Diagnostic ultrasound ( PDFDrive )

CHAPTER 43 Sonographic Evaluation of the Placenta 1471
otherwise indicated) are serious complications of pregnancy
associated with maternal blood loss, need for hysterectomy, and
retained products of conception. With ultrasound, placenta accreta
can be identiied antenatally so that delivery plans can be made
prospectively, improving the outcome for mother and child.
Although placenta accreta (or increta or percreta) can occur
in any pregnancy, important risk factors include prior uterine
surgery (with risk increasing with increasing number of prior
cesarean deliveries), placenta previa, unexplained elevated
maternal serum alpha-fetoprotein (MS-AFP), increased maternal
cell-free placental lactogen, and advancing maternal age. 67-70 A
woman with no placenta previa and no prior history of cesarean
section has a baseline risk of 0.26% for placenta accreta. his
increases almost linearly with number of prior cesarean sections,
to 10% in patients with four or more. 71 Women with a placenta
previa and an unscarred uterus have a 5% risk of clinical placenta
accreta. With a placenta previa and one previous cesarean section,
the risk of placenta accreta is 24%; this risk increases to 67%
with a placenta previa and four or more cesarean deliveries. 71
Several sonographic signs are associated with placenta accreta.
he presence of a coexisting placenta previa in the majority of
cases makes it particularly likely that the adherent portion of
the placenta will be low in the uterus, in the region of a prior
cesarean scar. his simple fact makes the evaluation of these
placentas much more straightforward with TVS. Sonographic
indings of placenta accreta include loss of the normal hypoechoic
retroplacental-myometrial interface, thinning or disruption of
the hyperechoic subvesicular uterine myometrium/serosa, presence
of focal exophytic masses, and numerous placental lakes 72-75
(Fig. 43.8, Video 43.3).
he color Doppler ultrasound indings suggestive of placenta
previa accreta include difuse lacunar blood low throughout
the placenta, dilated vascular channels between the placenta and
bladder or cervix, absence of the normal subplacental venous
low, and the demonstration of vessels crossing the placentalmyometrial
disruption site. 76,77 hree-dimensional sonography
may also be helpful for evaluation of vascular anatomy in the
setting of a placenta accreta. 78,79 he gray-scale and color Doppler
sonographic indings described for placenta accreta are also
present, but more exaggerated, in placenta increta and placenta
percreta (Figs. 43.8 and 43.9; Videos 43.4 and 43.5). hreedimensional
color and power Doppler ultrasound are helpful to
demonstrate the extensive torturous vascularity seen with such
placentas. Greatly increased vascular lacunae with turbulent or
“tornado” blood low increases the likelihood of placenta increta
or placenta percreta. 80
Many recent studies have documented the use of ultrasound
indings to identify women with placenta accreta. A recent
meta-analysis documented that incorporation of sonographic
abnormalities (placental lacunae, loss of the placental-myometrial
hypoechoic space, abnormalities of the uterine-bladder interface,
and color Doppler) led to a sensitivity of 91% and speciicity of
97% for the detection of placenta accreta. 81 A “Placenta Accreta
Index” was reported that included number of prior cesarean
deliveries, placental location, presence and grade of lacunae,
smallest myometrial thickness, and presence of bridging vessels,
and constructed a receiver operating characteristic curve whereby
the area under the curve was 0.87 (95% conidence interval [CI],
0.8, 0.95). A score of 0 to 9 had a range of probability of placenta
accreta from 2% to 96%, respectively. 82 Further work is necessary
to determine the historical and sonographic parameters needed
to optimize prenatal diagnosis.
As in many aspects of obstetric sonography, early diagnosis
is preferable. In women with a history of cesarean delivery, a
gestational sac in the lower half of the uterus, at or before 10
weeks’ gestation, is associated with placenta accreta, 83 as are
irst-trimester placental lacunae, an irregular placental-myometrial
interface and placenta previa 84-86 (Fig. 43.10). Cesarean scar ectopic
pregnancies appear to be precursors of placenta accreta. 87 When
the diagnosis is unclear or nonspeciic indings are present,
magnetic resonance imaging (MRI) may be helpful, 88-93 particularly
when the placenta is posterior over an area of prior uterine scar,
such as from myomectomy (Fig. 43.11).
Information about placenta accreta and its variants is indispensable
for delivery management. Accurate prenatal diagnosis
allows uterine conservation and avoidance of massive blood loss
at delivery. Strategies include preoperative placement of internal
iliac artery balloon catheters and ultrasound-guided fundal
classical cesarean incisions to deliver the fetus above the upper
margin of the placenta.
PLACENTAL ABRUPTION
Placental abruption is one of the worrisome causes of vaginal
bleeding in the latter part of pregnancy because it contributes
to perinatal mortality. Patients typically present with thirdtrimester
vaginal bleeding associated with abdominal or uterine
pain and labor. he incidence is approximately 0.5% of pregnancies.
History of prior abruption, hypertension, prolonged rupture
of membranes, IUGR, chorioamnionitis, polyhydramnios,
maternal thrombophilias, maternal substance use (tobacco,
alcohol, cocaine), maternal trauma, and advanced maternal age
are all risk factors for placental abruption. 94-96 he diagnosis of
placental abruption is typically made based on clinical indings;
the retroplacental clot is frequently isoechoic to the placenta or
myometrium and cannot always be identiied sonographically.
A subplacental hematoma between the placenta and uterine
wall is a placental abruption (Fig. 43.12, Videos 43.6 and 43.7).
his should be diferentiated from a subchorionic hematoma,
in which the hematoma is located beneath the chorion, not the
placenta. Although a subchorionic hematoma can occur anytime
during pregnancy, it is more common in the irst half of pregnancy,
and its appearance will change as the hematoma organizes (Fig.
43.13A). A preplacental hematoma is a rare condition likely
caused by bleeding from fetal vessels and located on the fetal
surface of the placenta under the chorion (Fig. 43.14, Videos
43.8 and 43.9). Because preplacental hematomas likely result
from the accumulation of fetal blood, prognosis may be poorer. 97
When massive, these hematomas are sometimes termed Breus
mole. Preplacental hematomas are associated with maternal
hypertension. 98
An acute hematoma has an echogenicity similar to that of
the placenta, making sonographic visualization diicult. As the
hematoma organizes, it becomes more hypoechoic (Fig. 43.13B)