Diagnostic ultrasound ( PDFDrive )

1404 PART IV Obstetric and Fetal Sonography
A
B
C
FIG. 40.33 Sirenomelia. (A) Cross section of lower extremities. Femurs (arrows) are closer than expected because of fusion of the overlying
soft tissues with a continuous layer of overlying skin (arrowheads). (B) Sacral agenesis with abrupt termination of the lower spine (arrow). (C)
Single, fused lower extremity and sacral agenesis.
Extremity enlargement may also be related to thickened subcutaneous
tissues, as in hydrops or large-for-gestational-age infants.
Kyphoscoliosis may be a manifestation of an isolated vertebral
defect or may be associated with myelomeningocele or with
complex syndromes, such as VACTERL, limb–body wall
complex, neuroibromatosis, arthrogryposis, diastrophic
dysplasia, and other skeletal dysplasias.
HAND AND FOOT MALFORMATIONS
A complete digit evaluation can be performed by 12 to 13 weeks’
gestation. 105 he fetus typically maintains open hands with digit
extension in the irst half of gestation, whereas in the second
half of gestation the fetus may maintain hand closure for relatively
prolonged periods, up to 30 minutes, limiting detailed evaluation.
he incidence of inger abnormalities is approximately 1 in 1000
fetuses, of which 60% will have either an associated malformation
sequence or karyotypic malformation. he optimal time for
evaluation of the hands and feet is during the second
trimester. 14,106-108
Transient indings represent a potential pitfall in the analysis
of the distal extremities. During the second half of gestation,
the fetus may appear to have pseudosyndactyly by maintaining
a closed hand for prolonged periods. he diagnosis of an isolated
clubfoot can be risky because the fetus can hold the foot in a
position to suggest the diagnosis in the absence of a structural
defect. An apparent clubfoot may be secondary to positioning
against the maternal uterine wall or in the setting of oligohydramnios,
which subsequently resolves with a change in fetal
position or amniotic luid volume.
Aneuploidy is associated with an increased risk of hand and
foot anomalies, including persistent clenched hand, overlapping
digits, clinodactyly, polydactyly, syndactyly, simian creases,
talipes equinovarus, rocker-bottom foot, and sandal toes (Fig.
40.36).
Persistent clenched hand with overlapping of digits occurs
in more than 50% of trisomy 18 fetuses and is generally bilateral.
his characteristic hand appearance is highly suggestive of trisomy
18 but can also occur in other conditions, such as fetal akinesia
syndrome and triploidy.
Clinodactyly is the permanent incurvature of a inger.
Clinodactyly, caused by asymmetrical hypoplasia of the middle
phalanx (medial shorter than lateral aspect), most oten involves
the ith inger and is associated with trisomies 13, 15, 18, and
21 (Fig. 40.36G). Clinodactyly occurs in 60% of fetuses with
trisomy 21; however, up to 18% of normal fetuses may have a