term.
Meckel-Gruber Syndrome
Meckel-Gruber syndrome is likely the most common syndromic
abnormality of the CNS and is characterized by occipital
encephalocele, enlarged dysplastic kidneys, hepatic duct proliferation,
polydactyly, posterior fossa abnormalities, and craniofacial
and heart defects and has features that overlap with JSRS.
Incidence is 1 per 13,000 to 140,000 live births. It is a lethal
autosomal recessive disorder associated with mutations in several
ciliary genes. he detection of its classic triad of large echogenic
kidneys, encephalocele, and postaxial polydactyly can allow
diagnosis as early as 14 weeks, but oligohydramnios in later
pregnancy may hinder detection of some of these features.
Autosomal recessive polycystic disease and trisomy 13 should
be considered in the diferential diagnosis. Genetic testing may
be possible in at-risk families. 118
Amniotic Band Sequence/Limb–Body
Wall Complex
Amniotic band sequence/limb–body wall complex describes
a variable collection of disruptive abnormalities and is associated
with adherence of the fetus to bands in the amnion.
Cases are sporadic, occurring in about 1 to 10 per 10,000
pregnancies, and typically have normal karyotype. Fetuses with
these conditions have a very variable range of complex, generally