Imaging of placenta

PRESENTED BY : DR.JUHI PATEL

REFRENCES : RADIAOGRAPHICS, RADIOLOGY ASSISTANT, RUMACK.

IMAGING OF PLACENTA

Normal placental anatomy and morphology.Normal variants of placenta.Umbilical cord.Twin gestations.Pathologic conditions of the placenta.• Placental causes of hemorrhage.• Gestational trophoblastic disease.• Nontrophoblastic placental tumors.• Cystic lesions.

TO BE DISCUSSED:

Placenta is responsible for the nutritive, respiratory, and excretory functions of the fetus.

Color and power Doppler techniques permit direct visualization of placental vascularity, allowing assessment of both the uteroplacental and fetoplacental circulations.

Sonography remains the imaging modality of choice for evaluation of the placenta.

It is uniformly of intermediate echogenicity, with a deep hypoechoic band at the interface between the myometrium and basilar decidual layer.

Normal Appearance on USG:

The overall appearance of the placenta changes during the course of pregnancy, with the progressive development of calcifications.

Early maturation of the placenta increases the risk of adverse fetal outcomes.

Placental Maturation :

Grade 0

Grade I

Grade II

Grade II

Grade III

It is expressed in terms of thickness in the mid portion of the organ and should be between 2 and 4 cm.

Placental thinning (<2 cm): Has been described in systemic vascular and hematologic diseases that result in microinfarctions.

Thicker placentas (>4 cm) are seen in: Fetal hydrops.Antepartum infections.Maternal diabetes.Maternal anemia. Can be simulated by myometrial contractions .

Placental Thickness :

Typically, the placenta is located along the anterior or posterior uterine wall, extending onto the lateral walls.

Although usually discoid, the placenta can be variable in morphology.

Variant placental shapes include:Succenturiate.Bilobed.Circumvallate.Placenta membranacea.

Variants Of Placenta :

Succenturiate lobe : Is an additional lobule separate from the main bulk of the placenta. SIGNIFICANCE: Rupture of vessels connecting

the two components, retention of the accessory lobe with resultant postpartum hemorrhage

Bilobed placenta: Placenta with two relatively even sized lobes connected by a thin bridge of placental tissue.

Circumvallet placenta: Chorionic plate smaller than the basal plate with associated rolled placental edges.SIGNIFICANCE: Placental abruption and

hemorrhage.

Placenta membranacea : Thin membranous structure circumferentially occupying the entire periphery of the chorion.SIGNIFICANCE : Placenta previa, as a portion

of the placenta completely covers the internal cervical os

Umbilical Cord :The umbilical cord typically inserts centrally, but

eccentric and velamentous (outside the placental margin) insertions also occur.

Eccentric insertions are cord insertions that are <1 cm from the placental edge.

Velamentous insertion: here the umbilical cord inserts on the chorioamniotic membranes rather than on the placental mass.This membranous insertion results in a variable segment

of the umbilical vessels running between the amnion and the chorion, unprotected by Wharton jelly.

Importance of evaluation of placenta in twin gestation lies in deciding the chorionicity.

The increase in perinatal complications is correlated with placental chorionicity, with a higher rate of morbidity and mortality seen in monochorionic than dichorionic gestations.

Monochorionic twins are always monozygotic whereas dichorionic twins can be mono or dizygotic.

Twin Gestation :

US is capable of demonstrating chorionicity with a high degree of specificity and sensitivity.

Clear distinction of two placentas may be difficult, particularly if the two sites of blastocyst implantation are close.

In these cases, the twin peak sign and T sign can be helpful in defining chorionicity.

The twin peak sign is a triangular projection of placental tissue extending up the inter-twin membrane (opposed amnions) in dichorionic-diamniotic twinning. It is visible in the late first and early second trimester. Thickness of membrane : >=2 mm.

Twin peak sign in dichorionic-diamniotic twin gestations.

The T sign is a 90° intersection of the intertwin membrane with the single placenta in a monochorionic-diamniotic gestation. Thickness of membrane : approx. 1 mm.

T sign in a monochorionic-diamniotic twin gestation

Pathologic conditions of the placenta include :

• Placental causes of hemorrhage.

• Pathological conditions towards maternal side and within the placenta.

• Gestational trophoblastic disease.

• Nontrophoblastic placental tumors.

Antepartum hemorrhage remains an important cause of maternal and fetal morbidity and mortality.

Placenta previa and placental abruption account for more than one half of cases of antepartum hemorrhage.

Another condition called vasa previa is also associated with antepartum hemorrhage.

Placental Causes of Antepartum Hemorrhage :

It represents premature separation of the placenta from the uterine wall.

Although rare, third-trimester abruption is associated with an increased risk of preterm delivery and fetal death.

US is frequently performed to confirm the presence of abruption and assess the extent of subchorionic or retroplacental hematoma.

Placental Abruption :

The presence of blood in large enough volumes to be visible sonographically indicates retained hemorrhage that may remain symptomatic.

False-negative results can occur when blood dissects out from beneath the placenta and drains through the cervix.

Placental Hematoma :

Fetal side•Subamniotic•Subchorionic

Within the PlacentaMaternal side•Retroplacental

Subamniotic hemorrhage is contained within amnion and chorion and thus extends anteriorly to placenta but is limited by reflection of amnion on placental insertion site of umbilical cord. Subamniotic bleeding is rare.

Subchorionic bleeding dissects chorion and endometrium; when such bleeding involves margin of placenta, it is called marginal subchorionic hematoma.

Retroplacental bleeding is found behind placenta.

Placental hematomas appear as well-circumscribed masses with echogenicity that varies according to chronicity.Acute : Hypoechoic or anechoic.Subacute : Heterogeneously echogenic.Chronic : Anechoic.

Doppler interrogation should reveal absence of internal blood flow; this finding allows differentiation of hematomas from other placental masses

Placenta previa refers to abnormal implantation of the placenta in the lower uterine segment, overlying or near the internal cervical os.

Normally, the lower placental edge should be at least 2 cm from the margin of the internal cervical os.

The relationship of the placenta to the internal os changes throughout the course of pregnancy as the uterus enlarges.

Placenta Previa :

The diagnosis of placenta previa should not be made before 15 weeks gestation, and low-lying or marginal placental positioning should be re-evaluated later in gestation to confirm placental position before delivery.

Placenta previa can be subdivided according to the position of the placenta relative to the internal cervical os.

Subtypes Description

Low-lying placenta

Lower placental margin is within 2 cm of the internal cervical OS.

Marginal previa

Placenta extends to the edge of the internal OS but does not cover it.

Complete previa

Placenta covers the internal OS.

Central previa Central placenta is implanted directly over the internal OS.

It refers to the presence of abnormal fetal vessels within the amniotic membranes that cross the internal cervical os.

These vessels are unsupported by Wharton jelly or placental tissue and are at risk of rupture.

Rupture of these vessels can lead to catastrophic fetal hemorrhage.

Vasa Previa :

In cases of vasa previa, the abnormal vessels either connect :A velamentous cord insertion with the main

body of the placenta .Connect portions of a bilobed placentaPlacenta with a succenturiate lobe.

Given this association, vasa previa needs to be excluded in patients with variant placental morphology.

The diagnosis of vasa previa is made with Doppler US, which demonstrates vascular flow within vessels overlying the internal cervical OS.

As with placenta previa, patients with vasa previa diagnosed in the second trimester should be re-evaluated later in gestation. The vasa previa can resolve as the uterus enlarges and the relationship of the placenta to the internal os changes.

Towards Maternal Side

During the process of placental development and implantation, a defect in the normal decidua basalis from prior surgery or instrumentation allows abnormal adherence or penetration of the chorionic villi to or into the uterine wall.

This abnormal adherence of the placenta to the uterus can result in catastrophic intrapartum hemorrhage at the time of placental delivery, often necessitating emergent hysterectomy.

Placenta Accreta, Increta and Percreta :

Placenta accreta : chorionic villi attach to myometrium (more than 1/3rd ), rather than being restricted within the decidua basalis.

Placenta Increta : Chrionoc villi invade into the entire myometrium.

Placenta Percreta : Chorionic villi invade through the myometrium upto serosa.

Sonographic features of placenta accreta and increta include: loss of the normal retroplacental clear spaceprominent placental lacunaeincreased vascularity at the interface of the

uterus and bladder.

Of these various sonographic features, the presence of prominent placental lakes has the highest positive predictive value. Lacunae are characterized by ill-defined margins, irregular shape, and turbulent flow.

Within The Placenta

The vast majority of hypoechoic foci in the placenta represent :

Placental lakes. Intervillous space thrombi Placental infarction.Placental cysts.

The term placental lakes may also refer to intervillous vascular spaces that appear hypo to anechoic and demonstrate low-velocity laminar flow on colour Doppler images.

Intervillous space thrombi form due to focal fetal hemorrhages that rapidly thrombose in the maternal blood pool of the intervillous space.

Most intervillous space thrombi are visible as hypoechoic foci smaller than 1–2 cm and are of limited clinical significance.Lesions larger than 3 cm may be indicative of underlying placental disease

Placental infarction : can occur focally or throughout the placenta. Thought to have vascular etiology.

They appear as cystic lesions with echogenic rim within the placenta, without internal vascularity.

True placental cysts occur on the fetal surface of the placenta, typically near the cord insertion.

The majority are simple with internal echogenicity identical to that of amniotic fluid.

The common feature for this group of disorders is the abnormal proliferation of trophoblastic tissue with excessive production of β–human chorionic gonadotropin (β-hCG).

It encompasses :hydatidiform moles (most common).Invasive moles.Choriocarcinoma.

Gestational Trophoblastic Disease :

First-trimester bleeding is one of the most common clinical presentations for this group of disorders.

Other clinical signs and symptoms include :rapid uterine enlargementexcessive uterine size for gestational agehyperemesis gravidarum preeclampsia that occurs in the early second

trimester.

It is classified into two major types :Complete (more common)Partial

Complete moles result from fertilization of an empty ovum with subsequent duplication of the paternal chromosomes.

This chromosomal anomaly causes early loss of the embryo and proliferation of the trophoblastic tissue.

Hydatidiform Mole :

At US, complete moles appear as a heterogeneous echogenic endometrial mass with multiple variable-sized small anechoic cysts, giving the appearance of a “snowstorm”.

There is no identifiable fetal tissue.

At color Doppler interrogation, increased vascularity with low resistance waveforms can be identified in the spiral arteries of the uterus.

Partial hydatidiform moles result from fertilization of a normal ovum by two sperm.

At sonography, partial moles appear similar to complete moles but are differentiated by the presence of fetal tissue.

Invasive Moles : Invasive moles represent deep growth of the abnormal tissue into and beyond the myometrium, sometimes with penetration into the peritoneum and parametrium.

They need to differentiated from Choriocarcinoma.

It is the malignant trophoblastic disease of placenta.

Invasive moles and chroriocarcinomas are largely indistinguishable at imaging.

At sonography, both appear as heterogeneous, echogenic, hypervascular masses.

Choriocarcinoma:

Choriocarcinoma Invasive moles

Areas of intralesion necrosis and hemorrhage can be seen within

Locally invasive

Capable of metastasizing, frequently manifesting with lung and pelvic metastases.

Non metastasizing neoplasms

Nontrophoblastic placental tumors are quite rare.

They are mainly :Chorioangiomas (less than 1% of pregnancies)Placental teratomas (extremely rare)

Placental teratomas are similar in appearance to chorioangiomas, but are differentiated by the presence of calcifications.

Nontrophoblastic Placental Tumors:

Chorioangiomas are the most common benign vascular tumour of placental origin.

They are essentially hemangiomas of the fetal portion of the placenta, supplied by the fetal circulation.

Although the vast majority are small and of no clinical significance, large (>5 cm) or multiple lesions (so-called chorioangiomatosis) stress the fetal circulation and can be associated with complications such as hydrops, thrombocytopenia, intrauterine growth retardation, and an overall increase in antepartum mortality

Most of them are incidentally identified.

These lesions appear :well-circumscribed, rounded, hypoechoic masses

protruding from the fetal side of the placenta.Usually contain anechoic cystic areas.And some heterogenous areas caused by internal

hemorrhage / degeneration.Can be pedunculated.

Most are located near the cord insertion, and Doppler imaging reveals low resistance pulsatile flow wihtin the anechoic areas which represents a large feeding vessel.

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