Introduction to Pediatric Chest Radiography, by Dr. George Taylor.
Hello.
My name is George Taylor.
I'm from the Department of Radiology in Boston Children's Hospital.
And today, I wanted to talk about an introduction to the interpretation of the pediatric chest
x-ray with a special focus on how children are different than adults and trying a systematic
approach to the evaluation of the pediatric chest.
Now why are kids so different than adults?
Well, besides the tremendous size differences that happen with maturation, there is also
a tremendous change in the body of the child.
And those developmental changes are reflected on the pediatric chest x-ray.
For example, a normal two-month-old would have a relatively large thymus in proportion
to the chest.
And it can take almost half of the hemithorax and still be normal.
On the other hand, by seven months of age, the thymus has become much smaller in proportion
to the chest x-ray.
And by 16 years of age, you can hardly see the normal thymus.
And so if you have a 16-year-old with a large anterior mediastinal mass, such as the x-ray
on the screen, in a child who has neurofibromatosis, this would be highly abnormal at that age
and not quite as abnormal in a two-month-old.
So let's start with a systematic approach to the chest x-ray.
We will look at the lung parenchyma, the pulmonary vasculature, the airway and mediastinum, the
heart, and the bony abnormalities as well.
Lung parenchyma and vasculature.
Let's start with the lungs.
The factors that affect lung density are primarily pulmonary inflation, the pulmonary vascularity,
the lung parenchyma itself, and then overlying pleural air or fluid.
Here is a 14-month-old who presents with cough and wheezing.
And the initial frontal chest x-ray shows diffuse hazy opacification of both lungs that
may mimic an overwhelming pneumonia.
But you'll notice that there are only seven posterior ribs of inflation.
A radiograph obtained two minutes later shows a marked improvement in the opacification
of both lungs.
And so you can see that pulmonary hypoinflation can markedly change how the lungs look, especially
in a younger baby.
Here a two-year-old who presents with new onset stridor.
We can see an asymmetry in the density of the lungs, with the left hemithorax actually
looking much more lucent than the right side.
And if you notice also, the size of the pulmonary vessels is very different on the left side--
lower-- compared to the normal right side.
This is a child who aspirated a foreign body in the left bronchus with air trapping and
overinflation of the left lung and associated decreased pulmonary vascularity.
So asymmetry is an important thing to look for in the pediatric lung.
Here are two other conditions, two other situations where the hemithorax can look much more lucent.
Both of these infants have a pneumothorax.
The infant on the left side of the screen has a medial and anterior pneumothorax.
And the infant on the right side of the screen has primarily a medial pneumothorax.
Unlike adults, where the pneumothorax occurs more laterally to the lungs, infants tend
to collect pleural air in the medial and anterior location.
Because they are almost always in supine position.
And the lungs are relatively stiff, allowing them only to fall backwards, rather than recoil
to the center in towards the mediastinum.
Now focal parenchymal abnormalities are also very important in pediatrics.
This seven-year-old presenting with cough and fever has a retrocardiac density that
is also seen overlying the spine.
This is a round pneumonia, which is a bacterial pneumonia that happens almost exclusively
in children less than five years of age where the pneumonia is mass-like in appearance because
of poor development of the collateral air passages.
And so the pneumonia can look very much like a mass unlike that in adults.
Here another child who presents with cough and fever and has a right sided pneumonia.
We can see that the lung density is markedly different on the right side compared to the
left.
In this situation, we see that the lung can only be seen in the medial aspect of the right
hemithorax.
And pleural fluid is accounting for the density lateral to the chest.
And on the lateral film, we can only see one hemidiaphragm, suggesting that this child
has a pleural effusion in addition to the pneumonia.
Airway and Mediastinum.
Now let's consider the airway.
We need to look at its position, its caliber, and the possibility of displacement of the
airway by abnormal structures.
It's very important to know that the airway in a young child and infant is very mobile,
and during expiration, the trachea can buckle almost to 90 degrees, as you can see on the
frontal and on the lateral view in a normal expiratory radiograph.
The other two features to consider in the trachea are that one should see the tracheal
air column on the frontal view from the thoracic inlet all the way to the bifurcation of the
trachea.
And on the lateral, the course of the trachea should be a nice gentle posterior curve that
mimics the vertebral bodies of the thorax.
Here is a child where these features are not present.
This two-year-old presents with new onset wheezing, and immediately we see that the
mediastinum is much too wide for a two-year-old.
If you remember the first images that we showed, the thymus in a normal child at this age should
be much, much smaller.
So this is a wide mediastinum that is abnormal.
The second feature is that we cannot see the air column of the trachea on the frontal film
all the way to the bronchi.
We lose it in the mid portion of the chest.
On the lateral view, we can see that the trachea not only is markedly narrowed at the thoracic
inlet, but it is also anteriorly displaced by a posterior structure.
So in this situation, we have to think about things that live normally behind the trachea.
And these would be the esophagus, and/or lymph nodes.
So because this happened so acutely, we can-- we're concerned about an ingested foreign
body with an abscess.
Well, so we did an upper GI and barium swallow showing that this child had ingested a sharp,
plastic foreign body that had caused perforation of the esophagus, and a periesophageal abscess
that was anteriorly displacing and compressing the trachea.
So foreign bodies are an absolute must to consider in the appropriate age group between,
oh, 6 months to about 2, 2 1/2 years of age.
Here's another child that presents with an airway abnormality.
You can see that the trachea, rather than being slightly to the right of midline, it
is to the left of midline.
Normally, the aorta being on the left side minimally displaces the trachea to the right
side.
In this child, we see a right aortic arch and mild narrowing of the trachea.
This situation can be associated with asymptomatic right aortic arch and a vascular ring.
A CT scan in this child shows the normal caliber trachea in the upper image and moderate narrowing
of the trachea in the lower image, caused by a right aortic arch and the aberrant left
subclavian artery compressing the trachea posteriorly.
The other part of the mediastinum that is very important to evaluate in children is
the thymus and the possibility of adenopathy.
As we've seen before, the thymus can vary dramatically in size with age, and adenopathy
in children is much more commonly caused by inflammatory or infectious causes than in
adults.
Here, we have a two-month-old who presents with cough, and has a large anterior mediastinal
mass.
But if we look at it more carefully on the frontal film, we can see through the mass
on the right side, being able to see normal pulmonary markings behind it.
And on the lateral film, we can see a normal trachea with a normal caliber and filling
in of the retrosternal airspace.
On closer inspection of the left chest, we can see a scalloped appearance of this anterior
medialstinal mass, and the scalloping occurs every time an anterior rib crosses it.
And this is very characteristic of a normal thymus, which is very fatty and gets displaced
by normal structures.
Now, these next four images that I will show are all children that present with the right
upper lobe opacity, and we will go through the differences between a normal structure
and those that are pathologic.
The image on the left side of the screen, we've seen before and is a normal thymus.
The features of it are that we can see a nice, sharp inferior border, with no atelectasis
of the lung inferior to it or behind it.
We can see through it, and see normal pulmonary structures behind it.
And if you notice the trachea, it is not displaced or compressed by this normal thymus.
On the other hand, on the right side, we have a much denser mass that is adjacent to the
minor fissure of the right lung.
We can see a very sharp border, and we cannot see any lung markings behind it.
And the trachea is slightly displaced towards this child.
This is a child with pneumonia, and on occasion, we will be able to see air bronchograms in
the very dense area of a pacified lung.
This second pair, we have a right upper lobe density in the chest X-ray on the left side
of the screen.
But unlike the other two, there is elevation of the minor fissure, as shown by the arrow,
and we can see patchy air bronchograms of that right upper lobe, and also association
of the trachea being displaced towards this lesion.
This is right upper lobe atelectasis.
And the final case, we see a nodular density in the right upper lobe with displacement
of the trachea away from the mass, and a relatively dense-appearing mass.
This child has a neuroblastoma.
So I've shown four different right upper lobe lesions that have different characteristics
that can help us distinguish from the other.
Heart.
Now let's look at the heart.
We often talk about a normal cardiothymic silhouette in children rather than a cardiac
silhouette because the thymus can be so large that it will encompass the heart and go all
the way down to the diaphragms.
So the shadow of the heart, especially in young children, is composed of both the heart
and the thymus.
It is very difficult in young children to determine specific chamber enlargement because
the heart is relatively large in proportion to the surrounding chest.
And finally, we have a normal double atrial shadow is a normal finding rather than an
abnormal finding in adults.
Here we have a five-year-old girl who presents with cough and has a prominent left atrial
shadow, shown by the arrows.
This is a totally normal finding in comparison to adults, where the prominence of the left
atrial shadow can be a pathologic finding.
Bony Abnormalities.
Finally, a look at the skeletal system is very important when looking at a chest x-ray,
especially if we're looking at fractures for erosions and absence of normal bony structures.
Here, we have a nine-month-old who fell from her bed.
And initially the heart looks normal.
The trachea and mediastinum are normal.
And yet, when we look at the left sided ribs, we can see that there are multiple posterolateral
rib fractures as shown by the arrows.
Posterior and lateral rib fractures in infants below six months of age are very concerning
for non-accidental trauma.
So these are very important findings to make on the chest x-ray and often require oblique
images for better evaluation.
Here, another child who presents at two years of age with irritability.
We see what appears to be initially a normal chest x-ray.
But if we pay more attention to the right 11th rib, we see that the rib density is a
modeled and irregular and different from the other ribs.
Here, a close up of that rib shows a rib that is sclerotic and eroded by an overlying neuroblastoma.
So these are very important but often subtle findings in the pediatric chest.
So we've covered a systematic approach to the chest in children where we look at the
lung parenchyma, the pulmonary vasculature, the airway and mediastinum, the heart, and
bony abnormalities.
These are some final take home points that I would like to leave you with.
First, look at the symmetry of the lungs for density and for pulmonary vascularity.
Second, make sure you look at the lung behind the heart because it's a favorite place for
pneumonias to hide.
Make sure you look at the size in the position of the trachea, the bones, and soft tissues.
And finally, ask for help if you have any concerns at all.
Thank you.
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