Use of MRI in Pregnancy - HD

Introduction

Hi, I am Debbie Levine.
I'm a professor of radiology at Beth Israel Deaconess
Medical Center and Harvard Medical School.
And today I'm gonna be talking about use
of MR in obstetric diagnosis.
Hello. Today I'm gonna be talking about use
of MR in pregnancy.
And you might think that this is an unusual talk
for an ultrasound course,
but the bottom line is we're going to use ultrasound
as a first line modality
and then use MR when we have additional questions
that can't be answered by ultrasound.
So I'm gonna be talking about use
of MR in pregnant patients for pelvic pathology
to assess placental abnormalities
for looking at abdominal pelvic pain.
And then for fetal MRI
to actually look at the fetus and the fetal anatomy.

Safety Considerations for MR in Pregnancy

The very first thing to mention is that it's very important
to have a discussion with the patient about the risks
and benefits of MR.
We don't know of any harmful effects for exposure,
MR, but because of the potential
and unknown effects, we limit the duration of exposure.
And again, just like any imaging studies,
we perform MR only when the diagnostic benefit is believed
to outweigh the theoretic risk.
Now, these statements are based on studies at 1.5 Tesla, and
although stronger magnet strengths, for example,
three Tesla have been approved
by the FDA in the United States,
I'm still a little bit hesitant about using those in
pregnancy just because I wanna do the least to every pregnancy.
And 1.5 T I think gives us really nice signal to noise.
But it doesn't have the same potential heating effects
that three T have.
Now, early on, we didn't do MR in the first trimester,
but since that time we found
that there's no known harms in the first trimester.
And so we have a statement
that was published in radiology in 2004 saying in cases
where the referring physician
and the attending radiologist can defend that the findings
of the MR procedure have the benefit to affect the care
of the mother and fetus, the MR procedure can be performed
regardless of the trimester.
So this is really helpful.
For example, if you have a patient
with possible appendicitis,
and you can't see the appendix with ultrasound,
and of course it makes a difference to patient care,
then MR is gonna be a much better test than, for example, CT
with a known radiation exposure.
But if you're looking at a fetal abnormality in the first
trimester, you're gonna see that better
with ultrasound than with MRI
because the fetus is just too small at 13 weeks
to see well with MR.
And so that would not be a case
where you would wanna perform an MRI.

Contrast in Pregnancy

What about contrast in pregnancy?
The contrast that we use in MR is gadolinium,
and this is a heavy metal.
It's excreted by the fetal kidneys into the amniotic fluid
where it's swallowed by the fetus
and then it sticks around for a while.
And the half-life in amniotic fluid isn't well known.
Gadolinium has been shown
to slightly retard development in rats at only two
and a half times the human dose, and
therefore it's not recommended
unless the benefit outweighs the risk,
which is very unlikely in most cases of pelvic MR.

Sedation

The next question that frequently comes
up is about sedation.
And my own anecdotal experience is
that claustrophobia is very common in pregnant women
undergoing MR.
And to avoid this, we put the women
feet first into the magnet.
Most women can be reassured and don't require any sedation,
but for those who give a history of claustrophobia,
then you can give some premedication.
And a drug like Xanax is short acting
and it's safe in pregnancy.
This is less of a problem with the short bore magnets
where if a woman's more than five feet four
in the United States,
that she'll have her head sticking out of the magnet.
Of course, before giving any medication like Xanax,
you'd wanna talk to the patient's clinician.

Maternal Pelvic Indications for MR

Adnexal Masses

Let's now go into some reasons why you might wanna
do MR in pregnancy.
And the first one of those is for adnexal masses.
It's been shown that MR is helpful to describe the organ
of origin of a mass, the nature of the mass,
and to decrease the need for surgery during pregnancy.
Here's an example of somebody who'd been hyperstimulated.
You can see three gestational sacs here.
She actually had quadruplets
and you can see one hyperstimulated ovary down in the
cul-de-sac and this great big mass ovary
with peripheral hemorrhagic follicles.
Classic example of massive ovarian edema.
It had been unclear on ultrasound why
the ovary was enlarging.
Sometimes torsion can be very difficult to diagnose
with just ultrasound
and MR can be helpful in those cases.
Here we've got two hyperstimulated ovaries,
but the right one is larger than the left
and the stroma is much more edematous in this
patient who had torsion.

Fibroids

Now fibroids were of course going to usually diagnose
with ultrasound,
but sometimes a patient will be having pain
or sometimes she'll have an unusual mass
and we won't quite be sure what is going on in those cases.
MR can be helpful. Here's a patient in the first trimester
with a great big necrotic mass.
We were able to see her ovaries separate from this mass,
but we couldn't tell for sure if it was a fibroid or not.
And we were worried that it might be something else.
We waited till the second trimester
for the MR since she wouldn't have had surgery in the
first trimester anyway.
And we could tell that this had a broad base
of attachment to the uterus.
It was classic necrotic fibroid.
Now I have a lot of experience doing MR for patients
with right lower quadrant pain
and we always do an ultrasound first.
And in this case we did an ultrasound first
and her pain was located right over her fibroid.
And we said, this is probably due to
fibroid degeneration that's causing her pain.
Her pain is localized there.
And the clinician said,
how do you know she doesn't have appendicitis as well?
And we went back and forth quite a bit about whether an MR
would be helpful in this case.
And since we couldn't see the appendix with ultrasound,
we went ahead and did the MR.
But nonetheless, it's a nice example of
what a fibroid looks like when it's acutely degenerating.
This is a T two weighted sequence.
You can see that the fluid is bright, the fibroids dark,
but there's areas of brightness within this fibroid.
And when you look on T one weighted imaging
where you've got fluid being dark,
we've got the bright appearance in this fibroid that's due
to the red necrosis, the hemorrhagic necrosis
of this fibroid during pregnancy.

Ectopic and Abdominal Pregnancy

Now, sometimes it can be difficult to tell
where exactly a pregnancy is located.
When you have an ectopic pregnancy in the first
trimester, it's pretty easy.
But when you have an abdominal pregnancy in the third
trimester, the clinical question is often,
where is the placenta so that they can appropriately plan
for the mode of delivery.
Here we've got a uterus that's empty down in the pelvis,
fetus that's in the peritoneal cavity.
And this placenta has a broad base
of attachment with the mesentery.
Now I know this is a pretty advanced gestation
because there's lots of cortical gyri here,
this third trimester.
And so the plan was made since this was such a late
diagnosis to deliver the baby in a couple
of weeks since the patient was stable
to deliver the baby through an incision into the belly,
leave the placenta in place,
and then treat the placenta so that it would regress
and then go in later on to remove it
to help not have such a bloody delivery by trying
to get the placenta out at the same time
as the baby was delivered.
Now, if we make the diagnosis of abdominal pregnancy earlier, this is not someone you wanna watch
because it can be a life-threatening
emergency to the mother.
And here we've got a uterus.
We've got the placenta
with a small attachment posterior to the uterus.
I know this is early on
'cause look at how smooth this fetal brain was.
This was about 18 to 20 weeks of gestation.
So this is an abdominal pregnancy.
Now, I mentioned before
that we don't give gadolinium in pregnancy as a rule,
but in a case like this where the pregnancy is not going
to be allowed to continue,
it would be a threat to the mother's life.
It's fine to give gadolinium
because you wanna know what the anatomy is
for the surgeon to make their planning.
And here what these reconstructed views you could see
the predominant vascularity going to this placenta
to help with the surgical planning.
Sometimes we're not quite sure what's going on.
And here we had a great big fibroid uterus
and this pregnancy kind of hanging out in the breeze.
Maybe there's one to two millimeters of either myometrium
or chorion here, but it didn't look normal at all.
And the patient when I asked her, said, oh, that's okay.
I have a bicornuate uterus,
but even a bicornuate uterus should still have substantial
myometrium around the gestational sac.
So even if this was a bicornuate uterus,
the pregnancy would be in an atrophic cornua.
So we went ahead and did an MRI.
And the nice thing about MRI is
that it lets you angle the images to the anatomy
that you need to see.
So here's a true coronal with lots of fibroids
and just a bit of the gestational sac, a midline sagittal
where we have this huge fibroid.
You can see the bladder here in the spine,
and it's not until you get an angle of an angled view
that you can see a right horn of this bicornuate uterus
and the left horn with very, very thin myometrium.
So this is not exactly an ectopic pregnancy,
it really is a pregnancy in an atrophic horn.
And so with this diagnosis, the patient continued her pregnancy,
and as soon as she had pain, she was delivered.
But nonetheless, she was able
to get fairly far along in pregnancy
before she was delivered by C-section near term.

Thin Lower Uterine Segment After Prior C-Section

Well, speaking of prior C-sections,
what do we do in the patients who have a very,
very thin lower uterine segment
after a prior C-section here, we're trying to look,
we've got bladder here, gestational sac here.
The patient's a little bit large,
we're getting shadowed out of the lower uterine segment.
We do a vaginal scan to try and see this area better,
but we just couldn't see it.
And here we're doing an MR to look
and see if there's any evidence of uterine rupture
or dehiscence.
So when you're doing these MRs you really need
to follow the myometrium around.
And here we're looking at myometrium
and down here we're looking at myometrium.
But in between you've got the fetal head,
you're not seeing the myometrium very well here.
What you need to remember when you're doing a case like this
is that the resolution of the MR the thickness
of those slices is usually around three millimeters.
And so you're going to get partial volume averaging.
It's gonna be very hard to see
that very thin lower uterine segment that measures only one
to two millimeters that has fat on either side of it.
So we need to be very careful about calling uterine rupture,
especially in a case like this
where the uterine contour is maintained.
So this is just a thin lower uterine segment,
but it's somebody who can be watched
and then if she has further symptoms,
they would finally decide to deliver her.
When we see a thin lower uterine segment like this,
frequently the clinicians will give steroids to ensure
that the fetal lungs are mature.
If the patient is far enough along in pregnancy,
we can also use MR.
If the clinicians are concerned about abruption, about half
of the time when there's a placental abruption,
when the placenta has lifted off the myometrium
and there's bleeding behind the placenta,
we just can't see it with ultrasound.
But if you do a T one weighted MR blood products are bright
and so we're able to clearly see the amount of blood.

Placental Abruption and Previa

Now placenta previa when there's bleeding is usually
painless and an abruption frequently causes a lot of pain.
So in this case that I'm showing you here,
the patient was having a lot of pain with vaginal bleeding.
So even though she had a placenta previa, the question was
how much of an abruption is present?
And here you can see that the majority
of the placenta is well attached.
There's just some blood clot over the lower uterine segment
cervix, and you can see
that high signal intensity extending into
the endocervical canal.
And so this patient was managed conservatively
and she got a couple more weeks
before she had another large bleed
and was eventually delivered.

Cervical Assessment

Now a lot of times we're doing a study for abdominal
or pelvic pain
and we'll just happen to notice that the cervix is short
and preterm labor can be a cause of pain.
And sometimes the patients don't even realize
that they're in labor and sometimes their
clinicians don't either.
So when you're doing one of these studies
to look at a fibroid for pain, to look for the appendix
to even look at the kidneys
or the gallbladder in the mother,
make sure you look at the cervix as well.
And if the cervix is short,
meaning less than three centimeters in the second trimester,
be sure to describe that in your report.
Every now and then we'll actually be asked
to do an MR in pregnancy for the cervix.
That might be for a patient for example, who is late
for prenatal care and they happen to do a pap smear
because she hadn't had one.
And it turns out she has cancer.
So we can use MR to stage cancers in pregnancy,
an uncommon indication for MR in pregnancy.
But if you're asked to do this, MR is the way
to go is for pelvimetry.

Pelvimetry

Why might we do this? Well, if the fetus is breech
and the mother wants a trial of labor, this allows
for accurate measurements without ionizing radiation,
you can get the patient in
and out of the magnet in less than five minutes.
And what you need to do is get your true sagittal
and an angled coronal.
And I just have this diagram in our MR suite
and if we ever need it, we can look up
what those normal values are.

Placenta Accreta

One of the more common reasons I get asked
to do an MR in pregnancy is for placenta accreta.
Placenta accreta is when you have abnormal attachment
of the placenta and it's associated
with significant morbidity
and mortality, you can have blood loss retained placenta
with associated infection postpartum,
and frequently these patients will end
up needing a hysterectomy.
So it's really important to know about
this prior to delivery.
It turns out that a history of cesarean section,
actually any instrumentation in the uterus
and a history of placenta previa puts the patient
at increased risk.
So if you have no C-section
and no previa, the underlying risk,
really the baseline risk is 0.25%.
But if you have four or more C-sections
and there is a placenta previa, then the risk is 67%.
Two outta three pregnancies will have a placenta accreta.
The sonographic findings are very well described.
Their loss of the hypoechoic, retroplacental myometrial zone
thinning or disruption
of the uterine serosa bladder interface,
focal exophytic masses and lacunar flow.
And really if you make this diagnosis with ultrasound,
there's no need for an MRI.
But every now and then people will wanna know, well,
what's the extent of the accreta
or the patient might have an unusual history
of the operation in her uterus, for example, myomectomy.
And it might be an area that's difficult
to visualize with ultrasound.
And those are the cases where MR can be helpful.
So in a small series that we did over a decade ago at Beth Israel Deaconess Medical Center,
this was the only case where MR was helpful.
Small area posterior placenta of invasion
of the myometrium that we couldn't see with ultrasound.

Deep Vein Thrombosis (DVT) Extension

Another reason you might get asked
to do an MR in pregnancy is to assess
for extension of a DVT.
DVT is pretty common in pregnancy affecting about one
to 2000 deliveries.
Of course we're gonna use ultrasound for thigh
and knee thrombus,
but if you're wondering about the pelvic
veins, MR can be very helpful.
You look for lack of flow in a distended vein.
So here's a relatively old patient, 52 years old.
She'd lied about her age at the time of IVF,
and so she got pregnant and had a large abruption.
And here you can see a large amount
of hemorrhagic fluid within the uterine cavity.
And she was put on bed rest and got leg pain.
And we could clearly see her DVT with clot from her
popliteal vein all the way up
to her common femoral vein even extending
into the iliac veins.
But the question was, how high up did the clot extend so
that they could figure out where to put the filter in?
Can they put it in from above
or does it have to go in from below?
And here you can see a venogram
with all of these collaterals.
So, here's the MR.
You can see the DVT a distended vein without clot.
You can see on a axial view
that the IVC here was compressed.
Now this was done on call in the middle of the night
and if I'd been there, I would've put the patient on her
side to get the weight of the uterus off the IVC
and hopefully see some flow.
But nonetheless, this compressed IVC means
that there's not clot within it.
And so they were able to get a filter in which you can see here on this image.

Abdominal Indications for MR in Pregnancy

Cholecystitis and MRCP

So let's now move out of the pelvis
and into abdominal indications for MR in pregnancy.
One of these will be cholecystitis in pregnancy.
Now again, we're gonna start with ultrasound
and almost always end with ultrasound.
In fact, we can even treat with ultrasound.
For example, here's a big distended gallbladder with lots
of sludge and debris within it in a patient who's having a
lot of pain at 29 weeks
and we're asked to put a drainage catheter in to take care
of her acute cholecystitis.
But sometimes there'll be a question that we can't answer
with ultrasound, for example, to look at the extent
of the stones within the biliary system.
And in that case, an MRCP can be helpful.
So we start with ultrasound.
If we can't answer the question, we go on to MRCP.
And in MRCP we get a thick slab,
heavily T two weighted sequence.
We look for dilated ducts and stones.
We do thin slices then in the axial plane looking
for smaller stones.
And then only those patients who need intervention go on
to the ERCP.
Here's an example of a patient with gallstones.
You can see them right here. Here you can see the fetus,
you can see there's pericholecystic fluid.
But look at the duct, it's gorgeous, it's normal,
it's non dilated.
So she recently passed a stone
and that's what was causing all of her symptoms.
And she was able to just be treated medically
and then was delivered by a C-section
with a cholecystectomy performed at the same time.

Urinary Tract Obstruction and MRU

What about the urinary tract?
Well, as I'm sure you know,
the urinary tract dilates in pregnancy
and typically the right side more so than the left side.
So the right ureter more than the left,
right hydronephrosis more than left,
and the distal ureter tapers just below the iliac vessels.
This will usually revert to normal by six weeks
postpartum patients are at risk for urinary tract infections
during pregnancy because they've got that increased glucose in their urine.
So when a patient presents with flank pain in pregnancy,
it can sometimes be very difficult to know, well,
is this the physiologic hydronephrosis of pregnancy
or is it due to a stone?
And we can try with ultrasound to look for a stone
and we should try really hard.
We should look for jets within the bladder.
It can be sometimes difficult to see jets
and they're not a hundred percent sensitive
or specific for obstruction.
So if you look at the pitfalls of ultrasound
and stone disease, the first one is the physiologic
dilatation in pregnancy.
That's just totally normal.
It can sometimes lead to an over distension syndrome.
And when you do have a stone, it can be very difficult
to see if it's not right there at the ureteropelvic junction.
If it's not right at the ureterovesical junction,
if it's in between those two
and it's in the ureter, it can be hard to see.
With ultrasound, even if you look for jets in the bladder,
15% of patients will have an absent ureteral
jet on one side.
So we can do MR
and select cases again, only those cases
where we haven't answered the question by ultrasound.
And the MRU, it's the same idea as the MRCP.
We get a thick slab, heavily T two weighted sequence,
we'll see stones as filling defects
will demonstrate the level of obstruction.
But the resolution does tend to be limited
and that's why we're gonna do thin axial slices as well.
But still small stones can be missed
and this can be difficult late in gestation.
So I've got two images here showing a dilated kidney,
a little bit of perinephric fluid,
a dilated ureter all the way down.
And do you all see the stone? It's right there.
Now hopefully we could have seen this with ultrasound.
But in this case an MRU was done.

Intestinal Obstruction

Let's now move on to another reason
for MR in pregnancy intestinal obstruction.
And usually if you think about a patient
with an intestinal obstruction, they're gonna go to CT.
But wouldn't it be nice in pregnancy to do an MR instead,
patients are at risk for intestinal obstruction if they have
prior adhesions
because of all the changes in the uterine size
that occurs during pregnancy.
So the three risk periods in pregnancy are at the end
of the first beginning of the second trimester.
So around 12 to 15 weeks
as the uterus grows into the abdomen.
Late in the third trimester is the head
descends into the pelvis.
Again, there's a change in the position of the uterus
and then in the peripartum as the uterus contracts.
So here's a patient who'd had prior surgery
who had a small bowel obstruction
and she actually was married
to someone in our radiology department.
So when she came in, what symptoms which she recognized
as a small bowel obstruction, she actually asked
to have an MR instead of a CT.
And I just loved this
because if you think about it, one of the problems
that we have with MR is all the intestinal peristalsis,
but if somebody really has a small bowel
obstruction, they have an ileus.
And that's what we're seeing here.
All these beautiful air fluid levels
and this transverse view, all these dilated loops of bowel.
But we've got some distal small bowel that's not obstructed.
We still have some gas in the colon.
And you can see this first trimester fetus here.
So this patient was able to be managed expectantly
and actually did not need any surgery during her pregnancy.

Abdominal and Pelvic Pain, Including Appendicitis

Let's see. So patient comes
in with right-sided pain.
We think about hydronephrosis, think about cholecystitis,
ovarian torsion abruption.
I've mentioned all of those earlier in this lecture.
Haven't quite gotten to appendicitis yet.
But for all of these, we're gonna start with ultrasound.
Absolutely start with ultrasound to look at all
of these different organs and regions in the uterus.
But if we're not sure, then we're gonna go on to MRI
And I like to use contrast for MR.
We actually use a negative oral contrast at my institution.
It's half of the contrast that you use for CT,
which is a barium sulfate suspension
and half of a iron solution to make the bowel dark.
You can do a lot of different sequences,
but the bottom line is you need something that is one
of these single shot techniques
because then if there's motion,
you're still gonna get information of anatomy.
You want something that gives you T one information.
Gradient echo is good for blood products, you wanna have a 2D time
of flight to look for clot
because a lot of times the veins, the flowing veins,
can be very difficult to tell from the appendix
as you're looking at anatomy.
And then you need some fat saturated images to look
for periappendiceal fluid.
So here we've got a very nice appendix that's easy
to see coming off of the cecum on a single image,
but a lot of times you just have to follow the appendix off
of the cecum on multiple views and follow it through.
And so it can be very helpful in PACS to scroll back
and forth to figure out where exactly the appendix is.
Here we've got an appendix, we've got nice bowel contrast that negative oral contrast,
but here the appendix is fluid filled.
It's not very distended here.
And then distally, it's very distended
and fluid filled, pretty classic appendicitis.
And here we've got a 13 weeker,
again, nice bowel filling.
But we've got the appendix there that's fluid filled
and a little bit of periappendiceal fluid.
So that was indeed appendicitis.
And here we've got another one
of these fibroids to drive us crazy right-sided fibroid, patient with a lot of pain.
An ultrasound in this case was not performed
and the MR showed a necrotic fibroid
and this is my favorite case in this series, a patient
with two prior C-sections
and she was in her early third trimester
with a negative ultrasound
and they tested her urine for an infection
and they said it was negative
and she really had severe pelvic pain.
And what you can see is gas in the bladder.
And so we actually suggested a urinary tract infection
and they went back and that indeed is what she had.
So you'd really rather not make the diagnosis
of a urinary tract infection on MR.
It's an expensive way to arrive at that diagnosis.
Well, that's abdominal and pelvic pain.

Fetal MRI

Let's now move on to the fetus.
And MR of the fetus is really a lot of fun,
but we shouldn't be doing it for the fun of it.
We should do it when there's additional information
that we need beyond that available with ultrasound.
The workhorse of fetal MR is one
of these single shot fast spin echo techniques.
The reason that these are so important is
that the fetus is constantly moving
and if you do a single shot technique,
you're gonna get a nice image.
And then if the fetus moves, it's gonna ruin the image
where the motion occurred,
but it won't ruin the other images within that sequence.
You use the fetal anatomy as what you want
for your reference for your image planes.
And each sequence acts as the scout for the next sequence so
that you can get the appropriate views.
You don't care if the maternal anatomy wraps
around onto maternal anatomy.
You wanna get a pretty tight field of view to look at the fetus as best you can.
T one weighted imaging is a little bit more problematic
because there's less intrinsic signal in the fetus
with the T one weighted images.
But we use it to look for example at the liver in cases of congenital diaphragmatic hernias.
We also use it to look
for meconium in the bowel when we're concerned about a bowel
issue and to look for blood and fat.
So here is an example of one type of T one weighted imaging,
a turbo flash that we might use.
And here's an example of a nice normal appearing liver.
And the anatomy is really exquisite here.
We just happen to have an entire arm with a thumb and
finger seen on the hand here you can actually see the
adrenal gorgeous views of the adrenal,
but it's really the brain that lets us see all
of this beautiful anatomy.
We get the side to side images of the cortical anatomy,
and we can see much better the development of the brain than we can with ultrasound.
So we again, don't use MR in every case,
but just when ultrasound needs more information.

Fetal Brain Abnormalities

So for example, here's a large Dandy-Walker malformation.
The cerebellar hemispheres are widely splayed apart.
There's associated ventriculomegaly
and the choroid plexus is dangling.
Now, normally when you have hydrocephalus due
to obstruction, the choroid plexus gets thinned out
because of the pressure.
But here the choroid plexus is very clumpy.
So that lets you know that there's been some bleeding.
So this is already a very poor prognosis,
but what we couldn't see very easily
with ultrasound was this huge area of porencephaly
because it's right underneath the skull.
It was just very difficult to visualize.
So that of course is gonna help with counseling the patient.
And here's another similar case.
We've got a lot of ventriculomegaly
and the ultrasound is showing this large area
of porencephaly.
So we've gone back to our ultrasound now that we've done
so much fetal MR
and we're able to say, we can suggest porencephaly
when we lose the lining of the ventricle, for example here.
And so we can actually use some of this information
that we've gotten with MR
and apply it back to ultrasound in this case as well.
We're seeing the anterior portion of the corpus callosum,
but not the posterior portion
because that had been destroyed as well from this hemorrhagic process.
After ventriculomegaly for encephalocele,
usually we will diagnose the encephalocele with ultrasound,
but the MR is gonna let us look at the
intracranial anatomy better.
Here we're seeing a totally dysmorphic brain associated
with an encephalocele.
And here's a kinked midbrain.
This kinked midbrain lets you know
that this is a very early dysmorphic process
and once you see a kinked midbrain like this,
there's no good prognosis to be expected.
Here's an encephalocele
with a pretty normal appearing brain.
And in this case the MRI is being done for surgical planning.
Here's a really big head in a fetus.
This head was measuring about 44 weeks.
There are all these hemorrhagic lesions within the brain
and it was very vascular.
And the question was, is this a vascular tumor?
Or a vascular malformation?
You can actually see the falx here
and the contralateral ventricle.
We did the MRI.
And again, you can see the very large head
and this big tumor, not a vascular malformation at all,
but a huge tumor, very invasive.
And this was helpful in saying that the vast majority
of the brain had been overtaken
by this aggressive tumor glioblastoma multiforme.
And that was helpful in counseling the parents
to not put the baby on life support after birth.
And here you can see after birth how large the head was
and how hemorrhagic the tumor was.
At the other end of the spectrum, here is a fetus
with a very small head.
The patient was obese at 16 weeks.
It was very difficult
to see any intracranial anatomy with ultrasound.
Transvaginal scanning was not helpful in this case
'cause the head was too high.
And on MRI you can see that there's a monoventricle, so
that's either gonna be holoprosencephaly or hydrocephaly.
Doesn't really matter. There's no good
prognosis for either one of those.
Now I've found MR to be particularly helpful in cases
of agenesis of the corpus callosum.
This actually is a pretty common finding.
About 0.3% of the general population have abnormalities
of the corpus callosum.
The problem we have with ultrasound is
that the corpus callosum development is not complete
until about 20 weeks.
And so frequently this can be missed on ultrasounds
performed in the second trimester.
Now we're hoping that with the cavum septum pellucidum
as a standard view on ultrasound,
that we'll be missing fewer of these cases of agenesis, but
nonetheless, they can still be missed prenatally.
The normal corpus callosum, beautiful sagittal
midline view will look like this.
And whenever you have ventriculomegaly you should
attempt to get that view to see the entire corpus callosum.
Here's an example of agenesis.
You have a teardrop shaped ventricle.
I'm doing a vaginal scan here
and we're seeing the frontal horns that are widely splayed apart.
They didn't have the normal orientation
and we don't see a normal cavum
of the septum pellucidum.
The reason I like MR so much for this diagnosis is
that you can look for the associated cortical abnormalities.
And for example, in this fetus we've got polymicrogyria
both in the midline
and around the outside so-called the so-called stenogyria seen here.
And just like ventriculomegaly,
it's the associated abnormalities
that are gonna be predicting the poor prognosis.
So with agenesis we look for the associated abnormalities
to predict prognosis.
Another reason that we might wanna do MR
in pregnancy is screening for abnormalities
which ultrasound is limited.
For example, tuberous sclerosis.
Tuberous sclerosis, we get a family history.
There are actually some genetic tests available,
but the only thing we can really do with ultrasound is look
for cardiac rhabdomyomas
and look for the tumors themselves,
the tubers themselves within the brain
and the obstruction that they cause.
So this was a patient who came in for screening 21 weeks
and had a rhabdomyoma.
We did an MR and saw this little dark
spot lining the ventricle.
Later on in pregnancy we saw even more
of these little dark spots,
these subependymal tubers and postnatally.
You can see all of these subependymal tubers in a neonate
with tuberous sclerosis.
Another reason we might wanna do MRs for conjoined twins,
of course you can make this diagnosis with ultrasound,
but when you're counseling the parents,
when you're preparing for delivery
and when you're counseling about the surgery
that's gonna be needed postnatally
MR can be very helpful.
So early on when we looked at our results of MR
of the fetal CNS, the biggest help
that we saw was doing a confirmatory ultrasound.
There's a lot of differences in abilities to perform
and interpret ultrasound
and we found that a large number
of patients could just have an ultrasound that would reassure the patient
and say that everything was normal.
But when the ultrasound was abnormal,
MR had a substantial number of changes in counseling,
major changes in diagnosis and changes in management.
Well, this was over a decade ago
and I can tell you now I think I'm
much better with ultrasound.
Again, I've learned from MR what to look for for the abnormalities with ultrasound.
And we're doing a much better job
of diagnosing partial callosal dysgenesis abnormalities
of development of the corpus callosum.
We're doing a much better job
of diagnosing cortical migrational abnormalities
and porencephaly.
When we look at MR of the fetal CNS,
it's least helpful when patients came in
and we said the ultrasound was normal
or when there was a neural tube defect.
In fact, I wouldn't do an MR for a neural tube defect
unless the patient is considering
having an in utero surgery.
MR was least helpful in demonstrating normal
and abnormal cortical, it was most helpful in demonstrating normal
and abnormal cortical anatomy in patients
with mild ventriculomegaly, mega cisterna magna
and arachnoid cyst.
And then of course in screening for abnormalities such
as tuberous sclerosis.

Chest Abnormalities

Well, let's move out of the head now
and into other areas of the fetus.
What about chest abnormalities?
Well, here we've got a nice example
of a congenital cystic adenomatoid malformation
or if you're a pediatric radiologist,
you might wanna call this CCAM for the congenital cystic adenomatoid malformation.
But what you can see is that there's an echogenic mass,
there's eversion of the hemidiaphragm,
there's cysts on MR.
You see a high signal intensity mass
flattening of the hemidiaphragm.
There's really no reason to do an MR in this case.
And again, if you do a good ultrasound,
you probably don't need an MR for the chest.
Now the CCAMs, the CAMs, they disappear in pregnancy.
And here we've got one where you could see it in the second trimester
by the early third trimester you couldn't see it
with ultrasound and you've just got a little
bit of scar tissue here.
And we know that after these babies are born,
sometimes on a chest x-ray you can't even see the
abnormality and you have to do a CT or an MR to look at it.
Well, I don't think we need to do MR in pregnancy to show
that these lesions resorb.
As long as the mediastinal shift is getting better,
there's absolutely nothing to worry about
and you wouldn't need any follow-up imaging
or confirmatory MRI. MR can sometimes be helpful when there's
complex congenital heart disease
and you want additional information.
For example, in this fetus,
the heart was located on the right side
and there was azygos continuation of the IVC,
which you can see by two great vessels in the chest here.
So we know there's some complex congenital heart
disease here.
We've got bilateral hyperlobation bronchi
and we've got polysplenia.
So this is heterotaxy syndrome.
Here's the stomach and here are the multiple little spleens.
I think where MR has made the most difference
for chest abnormalities is for hernias.
We can make the diagnosis of hernias on ultrasound
of course, but if the patient's considering having in utero surgery
for the hernia, then MR is helpful not just
to look at the organs that are up in the chest,
but also to assess the residual lung
and to look for any other abnormalities
that might be contraindications to surgery.
So here we're looking at patient with stomach, colon,
small bowel and kidney up in the chest,
but here's the normal lung on the contralateral side.
Now, liver position we of course can do with ultrasound.
We look for the vessels extending to the liver
and with some of our high resolution probes,
we can actually see the liver
parenchyma itself up in the chest.
But MR is really nice for showing the liver.
For example, here's a patient
with the liver in the abdomen
and the hernia up in the chest.
Looking at pulmonary hypoplasia,
we can trace out the lung on sequential images, add them up
and see how they compare to
what is normally expected in making a diagnosis
of pulmonary hypoplasia.
And then we can also do very specific techniques to look
for abnormal signal.
For example, if a patient has an abnormality such
as hemochromatosis here we're doing BOLD
or T two star imaging showing the darkening
that we get in the liver and in the spleen
with hemochromatosis.

Midline Abnormalities

I really like MR for looking at midline abnormalities.
For example here, gorgeous corpus callosum,
gorgeous vermis of the cerebellum.
And here we're actually looking at the palate
and it's very nice if you're thinking that there might be
a cleft palate, cleft soft palate in associated
with cleft lip in order to look.
And in a case such as this where there's micrognathia,
so the chin is small, these patients are really at risk
for a cleft palate without cleft lip.
So that because of the small chin, the tongue is high up,
it's hard to see here.
So we do multiple images till we get the fetus to swallow,
and then we can see there's a high riding tongue
and you don't have that normal dark band
of the palate coming across.
So in this case, again, multiple images in the midline are
how you're gonna make that diagnosis outside of the brain.
I think the next best reason to do an MR is
to assess the neck when there's an airway problem.
This is how we can really save lives.
When you're planning for delivery, can the baby be born by a vaginal delivery?
Does there need to be a C-section?
What about that EXIT procedure,
the ex utero intrapartum treatment procedure?
Or what about an EXIT directly to ECMO,
extra corporeal membrane oxygenation?
There's multiple small case series that show the benefit of MR in these cases
and there's no doubt
that MR plays a role in surgical planning.
Here, for example, we're seeing a large neck mass impinging on the airway.
Here's an example of one of the fetuses that went directly from EXIT to ECMO because of a mass right at the carina.
And you can see this is still a fetus still attached
to the umbilical cord
and they're looking down the trachea here to see
where the obstruction is.
This is a little bit of the uterus and
the maternal fat in the abdomen.
So for neck and MR for chest
and neck MRI, we use it to counsel patients to plan
for surgery and for airway management and delivery.
Here's an example of fetus with a great big teratoma.
You can see it in the it's an oropharyngeal teratoma.
It's in the airway here in the oropharynx extending out
into the amniotic fluid.
But look at that beautiful trachea.
So you can imagine a delivery.
The plan is to do a tracheostomy before clamping the cord.
So this is an EXIT to tracheostomy plan.

Resources for Fetal MRI

If you're starting to do fetal MRI I have a
website that's freely available.
BIDMC stands for Beth Israel Deaconess Medical Center.harvard.edu/fetal
atlas with a slash at the end.
And it shows a lot of nice, normal
and abnormal anatomy which can be helpful since obviously the appearance
of the fetus can be different than that which you're used
to either on ultrasound or an MR in neonates.

Summary and Conclusion

So in summary, it is not ultrasound versus MRI.
This is not a battle. I am an ultrasound person first.
It's how we can use the two of these modalities
to complement each other to best care for our patients.
So we use fetal MRI
as correlative imaging when ultrasound is inconclusive
and it's a really exciting field for clinical research.
So in conclusion, ultrasound will continue
to be the screening modality
of choice in evaluation of pregnant patients.
It's relatively low cost and it's real time,
but as our experience
with fast MR techniques increases will continue
to identify cases in which MR can aid in patient care.
Thank you.