Diagnostic ultrasound ( PDFDrive )

1238 PART IV Obstetric and Fetal Sonography
F
A B C
T
FIG. 35.21 Sirenomelia. (A) Sagittal view of fetus at 12 weeks’ gestation shows unusual angulation of lower extremity. (B) Long-axis view
of a single lower extremity. (C) In a different fetus, radiograph shows single femur (F) and single tibia (T). Note the segmented defects in the
vertebrae of the thoracic and lumbar spine (arrows).
gastrointestinal, and cardiac systems are common. Occurrence
is sporadic; caudal regression is more common in infants of
mothers with diabetes mellitus. he cause has not been established.
Sonography can demonstrate absence of the sacrum and shortened
femurs. he legs can be lexed and abducted at the hips, and
there may be clubfoot. Sonography may detect associated urinary
anomalies (renal agenesis, cystic dysplasia, caliectasis) and
gastrointestinal abnormalities (e.g., duodenal atresia). 114 he
prognosis depends on the severity and extent of the skeletal
abnormalities and associated anomalies. In sacral agenesis with
no internal organ involvement, there are usually deicits in the
legs and deicient control of bladder and bowel functions. In
infants with internal organ involvement, the prognosis is related
to these defects.
SIRENOMELIA
Sirenomelia sequence is a rare disorder in which the legs are
fused and the feet are deformed or absent 115 (Fig. 35.21). he
cause is probably an aberrant fetal artery that branches from
the upper abdominal aorta and passes into the umbilical cord
to the placenta. 116 Arterial blood low bypasses the lower fetal
body. he distal abdominal aorta, the aorta’s distal branches,
and subtended structures are small and underdeveloped. his
leads to malformations of spine, legs, kidneys, gut, and genitalia.
Normally the umbilical arteries, which arise from the fetal iliac
arteries, carry blood from the fetus into the umbilical cord and
then into the placenta.
At sonography, there is advanced oligohydramnios because
of reduced or absent renal function. he legs are fused, or there
is a single leg. he feet are absent, or there may be a single foot.
here may be sacral agenesis, deiciency of the lower lumbar
spine, and thoracic anomalies. hese indings may be diicult
to appreciate because of the advanced oligohydramnios or
anhydramnios. 112 he prolonged anhydramnios causes pulmonary
hypoplasia, which is usually fatal. he risk of recurrence is the
same as in the general population.
SACROCOCCYGEAL TERATOMA
Fetal teratomas may arise from the sacrum or coccyx, from other
midline structures from the level of the brain to the coccyx, or
from the gonads. 117 Sacrococcygeal teratomas arise from the
pluripotent cells of Hensen node located anterior to the coccyx.
Sacrococcygeal teratomas contain all three germ layers (ectoderm,
mesoderm, and endoderm) and thus may contain elements of
many tissues, including neural, respiratory, and gastrointestinal.
Sacrococcygeal tumor is rare (1 : 35,000 births) 118 but is the most
common tumor among neonates. Females are afected four times
more frequently than males. Sacrococcygeal teratomas are classiied
into four types 118 : type I, tumor predominantly external
with only minimal presacral involvement; type II, tumor presenting
externally but with signiicant intrapelvic extension; type
III, tumor apparent externally but with predominant pelvic mass
and extension into the abdomen; type IV, tumor presacral with
no external presentation (Fig. 35.22). 117
Types of Sacrococcygeal Teratomas
Type I (47%): external mass predominant
Type II (34%): external mass with signiicant internal
component
Type III (9%): internal mass predominant, with smaller
external component
Type IV (10%): presacral mass only
At birth, 75% of sacrococcygeal teratomas are benign, 12%
are immature, and 13% are malignant. Because malignant potential
increases with the age of the infant, surgery must be performed
shortly ater birth.
Sonography usually demonstrates a mass in the rump or
buttocks area adjacent to the spine 119 (Video 35.6). Most teratomas
(85%) are either solid or mixed (solid and cystic); 15% are mostly
cystic, which is a benign sign. Calciications are frequently present.