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Introduction: Placenta Accreta Spectrum

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One serious complication that may occur

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in the context of pregnancy is abnormal

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placentation or placenta accreta spectrum.

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Placenta accreta spectrum is a spectrum

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of abnormal relationships between

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the chorionic villi of the placenta

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and the uterine muscle or myometrium.

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Patients at risk for placenta accreta

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spectrum are patients who have had any

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type of trauma to the uterus that would

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interrupt or scar the uterine decidua.

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The decidua is an important structure

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in determining how far the chorionic

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villi of the placenta will travel

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when the placenta is developing.

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And there are chemical signals within the

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decidua that provide feedback to the placental

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cells to tell them when to stop migrating.

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So an absent or abnormal decidual layer

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will place the patient at increased

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risk of abnormal placentation.

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These risk factors include prior cesarean

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section, prior dilation and curettage

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of the uterus, and assisted reproductive

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technologies, including in vitro fertilization.

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Advanced maternal age and multiparity are

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also considered risk factors for placenta

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accreta spectrum, largely because patients who

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are older may have had prior pregnancies and

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because multiparity also places patients at

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greater risk for having a cesarean section.

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Within the spectrum of placenta accreta,

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we can further classify this condition

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into three different categories.

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Placenta accreta is an abnormal attachment

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of the placenta to the uterine decidua

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with abutment of the uterine myometrium.

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Placenta percreta is invasion of

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the placenta into the muscular

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layer of the uterus, the myometrium.

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And then placenta percreta is extension

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of placental tissue to or beyond

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the level of the uterine serosa,

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with the potential to invade structures in the

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pelvis adjacent to the site of uterine breach.

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A handy mnemonic that I like to use to remember

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these three classifications is that accreta

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is attachment, so abnormal attachment of

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the placenta to the decidua and myometrium.

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Increta is invasion of the myometrium by

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the placenta, and percreta is perforation of

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the uterine serosa by the placental tissue.

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Many patients with placenta

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accreta spectrum

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will also have placenta previa, which is

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a low-lying placenta that partially or

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completely covers the internal cervical os.

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We can see in this diagram that this patient

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indeed has a diagnosis of previa, with the

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placenta covering the internal cervical os.

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This patient also has placenta percreta, with

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a focal placental bulge extending outside

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of the uterus and toward the bladder dome.

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The reason that many patients with PAS

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will also have placenta previa is because

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that scarring that can act as an abnormal

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point of attachment for the placenta often

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occurs at the site of a prior cesarean

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section scar, which is intrinsically

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in the low uterine segment anteriorly.

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So that scarring will often lead to tethering

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of the uterus and a concomitant placenta previa.

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Identifying placenta accreta spectrum is

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critical to caring for this patient population.

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Because placenta accreta spectrum significantly

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increases the risk of peripartum hemorrhage.

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This is because when the placental cells

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move into the uterus during normal placental

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migration, they are remodeling and enlarging

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maternal blood vessels, including arteries.

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And so, in addition to the large volume of

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maternal blood that's circulating in the

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context of pregnancy, the placenta is also

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carrying a significant volume of blood.

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In patients with placenta accreta spectrum,

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we can also see aberrant vasculature.

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And so these patients are at significant

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risk of bleeding in the peripartum period.

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Because patients with placenta accreta

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spectrum undergo planned cesarean delivery,

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typically at 30 to 34 weeks gestation,

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there is also a significant risk of both

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maternal and fetal morbidity and mortality

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because of that premature delivery.

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And then finally, patients with placenta

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accreta spectrum are at increased risk of

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infection if the placenta is incompletely

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removed at the time of delivery.

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Management of placenta accreta spectrum

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is largely surgical, and goals of

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care for these patients center

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around creating a safe delivery plan.

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It is absolutely essential to have a

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multidisciplinary care team that's taking

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part in the management of these patients.

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And that includes OBGYN and maternal fetal

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medicine, occasionally gynecologic oncology from

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a surgical perspective, urology, interventional

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radiology, diagnostic radiology, and OR nursing.

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It's a big team.

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Operative planning for these patients

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includes review of the imaging, particularly

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if placenta percreta is suspected.

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The ultimate goal of the multidisciplinary

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care team is to decrease the

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risk of peripartum hemorrhage.

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And so we may end up doing preoperative CTA

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or MRA for these patients if indicated for

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operative planning, although this is rare.

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And then patients may also undergo

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uterine artery embolization.

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So, as I mentioned, delivery is

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planned at 30 to 34 weeks gestation.

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Typically, patients, particularly with

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placenta percreta, will undergo a midline

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abdominal incision and then a transfundal

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uterine incision, rather than the low anterior

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incision that's classic for cesarean section.

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The fetus is delivered breech,

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and then the uterus is oversewn.

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If the patient is going to undergo uterine

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artery embolization, it happens at this time,

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after the fetus is delivered and

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after the uterus has been oversewn.

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After uterine artery embolization,

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patients with placenta percreta and

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sometimes advanced cases of accreta

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and increta will undergo hysterectomy.

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The approach of the surgery is largely

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dictated by the amount of vasculature

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that has been recruited by the placenta.

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So if there is significant vascular recruitment

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in a case of percreta, the surgeons may

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have to perform a radical hysterectomy

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rather than a standard hysterectomy.

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In that case, they would take a more

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lateral and extensive vascular pedicle.

Report

Faculty

Erin Gomez, MD

Assistant Professor of Radiology

Johns Hopkins Hospital

Tags

Women's Health

Uterus

Ultrasound

MRI

Gynecologic (Gyn)

Gynecologic (GYN)

Genitourinary (GU)

CT

Body

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