Diagnostic ultrasound ( PDFDrive )

CHAPTER 39 The Fetal Urogenital Tract 1351
A
B
C
D E F
FIG. 39.19 Meckel-Gruber Syndrome. (A)-(C) Ultrasound images of a 14-week fetus show classic features of Meckel-Gruber syndrome: an
occipital encephalocele (thick arrow), large kidneys (only one shown [calipers]) with a mottled cystic appearance, and postaxial polydactyly (thin
arrow). (D)-(F) Postmortem photographs of the fetus (at 18 weeks’ gestation) demonstrate occipital encephalocele, large kidneys, and postaxial
polydactyly.
new dominant mutation and gene deletion. he severity of the
renal disease can be extremely variable (from prenatal oligohydramnios
or anhydramnios to normal renal function in adulthood)
and is not correlated with the genotype. 79
Meckel syndrome, also known as Meckel-Gruber syndrome,
is a lethal autosomal recessive ciliopathy that carries a 25% risk
of recurrence. It can be detected by sonography at 11 to 14 weeks’
gestation, particularly in families with prior afected pregnancies. 101
Sonographic diagnosis requires identiication of at least two
features of the classic triad: enlarged echogenic, cystic kidneys
(present in almost 100% of cases); occipital encephalocele
(60%-85%); and postaxial polydactyly (55%) 102 (Fig. 39.19).
During second-trimester sonography, it can be diicult to detect
the encephalocele and polydactyly because of oligohydramnios.
Microcephaly can be a useful clue to the presence of an encephalocele.
he kidneys are markedly enlarged (+4 SD), with a mottled
cystic appearance of the medulla surrounded by the hyperechoic
cortex. 103 Numerous small cysts are present, most smaller than
5 mm. he diagnosis of Meckel syndrome is particularly important
for counseling regarding the recurrence risk and possible prenatal
and preimplantation genetic diagnosis in future pregnancies.
Meckel syndrome can be caused by mutations in 1 of at least 13
genes. he proteins coded by these genes are known to have a
major role in cilia formation.
Hyperechogenic Kidneys
Fetal kidneys are considered hyperechogenic or “bright” when
they appear more echogenic than expected, compared with the
adjacent liver or spleen (Fig. 39.20). 67 Hyperechogenic kidneys
seen on prenatal ultrasound represent a diagnostic and prognostic
dilemma, particularly in the presence of normal AFV. here is
a wide diferential diagnosis, including genetically inherited renal
diseases (ARPKD, ADPKD, HNF1β mutations, Bardet-Biedl
syndrome, Perlman syndrome, Simpson-Golabi-Behmel),
obstructive dysplasia, aneuploidy, infections (especially cytomegalovirus),
nephroblastomatosis, renal vein thrombosis,
toxic injury, ischemia, and in some cases normal variant. 104
he proposed algorithm is useful for the evaluation of
hyperechogenic kidneys (Fig. 39.21). If there is sonographic
evidence of UT obstruction, renal dysplasia is a possibility,
especially when the kidneys are small or normal in size and
there are peripheral cortical cysts. 85 When extrarenal malformations
are detected, assessment of karyotype is indicated to exclude
aneuploidy (especially trisomy 13). If the kidneys and the
biometric measurements are above the 95th percentile, an
overgrowth syndrome (Perlman syndrome, Simpson-Golabi-
Behmel syndrome) should be considered. In both conditions,
there is generalized organomegaly and the AFV may be increased.
In Perlman syndrome there may be micrognathia and depressed
nasal bridge. In Simpson-Golabi-Behmel syndrome, there may
be congenital diaphragmatic hernia, clet lip or palate, and
polydactyly. In Bardet-Biedl syndrome, in addition to enlarged
hyperechogenic kidneys, postaxial polydactyly can be detected.
In several prospective and retrospective series of prenatally
diagnosed, isolated, bilaterally enlarged hyperechogenic kidneys,
the most common underlying diagnosis was ARPKD, followed