Prenatal Diagnosis of Skeletal Abnormalities - 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 am gonna be talking about ultrasound
of skeletal abnormalities.
Hello, today I am gonna be talking about prenatal diagnosis
of skeletal abnormalities.

Short Humerus and Short Femur

Now, when we do obstetric ultrasound,
probably the most common thing that we'll see is a short,
humorous or short femur.
So I'll be talking about those particularly
with respect to down syndrome.
But then I'll also be talking about abnormalities such
as polydactyly, scoliosis, amputations
and amniotic band syndrome, scro, coogal teratoma,
positional deformities, for example,
club feet and clenched fists.
And then finally skeletal dysplasias.
So let's start with the short humerus and short femur.
These are both sonographic features
of Trisomy 21 or Down Syndrome.
And there are many different definitions for
what comprises one of these short, so-called long bones.
It can be based on the observed over expected length.
It can be less than the fifth percentile for gestational age
or less than some number, usually
around 0.9 multiples of the median.
When you get one of these numbers,
you take a patient's pretest probability
and look at the likelihood ratio of down syndrome.
And it turns out that that likelihood ratio is higher when
there's an abnormal femur uh,
humeral length than when there's an abnormal femur length.

Likelihood Ratios

Alright, so when we look at likelihood ratios
and there have been a number of different studies,
I just have four of them up on this slide.
You can see that there are a number
of different likelihood ratios for abnormalities
that we might see in the second trimester.
For example, nuchal thickening has a likelihood ratio
that's very high, um, as does echogenic bowel,
but short humerus
and short femur are much lower as low as only 1.2 and
therefore, um, these aren't very strong predictors
of down syndrome.
Another problem is that the false positive rate,
for example, with a short femur is as high as 20%.
And you can imagine there are some populations of people
that are just normally shorter than others.
For example, the Asian population,
you really can't use a short femur length.
Now it turns out that there's some hints we can use when we
look at the dating sheet
to figure out if a short femur is important or not.
For example, in this particular patient,
the femur is measuring 19 weeks, five days, um,
and the bial diameter 21 weeks, two days.
The age by is 20 weeks, six days.
And it turns out that in down syndrome they tend
to have a slightly rounder head, meaning a bigger BPD
and again the short femur.

Recommendations

So what are our recommendations if we see a short,
humorous or short femur?
Well, if it's isolated, if other testing is negative
and if the pretest probability is low,
these it can likely be ignored.
When you see a shortened bone though, you wanna make sure
that it looks morphologically normal.
And so you look at the morphology
and then you need to remember
that a shortened long bone could indicate uh,
fetal growth abnormality.
Um, and so you're probably gonna get follow-up
later on in gestation.
There's been an increase in intrauterine growth restriction
that's been noted following an isolated short femur
or short humerus and
therefore it's reasonable
to get one follow-up ultrasound in the third trimester.

Example with Hydrops

Alright, now here's a patient who had a short femur
and also has hydro drops.
I say there's hydro drops
'cause there's skin thickening, there's a pleural effusion
and there's also this abnormality
that we see pooching out just
above the Accord insertion site of big em falle.
And here's her short femur.
14 weeks age by date is 16 weeks.
The abdomen here is measuring fairly large
because again of that all that soft tissue edema.
So this kind of finding when there's a short femur
and other abnormalities should really, really make you think
of a chromosome problem.
And here you can see that there's a cystic hydroma,
big ated fluid collection behind the neck,
even extending down the back.
So we're gonna think about a chromosome abnormality
in a patient like this.
Well, let's now move on past the short humerus
and short femur and go to polydactyly.

Polydactyly

Polydactyly is when there are too many digits
and usually instead of five digits on an extremity,
there'll be six, although you could have more.
So here we can count, there's a thumb one
and there's the second, third, fourth, fifth,
and here's a sixth digit.
Now 3D ultrasound can be helpful, uh, to look at this, uh,
but basically you need a good 2D picture in order
to get a good 3D picture.
And here's a postnatal radiograph showing you
that sometimes this extra digit is not completely formed.
Sometimes it doesn't even have bone within it.
And this also tells you that it can be fairly easy to remove
after a baby is born.
Um, the surgeons can just so-called lop off
that little extra digit.
Uh, but what's important is to figure out the familial, um,
recurrence of this, the familial incidents,
and also know about the syndromes that can happen with this.
So you need to figure out which side
of the hand this extra digit is on.
Is it on the thumb side or is it on the ulnar side?
Pre axial is the thumb side that's usually sporadic.
And post axial is on the ulnar side
and that's usually either familial or syndromic.
So if you see that extra digit,
you figure out which side it's on.
You talk to the parents about whether there's any family
history of extra digits.

Scoliosis

Well, our next main topic is scoliosis.
And scoliosis is when there's a bend in the spine.
And usually if we can see this prenatally,
it's a fairly severe scoliosis.
You're first gonna think about a vertebral abnormality
and if there is a vertebral abnormality, you'll think
of the the Vader Association.
And that stands for vertebral a**l rectal,
cardiac tracheal esophageal fistula, uh,
radial ray anomalies, um, and limb reia.
Sometimes uh, people put chromosomal abnormalities in
that V association as well.
You can also see scoliosis with neural tube defects
and you can also see it with amniotic band syndrome.
So you wanna look very carefully at basically the entire
fetus whenever you see an abnormal bend in the spine.
So here for example, we have a fetus
with a really acute angle scoliosis,
you count which lumbar vertebral body it's at,
and in this case it's at about L three
and there were splaying of the, uh,
posterior vertebral elements.
You can see this here, um, that will make you think
of a neural tube defect, but we didn't see any sac here.
Now, not all neural tube defects need to have a sac
and you can clearly see here
that these bones are extending right out
to the skin on this 3D reconstruction.
And this was indeed a neural tube defect.
Now here's a very, very curved spine.
No normal fetus would have a spine curving
side to side like this.
In fact, we're getting an image of both the chest
and the abdomen in the same image.
That's how curled up this fetus was.
And you could actually see unattached amnion here.
So this is a classic example of amniotic band syndrome,
but the really severe form of amniotic band syndrome,
which is also called limb body wall complex.
When you have limb body wall complex,
you might have a head abnormality such as anencephaly
or an encephalocele,
and these won't be your usual midline cephas.
These will be off midline.
You might see facial clefts,
you might see breaks in the abdominal wall
or the thoracic wall, the so-called thoraco schisis
or abdominal schisis.
You can see limb defects, scoliosis.
And because the fetus can't move normally you get a
short umbilical cord.

Amniotic Band Syndrome

Now this is very different,
the limb body wall complex from a more isolated amniotic
band syndrome where you have limb reduction defects.
And here for example, we're looking at an upper extremity
and it comes to an abrupt halt
and you're not seeing a hand at the end of this extremity.
And the long bones when you measure them are slightly short.
Here we can see a fetus with amniotic band syndrome
where one hand looks normal and you can see an open hand
and the fingers spread out here.
But the other hand you can see one
of these limb reduction defects with an absent hand.
Sometimes you'll just see a shortened um, humerus.
For example, here the humerus just abruptly ends.
It's too short and you can see the defect in the skin here.
And you can almost imagine what's happened here in
that an amniotic band has been tightened
around an extremity.
Here it's cut off the blood flow
and the more distal extremity has just kind of melted away.
Sometimes you'll actually see that band.
And here we can actually see that band
of tissue going across these, uh, this lower extremity.
So this is the more proximal portion of the extremity.
This is the distal portion.
And you can imagine the arterial flow was coming in,
the venous flow couldn't get out,
so the tissue distally becomes very emus
before it kind of melts away.
And you can actually see the kink in this long bone, um,
from that constricting band.
Well, the next topic
after amniotic band syndrome is sacro teratoma.

Sacrococcygeal Teratoma

Of course, we wanna differentiate a sacro
teratoma from a neural tube defect.
And the big difference is that when you look at the spine,
the spine posterior elements are normal.
Sometimes if a sacro cog teratoma is large enough,
it will actually push up against the vertebral bodies
and make the anterior portion of the spine be deformed.
Here we're seeing a large cystic sacral co geo
teratoma here.
We're seeing one that's both cystic and solid.
And it's really important when you see one
of these masses at the base of the spine that you look for
how many internal organs are affected.
Is there any obstruction, for example, of the bladder
or of the GI tract, but also how vascular is it?
Because it's the amount of vascularity
that will determine whether a fetus is at risk
for developing hydro drops.
And here we can see on this color doppler
and pulse doppler that there's a little bit of blood flow in
that solid element, but not much.
Now it can be very, very hard to tell how much
of these sacrococcygeal teratomas are actually intra pelvic
in the pelvis itself.
And that makes a difference for how we counsel the patient
as far as the surgery and the expected outcome postnatally.
So in those cases it can be very helpful to get an MRI.
And here we've got an MRI, um, showing the spine.
Here's the thecal sac
and here's the sal Teratoma
with just a very small part extending into the pelvis.
Now when these teratomas are predominantly solid
and very, very vascular, um,
that's when they can cause hydro drops
and they can also cause the mirror syndrome, um,
where the mother gets ill as well as the fetus
because of the hydro drops.
Here's a classic diagram for how we grade these different
sidal teratomas, depending on their intra pelvic extent.
Um, this is described in pediatric patients,
but it's the same description, um, that we use in the, uh,
fetuses as well.
Well, let's now move on to positional deformities.

Positional Deformities

And when you can get a beautiful hand like this waving,
hello, it's very reassuring, uh, both to the parents
and to the sonographer, um, that the hand is there
and that the digits are there
and that the fetus is moving normally.
Of course, you wanna see both hands on both sides, uh,
looking normal like that.
Um, similarly, a normal view
of the feet is when you can get this hang 10 appearance.
If you can get the bottoms of both feet lining up like this
and see all 10 toes, then you know
that there's not a positional deformity of the feet.
It just wouldn't be able to look like that.
So those are very reassuring signs.
Um, in contradistinction to this is the clenched fist
and the clenched fist is classically seen.
Um, in trisomy 18 here you can see a fetus also has
ventricular magaly.
Um, but these clenched fists, we can't even show
how we would hold a fist in this position
because not only are the fists, um, closely tightened,
but they also have overlapping um, digits.
As you can see here, rocker bottom feet are harder to, uh,
illustrate sonographic.
So instead I have this image, um, that was
taken from Dr.
Chadley from the Department of Pediatrics
and Child Health at the University of Manitoba.
And it shows you the nice rocker bottom feet
that you'll see in a fetus with trisomy 18.
So here are the findings in tri 18.
There's a great big laundry list of findings.
Um, second trimester growth restriction, polyhydramnios,
heart disease, hernia, phae,
but it's the limb malformations that I'm talking about here,
clubfoot rocker, bottom foot art grippo, which is where the,
uh, extremities are just held at an awkward angle, um, the
and don't move normally,
and then the clenched hands with the overlapping digits.

Clubfoot

Now when we see a clubfoot, there are a lot
of different things that we'll think about.
Clubfoot neural tube defect should jump to mind.
You wanna do a good job looking at the spine
and at the posterior fossa,
but it's another one of those abnormalities
where you might wanna get a family history
because sometimes there'll be a family history of clubfoot
and the parents will very well know
that either it's easily correctable
or they had to wear a brace for a while in childhood.
You wanna look very carefully at all of the brain, um,
since brain abnormalities are associated with clubfoot,
but realize sometimes there can be a positional deformity,
especially if there's oligohydramnios.
Now in this case, the fluid is normal,
the foot is up against the edge of the uterus,
you'd wanna move, uh, the pregnant woman around
and make sure that no matter how she's turned
and where this lower extremity is,
that the foot is constantly held in that abnormal position.
Here are two more examples of club feet.
Now some people really like 3D um, ultrasound
to demonstrate these abnormalities,
but again, you have to first see it in 2D to understand
that the abnormality is actually present, um,
before these re uh,
3D reconstructions can really be helpful.
But here, when you have abnormal positioning,
and this is getting to that arthrogryposis type of case, um,
again, the 3D can be very helpful.
It can be sometimes difficult
to get an entire extremity on a single 2D view.
And when you get that 3D it, it can really be helpful.
And in a case like this, it really helps you
understand the anatomy better.
You've got kind of a for shortened humorous,
definitely radius and ulnar almost absent.
And then you've got these hands held at an awkward angle.
This is a very unusual position
and it should really make you think of a syndrome
and not just one of these amniotic band syndromes.
It's not just a reduction defect.
This is something more than that.
This is both a reduction defect and abnormal positioning.
And the thing to think about there is Holt Orum syndrome.
Now when we're talking about skeletal abnormalities, many
of these different appearances will have many different
potential etiologies,
but looking for the associated abnormalities can be helpful.
For example, in Holt Orum syndrome, um,
there frequently is congenital heart disease, A-S-D-V-S-D,
endocardial cushion defect.
But you can also have these abnormalities of the upper limb,
folia, radial radio hyperplasia, a phalangeal thumb
and clinodactyly, which brings us to
what you probably thought this whole talk was about
skeletal dysplasias.

Skeletal Dysplasias

When we talk about abnormalities of the skeletal system,
that's what people first jump to.
But actually many of these other abnormalities,
the positional deformities, the short humerus,
short femur are much,
much more common than these skeletal dysplasias.
So you always wanna make sure, um,
that you look at the long bones, see what they look like,
see if they look morphologically normal
before you jump to a skeletal dysplasia.
Prenatal diagnosis is very, very difficult
for skeletal dysplasias.
There's 150,
probably even more different skeletal dysplasias.
And we can actually do, um, some genetic testing for some
of these, particularly if patients have a known family
history with a known genital, uh, congenital abnormality,
um, that can be tested for with genetics.
So frequently there's molecular testing available, um,
and it can also be helpful to plan delivery.
It's also important when you diagnose a skeletal dysplasia
to have a complete evaluation at birth.
And, um, if a family is planning to terminate
and if it's gonna make a difference in a future plan, uh,
pregnancy, then you can actually do some tissue sampling,
uh, for testing and accurate
counseling for recurrence risks.

Thanatophoric Dysplasia

So let's look at a classic skeletal abnormality.
The patient comes in
and her age by date says 20 weeks, three days.
Look at this BPD, 22 weeks, three days.
So the BPD, again, it's a round head, it's too big, um,
and very, very short femur, 14 weeks.
This is not the slightly short femur
that you see with down syndrome.
This is a severely short femur.
And because it's so short, so early, all
of those other abnormalities that I kind of say,
well just check growth later, they all disappear.
This is going to be a skeletal dysplasia,
it's just way too short, way too early.
So you look at these long bones and they're very, very short
and you know that this is severe micro meia.
You look at the head and it's very, very round.
Now there's some other findings
that can be a little bit more difficult.
One of those is this very wide iliac angle.
Normally when you're looking at the distal spine,
you can see these nice posterior elements pointing
to towards each other here,
but you don't have those iliac wings
so widely splayed apart.
But what's really important when you see one of these early,
early, um, severe abnormalities is
to look at the chest size.
Because even if we have trouble figuring out exactly
what the prenatal diagnosis is, figuring out if it's lethal
or not is gonna be very, very helpful in counseling.
And the lethal dysplasias are those
that have a small chest size.
So here we are at only 20 weeks.
Um, the thoracic circumference is the fifth percentile
for gestational age, and these ribs are very short
and a lot of these, uh, skeletal abnormalities
that are lethal do have short ribs
and do have a very, very small chest.
And so, um, you can imagine if a baby were to be born
with this abnormality
that the baby would've difficulty breathing
because the lungs haven't had enough room to grow.
Normally you can actually see
that there's skin thickening here as well.
Less important, but a nice illustration here are
these short stubby fingers.
So I've shown you a lot of images in this case
and just give you a second to think about.
We've got kind of a round head.
We've got a very, very small chest.
We've got very, very short long bones
that are obvious early in gestation.
And the classic diagnosis is thanatophoric dysplasia,
the death loving dysplasia.
And this is important again
because it's a lethal skeletal dysplasia.
And I've got images from another fetus here
with the same diagnosis.
The recurrence risk, it's nice to know, uh,
for when you're talking to parents,
is not significantly higher than the general population.
And if you're in a location where you can have DNA, uh,
based prenatal diagnosis, you can definitely offer that.
So here's another case. You've got the short ribs here.
We've got the so-called telephone receiver, um, femur, um,
where it's short and stubby,
but it's got the flared metaphysis.
Um, and on this image you can see the short
ribs and the skin thickening.
Um, here's an image of a neonate
with the thanatophoric dysplasia.
Again, you can see, um, the big head
and the very, very small chest and the short long bones.
Um, the incidences, it depends if you're counting in utero
or uh, postnatal, maybe about one in, uh, 8,900, uh,
classically described as having that prominent forehead
and the depressed nasal uh, bridge.
There's a long differential diagnosis.
Um, and basically knowing every one
of these different things is not as important as looking
and assessing for that lung size
and saying that this is a lethal abnormality.
So here for example, as a chest x-ray of a neonate
with thanatophoric dysplasia, see the small chest,
see all the skin thickening,
and obviously, uh, this baby died.
Um, there's no aeration in the chest at all.
Here's that classic telephone receiver femur.
Um, and that's the type one thanatophoric dysplasia.
What a lot of people don't recognize is
that there's a type two thanatophoric dysplasia
where the femur is straight
and then you might get the clover leaf skull.

Heterozygous Achondroplasia

Well, let's move on now to heterozygous achondroplasia.
And it turns out that of the, the neonates
that survive when they're diagnosed in utero, those
that survive, this is gonna be the common one.
This is the dwarf that you might see walking around.
So here's um, an example of a case.
A fetal survey was normal at 21 weeks, totally normal.
And additional imaging was requested at 30 weeks.
So here's the date sheet at, um, 21 weeks age
by ultrasound was 20 weeks.
All of these parameters are right about 20 weeks,
so she's just off by a week and that's basically normal.
There's no problem with that.
Um, you look at 31 weeks
and here's a femur, it's still straight,
but it's now starting to drop off the growth curve.
If you look at this date here, it's 27 weeks, six days,
whereas your age by dates is 31 weeks, five days.
So it's now about four weeks behind.
And this is pretty classic for thanatophoric dys, uh,
I'm sorry for heterozygous alaia
where it looks normal early
and starts to drop off the growth curve at about 27 weeks.
You look at the chest here and the chest size is normal.
There was polyhydramnios
and another finding was nicely shown
because of the polyhydramnios,
the so-called trident fingers.
I would never use Trident fingers to make the diagnosis
of heterozygous achondroplasia,
but it's an ancillary finding.
And then you've also got the so-called frontal bossing.
Um, and here you can see a little bit
of the prominent forehead here
and here with the polyhydramnios.
Now I don't do a lot of plain film in pregnancy.
They used to do a lot more of it.
Um, you can do it to look at the um, shape
of the long bones, but really we don't want
to expose neonates to um, or fetuses to ionizing radiation.
So this is infrequently done, um, prenatally,
although definitely after the babies are born, um,
they might do that to help establish a diagnosis.
But this is, um, nice to show
what you might see if a radiograph were done.
Uh, narrow thax with short ribs.
Um, another radiographic finding is the short skull base.
You can have the small square iliac wings,
posterior scalloping of the vertebral bodies.
It turns out that the intraocular distance
of the lumbar spine of vertebral bodies decreases from L one
to L five instead of, um, the normal increase.
And that's why, um, these children
and then adults, uh,
can often have spinal stenosis later in life.
Here's an example of this neonate.
Um, the same one I showed you
before with the si kind of round rounder head, uh,
the frontal bossing the trident hands
and they'll also have those widely spaced nipples.

Osteogenesis Imperfecta and Hypophosphatasia

Well, here's another case
and this one I'll be showing you is a little bit
of an unknown, really,
really severe micro meia showing up at a very
early gestational age.
In this case, the gestational age is 17 weeks.
The femur length is measuring 13 weeks.
So it's an early diagnosis.
It's hard to even tell that that's a femur length.
Really, really hard to see.
When you look up at the head there's
decreased mineralization.
And this is a really important finding.
How do I know there's decreased mineralization?
Where normally it's pretty darn easy to see the downside.
Choroid plexus and ventricle, it's harder
to see the upside choroid plexus and ventricle.
And that's because normally the skull is ossified
and you get shadowing behind the ossified skull.
But here we're seeing both sides of the brain equally.
Well, that's how we know it's a demineralized skull.
So here we're seeing the um, skull all the way around,
but it's not ossified beautiful.
Look at the intracranial anatomy.
We look at the chest and it's a little bit small
and look at these ribs, they're bent.
And here when we look at the ribs, they have kind
of a wavy appearance.
So think about it, what's your differential diagnosis?
There's very, very severe micro meia
and there's poor ossification.
There's really only two things we think about in this
instance, osteogenesis imperfect as the one
that first pops into mind and then hypophosphatasia.
And the reason it's important to think about both of those
is that osteogenesis imperfecta has a five
to 7% recurrence risk.
It's not just that it is genetically inherited,
but they're also phenotypic differences.
Hypophosphatasia autosomal recessive has a
25% recurrence risk.
However, either way, as an ultrasound person, uh,
you're gonna recommend that in the next pregnancy, um,
that the patient gets screened early on.
So here's a case 23 weeks with short long bones
and we can see broken bones everywhere,
really classic broken bones here, here you can see a bone
that looks straight and then you see the break
and another broken bone right here.
Um, by date she's 23 weeks.
Her femur length because
of these breaks is measuring 20 weeks.
You look at the chest and you see all
of these broken bones look at the ribs,
broken bones everywhere, very wavy appearance of the ribs.
And when you look at this chest, you can see how deformed
and abnormal it is because of all the broken bones.
But when you look up at the head,
the ossification doesn't look as bad as
that prior case that I showed you.
And again, that's because of the phenotypic differences.
You can still have osteogenesis imperfecta
and still have some ossification.
Um, but just a, a different kind of appearance
and a different time of presentation
of all of the broken bones.
But again, this is osteogenesis type two
and the thoracic circumference in this case was small.
Here's a different case of osteogenesis imperfect.
And again, you can see that um, this
fetus then neonate did not survive.
We're not seeing, um, aeration in the lungs.
The bones are all uh, broken.
The ribs are broken, multiple fractures seen in the long
bones that are very deformed.
Now there are many different types
of osteogenesis imperfecta
and personally I don't think the different types are
that important to know.
Um, but, but some understanding of the presentation
and the phenotypic variability is important to know about
the, the type one might be born
and not have fractures
until later on in life when they just have easier than
normal fractures, they can actually have normal stature.
The type four is also a milder form, short stature, um,
and variable age of onset.
The type that we tend to see in utero is the type two when
we have that extreme, um, bone fragility leading
to either intrauterine or very early, um, infant death.
So here we've got an example of a plain film, um, of a fetus
who did not survive with osteogenesis imperfecta.
And again, you can see the very, very short long bones
and the poor ossification of the skull
and the very, very small chest.

Other Dysplasias

Well, just because a bone looks bent
doesn't mean it's broken
and doesn't mean it's osteogenesis imperfecta.
And I had to learn this the hard way.
Um, here we've got what looks like a bent bone, um,
in a fetus that ended up being diagnosed
with campic dysplasia.
So just be a little bit careful about
how definitively you make these diagnoses.
In campic dysplasia,
though you won't see broken bones everywhere, um, you tend
to see this appearance in the femur.
Another abnormality
that can be diagnosed in utero is a androgenesis.
And here I've got a case of agenesis.
We're looking at normal ossification of the skull,
but we're seeing a large amount
of soft tissue in the nuchal region
with some fluid um, collection.
In this case, we're seeing a very, very small chest look at
how small these ribs are.
Um, the heart is big in the chest
and looks deformed as well.
Um, but there's very, very severe micro meia.
Look at how small these long bones are.
Very tough diagnosis to make in this case.
We would really end up saying that this is some type
of lethal skeletal dysplasia
and we're not quite sure what in this case.
We actually had to do a vaginal scan in order
to better define um, what bones we were seeing
and what bones we were not.
There was so much subcutaneous edema
and uh, this was a very early termination of pregnancy
because basically this was not going
to be compatible with life.
And here you can see that there's um, absent ossification
of the spine and pelvis bowing of the long bones
with metaphyseal cuffing.
So I've shown you probably too many skeletal dysplasias.
But what I'd like to leave you with is an idea
that there's lethal anomalies
and then there are anomalies
that can have variable outcomes.
So the lethal anomalies,
the thanatophoric dysplasia is gonna be the one we see most
commonly in utero, um, with an incidence
of about one in 10,000.
Agenesis is also autosomal recessive may be one in 40,000.
The osteogenesis type two I've shown you a lot of cases
and that's 'cause we can diagnose
that pretty easily when we see those
long bones that are broken.
Um, but the incidence it turns out is only about
one in 60,000.
Now heterozygous achondroplasia you might say, how come
that's the one I see most commonly walking around?
And the answer is
because that's the one that's compatible with life.
It's not one of these lethal skeletal dysplasias.
So I've shown you these
and I've shown you some ways that we can make the diagnosis
or at least suggest the diagnosis,
but I wanna tell you that we're not that accurate.
And if you look at a number of different studies,
they report accuracy in the range of about 50%.
And some of these accuracy values are important, um,
because they can be changes in the genetic counseling
after a final diagnosis.
So a study by Gafney in 1998 um, said
that, um, these abnormalities
and these changes in diagnoses were more frequent, um,
for thanatophoric dysplasia
and osteogenesis imperfecta, um, than for,
uh, specific features.
And that rare diagnosis, uh, were more likely to be accurate
and that in 20% of the time,
a specific diagnosis couldn't even be made postnatally
despite full pathology and an expert referral.
So you can imagine if 20%
of the time we can't make the diagnosis when we've got a
baby in front of us, uh, how much harder must
that be in utero?

Conclusion

So in conclusion, antenatal ultrasound is excellent
for discovering lethal skeletal dysplasias.
We look at the clinical exam, x-rays autopsy,
we have multidisciplinary postnatal assessment all being
important for our most accurate specific diagnosis.
And then, uh, if you're in an area where storage of tissue
and genetic testing is available, that's very important
for future testing for prior pregnancies.
Well, those are my conclusions for the skeletal dysplasias.
Um, but I also wanna just bring you back to
prenatal diagnosis of the skeletal dysplasias.
And there our first question is, is it lethal?
Look at the thoracic circumference
and look at the associated features such as hydro drops.
What about the pattern of the affected bones?
Is it everywhere or is there just a focal limb shortening?
And if there is some limb shortening, is it angulated?
And then remember that the final diagnosis might
but not be known until after birth
and that a specific diagnosis will aid
in genetic counseling.
Um, and that recurrence risks will change, um,
if your diagnosis changes in about 50% of the cases.
Thank you.