How to Interpret a Chest X-Ray (Lesson 5 - Cardiac Silhouette and Mediastinum)

Summary

This educational video, the fifth in a series on interpreting chest X-rays, focuses on analyzing the cardiac silhouette and mediastinum. It outlines how to assess these structures and recognize common abnormalities. The video clarifies the impact of PA and AP films on heart size perception and details specific cardiac conditions like cardiomegaly, left atrial enlargement, and pericardial effusions. It also discusses mediastinal regions, abnormalities like widened mediastinum and hilar enlargement, and uses the hilum overlay sign to differentiate hilar masses. The script provides a comprehensive guide for medical professionals to diagnose conditions affecting the heart and mediastinum.

Takeaways

• 📚 This video is part of a series on interpreting chest x-rays, focusing on the cardiac silhouette and mediastinum.
• 🔍 The learning objectives include assessing these structures on x-ray and recognizing common abnormalities.
• 🧠 It's crucial to remember the anatomy of the cardiac silhouette and mediastinum from lesson two.
• 📈 The video is divided into two halves: the first covers heart abnormalities, and the second covers abnormalities of the hila and mediastinum.
• 📎 A key difference between PA and AP films is highlighted, emphasizing that heart size is only accurately assessed on PA films.
• ❤️ Cardiomegaly, or an enlarged heart, is a common abnormality and can be quantified using the cardiothoracic ratio.
• 📏 Left atrial enlargement can be identified by splaying of the coronal angle beyond 90 degrees and the double density sign.
• 🫁 Right ventricular enlargement is indicated by filling of the retrosternal space on lateral views.
• 💧 Pericardial effusions can present as a large cardiac silhouette and may have a 'water-bottle' shape or 'Oreo cookie' sign.
• 🔍 Dextrocardia, a congenital anomaly, is mentioned as a rare condition where the heart is positioned opposite to normal.
• 🏥 A widened mediastinum can indicate mediastinal masses, which are categorized into anterior, middle, and posterior regions.

Q & A

What is the main topic of the fifth video in the series on interpreting chest x-rays?

The main topic of the fifth video is the cardiac silhouette and mediastinum, focusing on how to assess these structures on x-ray and understanding common abnormalities seen in them.

What is the importance of remembering the structures that comprise the cardiac silhouette?

Remembering the structures of the cardiac silhouette is important for accurately assessing abnormalities on x-rays, as these structures can indicate various cardiac conditions.

How does the divergence of x-ray beams affect the appearance of the heart on a PA film?

On a PA film, the divergence of x-ray beams does not significantly affect the heart's appearance because the heart is a relatively anterior structure and close to the film, so the shadow it casts is an accurate representation of its true size.

Why is the heart size on an AP film not as accurate as on a PA film?

The heart size on an AP film is less accurate because the greater separation between the heart and the film causes the diverging x-ray beams to create a larger shadow, exaggerating the size of the heart.

What is the definition of cardiomegaly in the context of chest x-rays?

Cardiomegaly is defined as the overall size of the heart being larger than normal, commonly assessed using the cardiothoracic ratio, which is the maximum horizontal cardiac width divided by the maximum horizontal thoracic width. Cardiomegaly is present if this ratio exceeds 50% on a PA film.

What is the cardiothoracic ratio and how is it measured?

The cardiothoracic ratio is the ratio of the maximum horizontal cardiac width to the maximum horizontal thoracic width, measured between the inner surfaces of the ribcage. A ratio exceeding 50% on a PA film indicates cardiomegaly.

What are the two cardiac chambers that can be individually identified as enlarged on an x-ray?

The two cardiac chambers that can be individually identified as enlarged on an x-ray are the left atrium and the right ventricle.

What is the 'double density sign' and what does it indicate?

The 'double density sign' is an x-ray finding where the left atrial enlargement causes a second shadow along the right heart border, indicating the left atrium is enlarged.

What is the significance of the 'Oreo cookie sign' in x-ray interpretation?

The 'Oreo cookie sign' is seen on lateral films and indicates a pericardial effusion. It consists of three layers: a radiolucent posterior layer (pericardial fat), a radiodense middle layer (effusion), and an anterior radiolucent layer (epicardial fat).

What is dextrocardia and how is it depicted on an x-ray?

Dextrocardia is a congenital anomaly where the heart loops around in the opposite direction during early embryologic development, resulting in the heart being on the right side of the chest instead of the left. On an x-ray, it appears as if the heart is reversed in orientation.

What is the definition of a widened mediastinum on an x-ray?

A widened mediastinum is generally defined as being greater than 8 centimeters on either a PA or an AP film. However, many cases of an apparently widened mediastinum are due to patient rotation, poor inspiratory effort, or an AP view.

What are the four regions of the mediastinum and what types of masses can be found in each?

The four regions of the mediastinum are the anterior, superior, middle, and posterior mediastinum. Masses in the anterior and superior mediastinum can include lymphoma, goiter, thymus tumors, and teratomas. Middle mediastinum masses can be lymphadenopathy, aortic aneurysm, pericardial cysts, dilated esophagus, or hiatal hernia. Posterior mediastinum masses typically include neurogenic tumors and spinal mass extensions.

Outlines

00:00

📚 Introduction to Cardiac Silhouette and Mediastinum

This paragraph introduces the fifth lesson in a series about interpreting chest X-rays, focusing on the cardiac silhouette and mediastinum. The lesson aims to teach how to assess these structures on X-ray and recognize common abnormalities. It reviews the anatomy of the cardiac silhouette and mediastinum, emphasizing the importance of remembering the structures that make up the silhouette. The video is divided into two halves: the first covers heart abnormalities, and the second covers abnormalities of the hila and the rest of the mediastinum. The paragraph also discusses the difference between PA and AP films, explaining how the diverging X-ray beams in PA films can affect the perceived size of the heart on the image.

05:01

🔍 Abnormalities of the Cardiac Silhouette

This paragraph delves into specific abnormalities of the cardiac silhouette, starting with cardiomegaly, which is an enlargement of the heart's overall size. The cardiothoracic ratio is introduced as a common way to define cardiomegaly on chest X-rays, with a ratio exceeding 50% on PA films indicating its presence. The ideologies of cardiomegaly are discussed, including left or right-sided heart failure. The paragraph also covers the identification of enlarged cardiac chambers, such as the left atrium and right ventricle, and their respective ideologies. Additionally, it touches on pericardial effusions, their appearances on X-ray, and the various causes of these effusions.

10:02

🧬 Congenital Anomaly and Mediastinal Abnormalities

The paragraph discusses a rare congenital anomaly called dextrocardia, where the heart loops abnormally during early development, resulting in the heart being on the right side of the chest. It then moves on to abnormalities of the mediastinum and hila, with a focus on a widened mediastinum, generally defined as greater than 8 centimeters. The four regions of the mediastinum are outlined, and the differential diagnosis for masses in these regions is discussed. Examples of masses in different mediastinal regions are provided, including a multinodular goiter and a pericardial cyst. The paragraph concludes with a discussion of the hilum overlay sign, which helps distinguish the location of a mass relative to the hilum.

15:03

🏥 Hilar Abnormalities and Differential Diagnosis

This paragraph focuses on abnormalities of the hila, such as bilateral hilar enlargement, which can be caused by a variety of conditions including malignancy, infection, and other diseases like sarcoidosis and silicosis. The differential diagnosis for hilar enlargement is broad and can include lung cancer, lymphoma, metastatic disease, tuberculosis, and viral infections, among others. The paragraph provides examples of hilar enlargement in patients with sarcoidosis and pulmonary hypertension. It also discusses the hilum overlay sign to differentiate hilar masses from those anterior or posterior to it, using an example of a saccular aortic aneurysm.

Keywords

💡Cardiac Silhouette

The cardiac silhouette refers to the outline of the heart as seen on an X-ray. It is a crucial element in interpreting chest X-rays, as it can reveal the size and shape of the heart, which are indicative of various cardiac conditions. In the video, the cardiac silhouette is discussed in the context of identifying abnormalities such as cardiomegaly, which is an enlargement of the heart.

💡Mediastinum

The mediastinum is the area between the lungs, containing the heart, large blood vessels, trachea, esophagus, and lymph nodes. It is a central focus in the video, as abnormalities in the mediastinum can indicate a variety of health issues, including tumors and infections. The video discusses how to identify and interpret abnormalities in the mediastinum.

💡Cardiomegaly

Cardiomegaly is a condition where the heart is enlarged, which can be identified by an increased cardiothoracic ratio on an X-ray. The video explains that cardiomegaly can result from various causes, including left or right-sided heart failure, and that it can be assessed using the cardiothoracic ratio.

💡Cardiothoracic Ratio

The cardiothoracic ratio is a measurement used to determine if the heart is enlarged by comparing the maximum width of the heart to the maximum width of the thoracic cavity on a PA chest X-ray. The video uses this ratio as a diagnostic tool, with a value over 50% indicating cardiomegaly.

💡Left Atrial Enlargement

Left atrial enlargement is a condition where the left atrium of the heart is larger than normal. The video describes specific X-ray findings that indicate this condition, such as splaying of the coronal angle and the double density sign, which are related to the left atrial enlargement.

💡Right Ventricular Enlargement

Right ventricular enlargement can be identified on an X-ray by the filling of the retrosternal space. The video explains that this condition can result from causes such as pulmonary hypertension and pulmonary valve disease.

💡Pericardial Effusion

A pericardial effusion is the accumulation of fluid around the heart. The video describes how this condition can appear on an X-ray, with a large cardiac silhouette and characteristic shapes like the 'water-bottle' or 'Oreo cookie' sign.

💡Dextrocardia

Dextrocardia is a congenital condition where the heart is positioned on the right side of the chest instead of the left. The video mentions this anomaly as an example of a condition that can be identified on an X-ray, even though it is relatively rare.

💡Mediastinal Masses

Mediastinal masses are tumors or growths that occur within the mediastinum. The video discusses how to identify these masses on X-rays and differentiates them based on their location within the anterior, middle, or posterior mediastinum.

💡Hilar Enlargement

Hilar enlargement refers to an increase in the size of the lymph nodes or other structures in the hilum of the lung. The video explains how this can be seen on X-rays and discusses various causes, including malignancy, infection, and other conditions like sarcoidosis.

💡Hilum Overlay Sign

The hilum overlay sign is a technique used in X-ray interpretation to determine whether a mass is located in the hilum or in front of or behind it. The video explains that if pulmonary vessels are visible through the mass, the mass is not in the hilum, which helps in diagnosing the cause of the mass.

Highlights

The video discusses interpreting chest x-rays, focusing on the cardiac silhouette and mediastinum.

Learning objectives include assessing these structures on x-ray and recognizing common abnormalities.

Anatomy of the cardiac silhouette and mediastinum is reviewed, emphasizing their segments.

The difference between PA and AP films is highlighted, particularly how it affects the heart's size appearance.

Cardiomegaly, or an enlarged heart, is the most common abnormal finding, defined using the cardiothoracic ratio.

Left atrial enlargement can be identified by splaying of the coronal angle and the double density sign.

Right ventricular enlargement may present as filling of the retrosternal space on lateral views.

Pericardial effusions can cause a large cardiac silhouette and may present with a water-bottle morphology or the Oreo cookie sign.

Dextrocardia, a congenital anomaly where the heart is on the right side, is mentioned as a rare condition.

A widened mediastinum, generally greater than 8 cm, can indicate various abnormalities.

Mediastinal masses are categorized into anterior, superior, middle, and posterior regions, each with different potential causes.

Hilar enlargement can result from malignancies, infections, or other conditions like sarcoidosis or pulmonary hypertension.

The hilum overlay sign helps differentiate hilar masses from those anterior or posterior to it.

An example of using the hilum overlay sign to identify the location of a mass is provided.

The video concludes with an overview of upcoming topics, including the assessment of the diaphragm and pleura.

Transcripts

this is the fifth video in this series

on how to interpret a chest x-ray and

the topic is the cardiac silhouette and

mediastinum learning objectives are to

be able to assess those structures on

x-ray and to know the common ideologies

of abnormalities seen in them let's take

a look at the anatomy of the cardiac

silhouette and mediastinum that was

first introduced in lesson two for this

lesson it will be important to remember

the structures listed here which

comprise the different segments of that

silhouette this video will be divided in

half the first half will cover

abnormalities of the heart the second

will cover abnormalities of the hila and

the remainder of the mediastinum before

I discuss specific findings I need to

also review another very important

difference between PA and AP films that

I haven't talked about yet let's start

with a PA film and here is an axial

cross-section through the thorax at the

level of the heart the patient's front

is up against a photographic plate at

the top in some of the prior videos I've

sort of implied that the x-ray beams

which are responsible for creating the

x-ray image are all parallel to one

another but this isn't actually true the

x-ray source is a fixed point or close

to a fixed point and therefore the x-ray

beams actually diverge outward as they

get further from their origin for a PA

film this makes not much difference

since the heart is a relatively anterior

structure on the chest it is close to

the film where the x-ray is taken and

therefore the shadow it casts on the

x-ray is an accurate representation of

its true size however how does this

change if the same exact patient has an

AP film taken now there is greater

separation between the heart and the

film as a consequence the diverging

x-ray beams will create a larger shadow

that will exaggerate the size of the

heart

in short the heart size is only accurate

when assessed on APA film some

structures within the mediastinum suffer

from the same effect but to lesser

extent as normal mediastinal structures

tend to be more centrally located within

the thorax to see just how much of a

differences can make here are two x-rays

taken up the same patient minutes apart

notice how much larger the heart appears

on the AP film the upper mediastinum is

also affected but not as much I'll now

talk about some specific abnormalities

of the cardiac silhouette the most

common abnormal finding is cardiomegaly

cardiomegaly simply means that the

overall size of the heart is larger than

normal there are a couple of ways it can

be defined in radiology but by far the

most common way to define it for

analysis of chest x-rays uses the

cardiothoracic ratio this ratio is the

maximum horizontal cardiac width divided

by the maximum horizontal thoracic width

as measured between the inner surfaces

of the ribcage cardiomegaly is said to

be present if this ratio exceeds 50% on

the PA film here are two x-rays looking

at the one on the Left first the red

line represents the maximum horizontal

cardiac width and the purple line

represents the maximum horizontal

thoracic width this is a ratio of 40% or

0.4 which is normal looking at the same

on the right film the heart is obviously

much larger this is a ratio of 60% or

0.6 identifying cardiomegaly on x-ray is

really that simple

as far as the ideologies of cardiomegaly

it can essentially be the consequence of

any cause of left or right side of heart

failure it's important to realize that

pericardial effusions which I'll discuss

in a minute can be indistinguishable

from the cardiomegaly that's a

consequence of an enlarged heart while

the finding of cardiomegaly concerns the

heart as a whole there are two cardiac

chambers

that can be identified as being enlarged

on x-ray individually the first is the

left atrium as discussed in the last

lesson one finding of left atrial

enlargement is splaying of the coronal

angle to a value greater than 90 degrees

the second finding is something called

the double density sign usually the

right border of the left atrium is not

visible on x-ray because it is

contiguous with the right atrium and it

lies right in the middle of the chest

where it usually gets obscured by a

number of other structures however as

the left atrium increases in size it

actually will stretch well across the

midline and create a second shadow along

the right heart border this dark red

line here is the right atrium the pink

line here is the left atrium ideologies

of left atrial enlargement include any

cause of left-sided heart failure also

included is mitral valve disease such as

mitral stenosis mitral regurgitation or

mitral valve prolapse for this

particular x-ray there is a clue as to

why this patient has a large left atrium

while the overall size of the heart is

enlarged suggesting the presence of

heart failure assuming this is a PA film

there's another important finding it is

this round structure right here what is

that

it's the ring of a mitral valve

replacement so this patient has had some

form of mitral valve disease that at

least contributed to the enlarged left

atria the second cardiac chamber whose

enlargement can sometimes be

individually spotted on x-ray is the

right ventricle the main finding of this

is filling of the retrosternal space as

seen on the lateral view consider these

two lateral films have included a normal

one for comparison and examine the

retrosternal space that is the one or

two centimeters directly behind the

sternum in the mid chest region in the

normal film this will be relatively

Lucent however as the right ventricle is

the most anterior of the cardiac

chambers as it enlarges it begins to

occupy the space ideologies of right

ventricular enlargement include any

cause of pulmonary

attention and pulmonary valve disease

the second of which is much less common

in the adult population moving on to

pericardial effusions not all clinically

relevant diffusions are visible on x-ray

particularly if they developed acutely

that's because pericardial tamponade

a condition where diastolic cardiac

filling is impaired due to high intra

pericardial pressure is dependent on

both the volume of fluid within the

pericardium as well as the speed with

which the fluid accumulated the primary

finding of an effusion is a large

cardiac silhouette other findings

include what is frequently called the

water-bottle morphology of the

silhouette as well as something called

the Oreo cookie sign here are two

examples of the water-bottle shape of a

very large pericardial effusion you may

be wondering how in the world these look

like water bottles but the name was

given when water bottles weren't made

out of aluminum or rigid plastic but

rather soft sided materials like leather

next the Oreo cookie sign is a little

amusing it's seen on the lateral film

I'm going to zoom in on this part right

here to understand what you're looking

at you'll need to know what an Oreo

cookie looks like I'm sure there are

parts of the world that are not familiar

with this fantastic mass-produced

artificially flavored treat so here's a

picture the important aspect is that it

consists of a layer of white Cream

Sandwich between two dark supposedly

chocolate flavored discs if you look

really carefully you can actually see

the same configuration in front of the

heart just above the diaphragm it's not

normal to have three layers discernible

here so what's responsible for each the

posterior chocolate layer which is

relatively radiolucent is the

pericardial fat the middle cream layer

which is relatively radio dense is a

pericardial effusion and the anterior

chocolate layer is the epicardial fat

this sign exists because fluid absorbs

ever so slightly more x-rays than fat

does there are many ideologies of

pericardial effusions which can be

divided into those who

cause acute effusions and those which

cause sub acute to chronic effusions

acute effusions can be from trauma viral

pericarditis a complication from

myocardial infarctions such as a

catastrophic free wall rupture or a post

mi inflammatory process called Dressler

syndrome where it can be iatrogenic from

a right ventricular biopsy or from any

one of a number of EP procedures sub

acute and chronic infusions are seen in

malignancies such as lymphoma breast and

lung but can also be due to renal

failure collagen vascular disease like

lupus and rheumatoid arthritis

hypothyroidism and finally tuberculosis

which is the major cause of pericardial

effusions in some parts of the world

before moving on to the mediastinum in

hila i want to briefly mention a

congenital anomaly which although it's

relatively rare tends to be mentioned

during rounds or on tests out of

proportion to its prevalence at first

you might assume this x-ray was loaded

into the system backwards if it wasn't

for the capital R in the upper corner

indicating that in fact the x-ray is in

the correct orientation

this person has dextrocardia which

occurs when the heart loops around in

the opposite direction as normal during

early embryo logic development its

incidence is about 1 in 12,000

pregnancies it may be isolated and

discovered incidentally or it can be

associated with life-threatening

additional congenital malformations now

I'll move on to abnormalities of the

mediastinum and hila the most important

of these abnormalities is a widened

mediastinum this is generally defined as

greater than 8 centimeters on either a

PA or an AP film however most cases of

an apparently widened mediastinum are

due to rotation of the patient poor

inspiratory effort or an AP view to best

understand mediastinal masses which are

responsible for truly widened

mediastinum

one must be familiar with the four

regions of the mediastinum these regions

are not precisely defined by any actual

tissue planes

and their definition varies slightly

between sources but this is

approximately where the divisions live

the first two regions are the anterior

mediastinum which is everything anterior

to the pericardium and inferior to the

sternal angle and superior mediastinum

which is everything superior to the

sternal angle the differential diagnosis

of masses in these two regions overlap

greatly so I'll consider them together

they include lymphoma enlarged thyroid

such as the goiter thymus tumors tumors

called teratomas and when occurring in

just the superior mediastinum an aortic

aneurysm the middle mediastinum includes

everything within the pericardium and is

variably defined to also include the sub

kernel para tracheal and hilar lymph

nodes and the esophagus the differential

diagnosis of masses here include lymph

adenopathy from any cause and a arctic

aneurysm pericardial cysts dilated

esophagus or a hiatal hernia finally the

posterior mediastinum includes

everything behind those structures which

ends up being largely just a

paravertebral space thus the

differential diagnosis of mass is

located here include neurogenic tumors

and extension of spinal masses such as

tumors and infections

I'll show you one or two examples from

each region beginning in the superior

mediastinum we see that there is a mass

here that is actually causing rightward

shift of the trachea although you could

not know it just from this x-ray this

particular patient has a multinodular

goiter this patient has an even larger

mass in the superior mediastinum this

one is from lymphoma anterior

mediastinum masses can easily be missed

especially on p.a films since their

shadow can get lost in the cardiac

silhouette this is a pretty unusual case

in which an anterior mass was not only

visible it was so large it resembled the

water-bottle morphology of a large

pericardial effusion the hint to the

correct diagnosis is from the lateral

film what do you notice here there's an

obliteration of the retrosternal space

while this could be from concurrent

right ventricular hypertrophy as we saw

a few minutes ago in this case it's from

a massive thigh mo lipoma that is

literally wrapped around the anterior

surface of the heart here we see an

unusual bump coming off the left upper

heart border even if I didn't tell you

that this was a middle mediastinal mass

you could still tell that from the lack

of a clear boundary between a normal

cardiac silhouette and the mass here's

the corresponding lateral film to

confirm its placement in the middle

mediastinum its appearance is consistent

with a pericardial cyst which could be

confirmed with a chest CT or

echocardiogram finally here is a

posterior mass you can tell it's not

middle from the PA film because there is

still a very well-defined left heart

border the lateral film confirms this

mass is arising from the posterior

mediastinum in this case biopsy

demonstrated a schwannoma here's an

interesting collection of mediastinal

masses which are critical to accurately

identify these are all a or t'k

aneurysms the one in the middle is

particularly easy to identify given the

calcified walls since only vascular

structures or cysts tend to do that I'll

move on from the mediastinum to talk

about the hila here are two examples of

bilateral hilar enlargement in this case

both patients had stage 1 sarcoidosis

the differential diagnosis of hilar

enlargement is very long and can be

divided into three categories first

malignancy which includes primary lung

cancer lymphoma and metastatic disease

the second category is infection

particularly tuberculosis and viruses

but a whole host of rarer diseases are

included here as well depending on where

in the world you are practicing and

watching this video there may be many

more diseases on your list than listed

here finally in the other category are

sarcoidosis silicosis pulmonary

hypertension a pulmonary artery aneurysm

and a bronchogenic cyst here's another

example of hilar enlargement in this

case the patient had severe pulmonary

hypertension in this case there is

unilateral right-sided enlargement

unfortunately it's associated with this

opacity in the right upper lung that

looks suspicious for a primary tumor

overall the most likely diagnosis here

is a primary lung cancer with a hilar

node metastasis I'll end this lesson by

talking about how one can use the hilum

overlay sign to distinguish a hilar mass

from one anterior or posterior to it

consider this film which has an obvious

mass of some kind in the vicinity of the

left hilum when a mass arises from the

hilum the adjacent pulmonary vessels

will become obscured

if the pulmonary vessels are still

visible through the mass the mass is not

in the hilum if we zoom in on the mass

like this you can still see the outline

of a left pulmonary artery and if we

check the lateral film we see that

indeed the mass is posterior to the

hilum to diagnose the cause of the mass

look here there is a very thin rim of

peripheral calcification that means

either a vascular structure or assist in

this case it was a saccular a or t'k

aneurysm that concludes this video on

the cardiac silhouette and mediastinum

the next video will cover assessment of

the diaphragm and pleura

you