Diagnostic ultrasound ( PDFDrive )

1480 PART IV Obstetric and Fetal Sonography
portion of the placenta. Circumvallate placentas can also be
confused with uterine synechiae (Fig. 43.23A), uterine septum
(Fig. 43.23B), and amniotic bands. Carefully identifying the
insertion of the membranes and determination of the echogenicity
of the rolled edge of placenta, which should be similar to that
of the placenta, should provide the correct diagnosis.
If a circumvallate placenta is identiied, even if it seems to
occupy only a small portion of the placenta, the rest of the placenta
must be evaluated to determine whether the rolled edge of
membranes involves the entire placenta. hree-dimensional
sonography has been suggested as helpful for diagnosing a
complete circumvallate placenta with the appearance of a “tire
mounted on a wheel” or the “tire sign.” 128 Complete circumvallate
placentae are associated with adverse neonatal outcomes, including
FIG. 43.21 Molar Pregnancy. Transvaginal sonogram in the late
irst trimester demonstrates a moderate amount of gestational tissue
with multiple cystic spaces.
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1
placental abruption, preterm delivery, oligohydramnios, IUGR,
emergency cesarean delivery, Apgar scores less than 7, and
perinatal death. 129,130 Fortunately, complete circumvallate placenta
is rare, whereas partial circumvallate placentas are quite common
and should be regarded as normal variants.
Evaluating second-trimester placental shelves to determine
whether the sonographic inding persisted into the third trimester,
Shen et al. 129 found an incidence of 11% for the identiication
of these shelves at the 13- to 16-week scan. Of note, none of the
placental shelves occupied more than 25% of the placenta. Also,
none of the partial circumvallate placentas could be sonographically
appreciated in the third trimester. All neonates had a normal
outcome. A recent large study of postdelivery placenta inspection
yielded a complete circumvallate placenta incidence of 1.8%,
none of which was detected antenatally.
Succenturiate Lobe
Succenturiate lobes, or accessory lobes, of the placenta can be
a single lobe or multiple lobes in addition to the main placental
lobe (Fig. 43.24). heir incidence is as high as 6%. 28 Given that
placental tissue is present in the accessory lobe, there must be
arterial and venous connections to the main portion of the
placenta. One concern involves a retained placental accessory
lobe ater delivery, if not expected from the antenatal sonogram.
Succenturiate lobes can also lie over the cervix as a variant of
placenta previa. 126 Even more important is the concern over the
location of the vascular connection between the main placenta
and the succenturiate lobe. If the vessels lie in proximity to the
cervix, a vasa previa may be present.
When a succenturiate lobe of the placenta is identiied, it is
imperative that the vascular connection between the succenturiate
lobe and placenta be identiied. his can be diicult at times
because of poor visualization, especially later in pregnancy, and
because the closest distance between succenturiate lobe and
placenta is not always the route taken by the vessels. At a
A
B
FIG. 43.22 Circumvallate Placenta. (A) Transabdominal sonogram in the early third trimester shows rolled edges of the placenta (arrows).
(B) Transabdominal sonogram in the second trimester shows a placental shelf (arrow), which has echogenicity similar to the remainder of the
placenta. See also Videos 43.12 and 43.13.