Imaging of Abnormal Placentation - HD

Introduction

Hello, my name's Juan.
I'm an associate professor from the University
of Washington in Seattle,
and the topic of my lecture today is Imaging
of Abnormal Placentation.
In this lecture, I'll be describing
what a normal placenta looks like,
and then imaging findings in abnormalities
of the placenta as well.

Role and Imaging of the Placenta

The placenta is a central support organ
for the developing fetus, serving as a site
of maternal fetal exchange of oxygen, carbon dioxide,
and nutrition.
Ultrasound is the primary imaging tool for the placenta,
but MR is used primarily as an adjunct imaging tool.
So in this lecture, we will review the normal sonographic
appearance of placenta, review anatomic variance,
abnormal placentation cases,
and then look at an approach to selected anomalies
with preferred imaging modality.
So in imaging the placenta, we will look at the location,
the shape, and the number, the abnormalities
of cord origin, placental grading, placental thickness,
and morphology as well.

Normal Sonographic Appearance

Placenta can be identified as early as six weeks
by transvaginal ultrasound
and 10 weeks by transabdominal ultrasound.
It is seen as an area of focal thickening of hyperechoic rim
of tissue around the gestational sac
and distinct from the myometrium from 12 to 13 weeks.
Color flow doppler evaluation can show intervillous blood flow,
and by 14 or 15 weeks, the placenta is well-formed
and can be seen easily.
The retroplacental complex is a prominent hypoechoic area
composed of decidua, myometrium and uterine vessels,
and they should never be greater than one
to two centimeters in thickness.
The red outlines the retroplacental complex in this
particular patient.

Placental Grading

Placenta is graded using the Grannum classification.
Grade zero is placenta, which is homogenous.
The chorioamnion plate is even throughout in this
and usually seen in the late first trimester
or early second trimester. Grade one placenta is when a few
echogenic densities are seen ranging from two
to three millimeters in diameter.
The chorionic plate shows small indentations
and is seen in the mid second and early third trimester.
Grade two placenta is when the chorionic plate shows marked
indentations appearing as calcific densities,
which extend into the placental substance,
but does not reach the basal plate.
The echogenic densities also are
more in number compared to a grade one placenta.
The basal layer also becomes punctuated with linear echoes,
which are enlarged with their long
axis parallel to the basal layer.
This is seen in the late third trimester,
usually about 30 weeks to delivery.
Grade three placenta is seen when there's complete
indentations of the chorionic plate through
to the basal plate creating cotyledons.
And this is seen in the 39 weeks to post dates.

Hypoechoic Foci in the Placenta

The vast majority
of hypoechoic foci in the placenta are intervillous space
thrombi or decidual septal cyst, commonly referred to
as placental lakes.
The term placental lakes also refers
to intervillous vascular spaces that appear hypoechoic
and demonstrate low velocity laminar flow on color.
Doppler images. Septal cysts are related
to focal degeneration within the maternal decidua.
And most intervillous space thrombi
and decidual septal cyst are one to two centimeters in size
and are limited and are of limited clinical significance.
True placental cyst occur on the placental fetal on the
fetal surface of the placenta,
typically near the cord insertion
and appear to develop at the subchorionic
foy of fibrin deposition.
Majority are simple with internal echogenicity identical to
that of amniotic fluid as seen in this particular case
with the cyst seen adjacent to the fetal long bones
and the cyst seen on the placental surface
or the fetal surface of the placenta on the gross specimen.
The prevalence of placental cyst is thought
to be in the range of two to 7%, but most are small
and usually not noticed.

Abnormalities of Placental Shape

Now we should look at abnormalities of placental shape.
Succenturiate placental lobe is seen when there's fetal
vessels traversing between the lobes
as seen in this particular explanted gross specimen
with a small placental accessory placenta seen here
and fetal vessels seen in between.
This is represented in the diagram over here
with the main placental bulk
and then vessels coursing in between membranes
to the smaller placental tissue.
The fetal vessels can also,
these fetal vessels can also seem to cross the internal os,
in which case it would be a vasa previa.
Color doppler is used to show these placental vessels
as seen on this particular case.
Over here, these vessels are not seen well on the B mode
image, but are seen well on the color doppler.
The succenturiate lobe carries an increased risk
of retained products of conception,
and hence needs to be diagnosed intrauterine.
A bilobate placenta is a variant of lobation in this,
the two lobes are equal in size with the cord origin in
between the two lobes.
There's usually a thin bridge of tissue in between
as seen in this particular case
with two equal placenta seen anteriorly and posteriorly
and fetal vessels seen coursing in between.
And the cord origin seen in
between these two placental lobes.

Abnormalities of Attachment

Marginal Cord Insertion

Marginal cord insertion is seen when the cord originates adjacent
to the placenta from the membranes seen in this particular,
gross specimen.
This is a placental tissue fetal membranes,
and the cord is seen to originate at the edge
of the fetal membranes on this image
with the light shining through in the back,
you can see the vessels pretty well within the membranes as well.
Color doppler is used
to find the cord origin in all these cases,
and so in this particular case,
you can see the placental tissue anteriorly
membranes running in between, cord vessels running in
between the membranes and the cord originating out along the
lateral edge of the uterine wall.
These cord vessels lack placental support
and hence there's an increased risk
of IUGR, fetal cord thrombosis
or cord rupture at delivery.
This can result in twin transfusion
in twins as well.

Vasa Previa

Vasa previa is seen when there's
abnormal fetal vessels within the amniotic membranes
that cross the internal os.
There is risk of rupture when the supporting membranes
rupture and these abnormal vessels either connect a
succenturiate cord insertion with the main body
of the placenta or connect portions of the bilobate placenta
or a placenta with the succenturiate lobe.
Doppler ultrasound is used
to demonstrate flow within vessels overlaying the internal
os as seen in this particular case.
This is the cervix with the internal os,
and here's a placenta with the vessels crossing the os
suggesting a vasa previa.
Transvaginal ultrasound may be necessary to diagnose vasa previa
as seen in this particular case.
The cord origin was seen further up there was an succenturiate loop
and transvaginal ultrasound shows vessels crossing the
internal os in this particular case suggesting vasa previa.

Marginal Cord Insertion (Battledore Placenta)

Marginal cord insertion, also known as battledore placenta,
is when there's eccentric cord insertion on the placenta within 20
millimeters of the edge seen in this particular case,
placental tissue anteriorly
and the cord originates at the edge of the placenta.
Similarly, color doppler shows a similar thing
with the cord originating at the edge
and in this particular case, color doppler,
as I mentioned, is necessary to evaluate
for the cord origin,
and this is usually marginal cord origin usually does not have any
morbidity associated with it.

Circumvallate Placenta

Circumvallate placenta is when placental membranes attach to the fetal surface
of the placenta as seen in this diagrammatic representation.
A normal membrane inserts at the edge
of the placenta in a circumvallate placenta,
the edge traverses over the placenta for a distance,
and then attaches to the placenta.
This margin can become fibrous
and appear echogenic on ultrasound.
This can result in bleeding PROM
or premature rupture of membranes, IUGR
and preterm labor as well.

Placenta Previa

The placenta migrates five millimeters per week
and in previa the placenta edges close
to the internal os.
Previa can be diagnosed in second trimester
and can also resolve by third trimester.
There are different classifications of placenta previa.
Complete previa is when it completely covers the
internal os as seen in this particular diagrammatic
presentation, partial previa seen when it partially covers the os.
Marginal previa seen when it's within two centimeters of the internal os.
There's an increased risk of placenta previa with increasing age
and increasing parity as well.
5% of these placenta previas are associated with accreta
spectrum and may need transvaginal ultrasound
or transperineal ultrasound for confirmation.
This is a case of complete placenta previa.
Here's the cervix with the internal os
and the placenta sitting on top
of the cervix and the internal os.
So this is a case of complete placenta previa
with the placenta sitting on top of the internal os,
a partial placenta previa
where the placenta partially covers the internal os,
which is represented by these calipers.
And then a marginal previa
where the placenta just touches the internal
os but does not cross it.
The transvaginal ultrasound is used in assessing placenta previa
and based on this particular study from Obstetrics and Gynecology in 1990,
they had a hundred patients with suspected placenta previa
who had transvaginal ultrasound.
99 had the diagnosis confirmed on cesarean section,
and transvaginal ultrasound had a sensitivity
of 87.5% specificity of about 99%
positive predictive value of 93%
and negative predictive value of 98%.
They also found that transvaginal ultrasound was not
associated with increased bleeding when performed
during ongoing vaginal hemorrhage.
Transperineal or translabial ultrasound can also be
performed if transvaginal ultrasound is difficult to perform.
In another study from Obstetrics and Gynecology in 1997,
based on a prospective cohort,
they had one hundred and thirty one
patients with suspected placenta previa
or low lying placentas greater than 15 weeks
of gestation, who had both transabdominal
and transvaginal ultrasound for detection
of placental location.
66 women of these had suboptimal visualization
by transabdominal only,
and 65 women had adequate visualization,
but with both transabdominal
and transvaginal ultrasound, 48 of these cases
were confirmed by transvaginal ultrasound
with 25 being low lying and 23 being marginal.
17 cases were reclassified
after the transvaginal ultrasound
with a placental location change,
but not changing the diagnosis.
So based on this, they suggested
that the transvaginal ultrasound may result in
reclassification of placenta previa
and hence if the placenta is low lying
or if the fetal head is in the view,
transvaginal ultrasound is necessary for further analysis.
This is a representative case showing a fetus
with a head overlying the internal os.
This is the cervix. It is very difficult
to see the internal os
because of the fetal head and the bladder.
A transvaginal ultrasound was performed even
with the transvaginal ultrasound.
You can see the placenta posteriorly.
However, the placental edge is difficult to
evaluate due to the fetal head.
After gradual and manually displacing the fetal head,
you can see that the fluid with the fluid dispersed in
between the fetal head and the internal os,
it is now easier to visualize the internal os
with color doppler, no vessels
or placental tissue was seen overlying the internal os
and the distance to the placental edge was about
1.7 centimeters.
Classifying this as a low lying placenta
and not a placenta previa.

MR Evaluation of Placenta Previa

MR can be used for further evaluation of
suspected placenta previa cases,
especially if the lower edge is difficult to discern.
This is a patient with a complete previa.
You can see the placenta overlaying the internal os
completely patient with partial placenta previa.
Here's the cervix with the internal os
and part of the placenta overlaying the internal os
and a patient with a marginal placenta previa
with the internal os seen here
and the placenta just touching the internal os.

Abnormal Placental Attachment (Accreta Spectrum)

Some of the placentas can also undergo
abnormal attachment and result in accreta, increta or percreta.
These result from defect in the normal decidua basalis from either
prior surgery or instrumentation
and allow for the abnormal adherence of the placenta
and penetration into the chorionic villi
and sometimes into the uterine wall as well.
They are associated with high morbidity from maternal
bleeding of almost 90%
and require transfusion with a 7% mortality
and a 15% chance of uterine rupture with percreta.
So accreta are seen most commonly in about 80%
of cases when there's superficial invasion
of the decidua layer increta when there's invasion into the
uterine wall, but not beyond the uterine wall seen in about 15%
and percreta seen in about 5%
of cases when there's involvement of surrounding serosa
or adjacent organs.
Sonographic features of placenta accreta include loss
of normal retroplacental clear space anomalies
of the bladder myometrium interface, prominent placental lacunae
and increased vascularity of the interface
of the uterus and the bladder.
Of these, the prominent placental lacunae have the highest
positive predictive value.
Lacunae are characterized by ill-defined margins
and irregular shape and show turbulent
flow on color doppler.
The overall sensitivity
and specificity of ultrasound for diagnosis
of placenta accreta has been reported to be about 77
to 93% and 71 to 96% respectively.
Placenta accreta can be difficult to diagnose on ultrasound,
but can be seen as thinning of the uterine wall
as seen in this particular case with abnormal vascularity,
which is not readily visualized
in this particular case.
These are difficult to diagnose prenatally
and may be easily missed.
Increta when there's invasion of the uterine wall is seen
as areas of increased vascularity
as seen on this color doppler image with areas of
lacunae formation seen in this particular case.
Placenta percreta is when there's invasion
of surrounding organs
and invasion of the uterine wall all throughout these can be
seen in this particular case where there's interface
with the bladder is lost
and you can see placental tissue extending outwards along
the anterior part of the placenta.

MR Findings in Placenta Accreta

MR has been used to evaluate for placental invasion
and it's most useful in cases
where the sonographic findings are equivocal
or when the placenta has a posterior location.
MR findings of placenta accreta include
abnormal uterine bulging heterogeneous placental signal
intensity on T2 weighted images
and presence of dark intraparenchymal bands
related to the lacunae.
On the T2 weighted images.
The overall sensitivity
and specificity of MR is about in the high eighties
and between 65 and 100 percent respectively.
So in this case you can see invasion
of the anterior abdominal wall seen here as loss of the myometrial low signal intensity with extension
of the placenta outwards.
This is a patient with a placenta percreta seen
as lateral extension of the placenta into the lateral pelvic organs and broad ligament.
Given the difficulty in making an accurate antepartum
diagnosis of placenta accreta,
some authors recommend a two stage approach beginning
with ultrasound in patients with clinical risk factors
and then proceeding to MR for equivocal cases.
This particular patient chose an area of placenta percreta seen as areas of
lacunae formation involving not only the lower uterine wall,
but also the cervix with increased vascularity
seen on color doppler.
And then MR confirming the findings seen as areas
of heterogeneous signal intensity within the placenta and the myometrium and lateral
and posterior extension seen here on these images on the
axial and sagittal images.

Placental Hemorrhage and Abruption

Now we'll evaluate some causes of hemorrhage with placenta being the culprit.
Placental abruption.
Placental abruption is seen when there's premature separation of placenta from the uterine wall.
There's increased risk of preterm delivery
and fetal death in these cases.
Small placental abruptions have excellent prognosis.
Larger ones which are greater than 50% in size have poorer
prognosis if the fetus has bradycardia, that is associated
with poor prognosis as well
and they're most commonly seen in placenta
that have marginal or eccentric origin of the cord.
Other types of placental abruption include retroplacental
and preplacental hemorrhages.
Retroplacental is seen behind the placenta
and is the most worrisome
because of devascularization of the placenta.
Preplacental hemorrhages are seen on
the surface of the placenta.
This is an example of a preplacental abruption
with a large fluid collection seen anterior
to the placenta. In a chronic placental abruption,
septations and areas
of nodularity can be seen within this fluid collection
suggesting a chronic appearance.
This is a patient with an old retroplacental abruption seen
as an area of avascular fluid
collection behind the placenta.
CT has been used for evaluation
of placental abruption mainly in patients with trauma
and these can be seen as areas
of devascularization if contrast is administered
or areas of hemorrhage within the placenta
seen in this particular case with areas
of devascularization.
And then high density areas suggesting hemorrhage within the placenta.

Placental Hematomas

Placental hematomas are well circumscribed masses
and their echogenicity varies according to the age.
They can occur on the preplacental or subchorionic site
or the maternal retroplacental site
or within the placenta as well.
They may be hypoechoic
or anechoic in the acute phase,
heterogeneously echogenic in the subacute phase
and echoic in the chronic phase.
Doppler should reveal absence of blood flow within the area of hemorrhage
as seen in this particular case
with the heterogeneous collection within the placenta
with no flow on color doppler.

Abnormalities of Size and Placental Masses

Moving on to abnormalities of size
and masses within the placenta.
The placenta should not be thicker than four centimeters in
size and the placenta grows at about
one millimeter per week.
Normal thickness is equal roughly
to the gestational age in millimeters.
Placental enlargement or placentomegaly is a nonspecific finding
and can be seen with maternal or fetal abnormalities.
They can be associated with IUGR hydrops or macrosomia.
There is an increased risk
of placental insufficiency regardless of cause.
This is a patient who had a placenta
that was 7.6 centimeters in thickness and obviously thickened
or increased in size.

Chorioangiomas

Placental masses, chorioangiomas,
a benign placental hemangiomas.
They arise on the fetal portion of the placenta
and are supplied by the fetal circulation.
They're well circumscribed, homogenous hypoechoic
or mixed echogenicity masses protruding from the fetal
side of the placenta.
Most are located near the cord insertion
and doppler does reveal substantial vascularity
or large feeding vessels.
They could be solitary but could be multiple as well
and are associated with increased AFP levels.
They can cause polyhydramnios
and hydrops in these patients.
Follow up of these patients for evaluation
of hydrops is important due to their high vascularity.
This is an example of a chorioangioma
with a heterogeneous mass seen along the fetal surface
of the placenta with increased vascularity seen on color.
Doppler pathology specimen shows a heterogeneous mass seen near the cord
insertion in this particular case.
Another case with a chorioangioma shows increased vascularity
within the mass seen on this particular image
with a heterogeneous appearance, which may be due
to internal hemorrhage as well.

Gestational Trophoblastic Disease

Moving on to the gestational trophoblastic tumors,
the classification suggest either hydatidiform moles invasive moles
and choriocarcinomas
and the hydatidiform moles could be complete or partial.
So hydatidiform moles are two major types, as we said, complete
or partial complete is due to fertilization of an empty ovum
with subsequent duplication of the paternal chromosomes.
46 XX
or 46 XY ultrasound in a complete mole shows a heterogeneous echogenic endometrial mass
with multiple variably sized small anechoic cysts giving the
appearance of a snow storm.
There's no identifiable fetal tissue in these cases.
And color doppler shows increased vascularity
with low resistance waveforms seen within the spiral arteries of the uterus.
Theca lutein cysts can be seen in about 50% of complete moles
and are caused by hyperstimulation of the ovaries due
to the excessive production of beta hCG
by the abnormal trophoblastic tissue.
This is a patient with a complete hydatidiform mole
with an enlarged ovaries seen showing multiple cysts suggesting
theca lutein cysts.
Another case of complete hydatidiform mole showing the snowstorm
appearance within the uterus
and the MR showing increased intensity within this
tissue on T2 weighted images
with heterogeneous vascularity seen on post
contrast images.

Partial Hydatidiform Mole

Partial hydatidiform mole is seen when there's
fertilization of a normal ovum by two sperms giving 69 XXX or 69 XXY abnormality.
Ultrasound shows a similar appearance to complete moles,
but are differentiated by the presence
of fetal tissue seen in this particular case when the
placenta is thickened with multiple cysts within it.
But in addition, placental tissue
or fetal tissue seen
as fetal parts here are seen within this patient as well.
MR can be used to determine the extension of the molar tissue to the parametria outside the uterus.
MR findings are frequently non-specific
and can mimic retained products of conception.
They appear heterogeneous tissue distending the uterine
cavity with predominantly low signal intensity on T1 weighted images, high signal intensity on T2 weighted
images and evident enhancement on post contrast images.
Focal areas of hemorrhage and cystic spaces can be seen as well in partial moles.
Abnormal fetal tissue can be seen.
It is important to identify normal myometrium in these
cases, which appears as a hyperintense layer
surrounding the molar tissue,
as this helps in differentiating between invasive
and noninvasive disease.

Invasive Mole

Invasive mole is seen when there's deep growth
of abnormal tissue into
and beyond the myometrium sometimes penetrating into the
peritoneum and parametrium.
This is a case of a 34-year-old female
with rising serum beta HCG.
After complete evacuation of a complete molar pregnancy,
heterogeneous tissue was seen within the uterus
with increased vascularity MR was performed, which shown
heterogeneous tissue extending
through the C-section scar.
Cesarean section was performed several years previously
and there's no evidence of involvement of the surrounding bladder wall.
However, on the coronal oblique images,
I can see the extension of the tissue out into the parametrium
with increased vascularity seen as signal voids.
In this particular case, this is a 20-year-old
who had an invasive mole after three months
after an abortion.
Coronal oblique T2 weighted images demonstrate
heterogeneous areas of hemorrhage within the tissue expanding the endometrial cavity.
Myometrial invasion is noted along the left lateral wall
and anteriorly seen here with disruption
of the junctional zone.
There's no evidence of extrauterine extension
of disease in this particular case.

Choriocarcinoma

Choriocarcinomas are similar to invasive moles
but are capable of metastasizing, frequently manifesting
as lung and pelvic metastasis.
Approximately 50% arise after a molar pregnancy, 25%
after abortion and 25% after a normal pregnancy.
MR imaging can have a role in demonstrating myometrial
and parametrial invasion.
Choriocarcinoma is usually seen as a intrauterine mass
with heterogeneous signal intensity on T2 weighted images
and marked enhancement on post contrast images findings
that reflect high vascularity in these cases.
Tumor vascularity can also be reflected by focal signal voids seen within
on the T1 and T2 weighted images.
Myometrial invasion is seen as
high signal intensity foci within the myometrium,
which demonstrate enhancement on post contrast images seen
in this particular case along the posterior
myometrium enhancing.
Parametrial soft tissue is characteristic of local spread.
MR imaging may help detect metastatic disease,
particularly in pelvic organs and lymph nodes as well.
This patient had a choriocarcinoma extend along the lateral
pelvic wall, seen as enhancing tissue along the
right lateral pelvic wall.
This is a patient with metastasis to the lungs.
The uterine disease was absent
with nothing seen within the uterus on MR,
but the lungs showed multiple nodules suggesting metastasis.

Conclusion

So in conclusion, abnormalities
of the placenta are important to recognize due
to the potential for maternal
and fetal morbidity and mortality.
Ultrasound is the dominant imaging modality
for evaluation of the placenta.
MR can be used for invasive placental processes.
CT has limited role and is mainly used in trauma
and gestational trophoblastic disease.
Thank you very much.