These are axial views of the chest with emphasis on the mediastinum as seen by Computed Tomography. The numbered lines on the scout view to the far left correspond to the numbered thumbnail images at the bottom. Click on one of these thumbnail images to show a larger numbered version of the image to the near left.
Click on a number or anatomic structure on the image to the left and the text in this frame will advance to the text corresponding to the structure.
1. Trachea
The trachea connects the upper respiratory
tract to the lower respiratory tract. It is about 9-15 cm in length.
It is located in front of the esophagous and behind the thyroid
gland in the neck. It is considered to be in the superior and
middle mediastinum. It is made up of 16-20 incomplete hyaline
cartilaginous rings that are open posteriorly. The trachea bifurcates
into the right and left main stem bronchus at a location called
the carina, which is located at the level of the sternal angle
(T4-T5). Tracheomalacia is a disorder in infants where the
trachea lacks structural support so that the negative airway pressures
generated during inspiration causes the trachea to collapse.
This results in a stridorous inspiratory noise.
2. Esophagus
The esophagus connects the upper digestive
tract to the lower digestive tract. It is 25-30 cm in length.
The esophagus is considered to be located in the superior and
posterior mediastinum. It has relations to the trachea which is
anterior to the esophagus. The thoracic duct sits to the left
of the esophagus in the superior mediastinum. The esophagus enters
the thorax by penetrating the diaphragm at the esophageal hiatus
at the level of T10 The upper half is formed by striated
muscles fibers where as the lower half is formed by smooth muscle.
Cancers in the upper esophagus are usually squamous whereas cancers
of the lower esophagus are adenocarcinomas.
The blood supply to the esophagus comes from
the aorta as well as from the left gastric and inferior phrenic
arteries. The esophageal veins empty into the portal venous system.
Esophageal varices are dilated veins of the esophagous seen in
conditions of portal hypertension, a condition in which there
is obstruction to the blood emptying into the portal system. The
most common cause of portal hypertension is cirrhosis of liver
in chronic alcoholics. The esophagus is different than other organs
of the digestive tract in that it lacks a serosa. This makes the
esophagus susceptible to perforation during endoscopy when a scope
is placed into the esophagus to visualize it.
3. Trapezius muscle
The trapezius is a large back muscle shaped
into the shape of trapezoid. It is one of the superficial muscles
of the back. It has origins in the spinous processes of C7-T12
vertebrae and inserts to the lateral aspect of the clavicle and
scapula. The trapezius attaches the pectoral girdle to the skull
and vertebral column. Its actions include elevating, depressing,
rotating and retracting the scapula. The trapezius derives its
enervation from the spinal accessory nerve (CNXI).
4. Left Clavicle
The clavicle is a bone that extends horizontally
at the base of the neck from the manubrium of the sternum to the
acromium of the scapula. Its medial end articulates with the sternum
at the sternoclavicular joint. The other end articulates with
the scapula through the acromioclavicular joint. It serves to
attach the upper limb to the axial skeleton. It also provides
attachment for muscles such as the pectoralis major and deltoid
muscle. Fractures of the clavicle occur and is found to be concomitant
with fractures of the scaphoid in the hand. The mechanism is usually
due to falling on an outstretched hand.
4*. Right Clavicle
As described above for the Left Clavicle.
5. Subscapularis
Muscle
This is one of the muscles of the rotator cuff,
which is a group of four muscles also including the supraspinatus,
infraspinatus, and teres minor. These four muscles are responsible
for providing stability for the shoulder joint by holding the
head of the humerus in the glenoid cavity of the scapula. The
subscapularis sits anterior to the scapula and posterior to the
serratus anterior muscle. The origin of this muscle is located
at the subscapular fossa of the scapula. The muscle inserts in
the lesser tubercle of the humerus. The action of the muscle is
to medially rotation and adduction of the arm. The muscles is
enervated by the lower subscapular nerve (C5-C7).
6. Infraspinatus
Muscle
This muscle is also one of the members of the
rotator cuff group. It originates from the dorsal aspect of the
scapula and inserts into the greater tubercle of the humerus.
It also sits inferior to the spine of the scapula. It action is
to laterally rotate the arm and also help stabilize the shoulder
joint. It is enervated by the subscapular nerve.
7. Supraspinatus
Muscle
This muscle is another member of the rotator
cuff. It originates in the supraspinatus fossa of the scapula,
which is located above the spine of the scapula. The muscle inserts
into the superior aspect of the greater tubercle of the humerus.
It is innervated by the subscapular nerve. The actions of the
muscle include helping the deltoid muscles to abduct the arm.
As with other rotator cuff muscles, it helps stabilize the shoulder
joint.
8. Pectoralis Major
Muscle
The pectoralis muscle is a large muscle that
sits in the anterior thorax. It is enclosed by a fascial sheath
which laterally forms the axillary fascia. The pectoralis major
is superficial to both the pectoralis minor and serratus anterior
muscles. It has multiple origins including the medial half of
the clavicle and also the anterior surface of the sternum in the
first six costal cartilage. It inserts into the greater tubercle
of the humerus. Its actions include adducting and medially rotating
the humerus. It is innervated by the medial and lateral pectoral
nerves.
9. Pectoralis
Minor Muscle
This muscle is located deep to the pectoralis
major muscle. It originates from the costal cartilage of ribs
3-5 and inserts on the coracoid process of the scapula. It is
enervated by the medial pectoral nerve. This muscle serves
to pull the scapula inferiorly and anteriorly to stabilize it.
10. Serratus
Anterior Muscle
This muscle is located in the lateral aspect
of the thorax. It originates from the external surface of the
lateral parts of ribs 1-8. It inserts on the anterior surface
of the medial border of the scapula. The muscle sits anterior
to the subscapularis muscle. It is enervated by the long thoracic
nerve (C5-C7). Known as the boxer's muscle, it is important because
it functions to pull the scapula toward the thorax in the forward
swing of the arm. Injury to the long thoracic nerve deprives this
muscle of its enervation and results in a "winged-scapula". In
this condition, the scapula protrudes out in the back when the
arm is abducted. There is also a limitation in that the arm cannot
be abducted above the horizontal plane.
11. Latissimus
Dorsi Muscle
This muscle is one of the largest muscles of
the body and is appropriately named so in Latin as the widest
of the back. This massive muscle covers extends from the lower
back and inserts into the crest of the lesser tubercle and intertubercular
groove of the humerus. It originates from the spinous processes
of the inferior six thoracic vertebrae and last four ribs. It
is enervated by the thoracodorsal nerve (C6-C8). Its actions include
extending, abducting, and medially rotating the humerus. It
is the muscle used in raising the body in climbing activities.
It is located deep to the trapezius muscle. It is also located
also inferior to the teres major and teres minor muscles.
12. Erector Spinae
Muscles
This is a group of 3 muscles sitting parallel
to the vertebral column laterally on both side of the spinous
process of each vertebral process. The three groups of muscles
making up the erector spinae are the iliocostalis, longissimus,
and spinalis muscles. These muscles extend from the cervical
vertebrae down to the tubercles of the 9th to 10th ribs. The
function of the muscles are to extend the vertebral column.
13. Left Subclavian
Artery
This artery is the third branch of the ascending
aorta. The first branch is the brachiocephalic trunk. The
second branch of the aorta is the left common carotid artery. The
vessel rises to enter the root of the neck to enter the upper
limb. The vessel is related to the anterior scalene muscle anteriorly.
This muscle divides the subclavian artery into three parts which
are medial, lateral, and deep to the muscle. The subclavian
artery forms important branches which include the internal thoracic
artery, vertebral artery, thyrocervical artery, costocervical
trunk, and dorsal scapular artery.
13* Distal
Subclavian Artery
The distal portion of the subclavian artery
eventually forms the axillary artery after it crosses over the
first rib. The axillary artery then becomes the brachial
artery after it crosses the inferior border of the teres major
muscles.
14. Left Common Carotid
Artery
The left common carotid originates directly
from the arch of the aorta and ascends in the neck while it is
encased in the carotid sheath. It then divides into the external
carotid and internal carotid at the superior border of the thyroid
cartilage. The carotid sheath also encases the vagus nerve
and the internal jugular veins. The vagus nerve is found
in a posterior position in the carotid sheath while the internal
jugular veins are found lateral to the common carotid artery.
14* Right Common Carotid
Artery
This vessel arises from the brachiocephalic
trunk. It is one of the two branches of the brachiocephalic
trunk, the other being the right subclavian artery. The carotid
body is found at the bifurcation of the internal and external
carotid vessels and it serves to measure the pO2 and pCO2 in the
arterial blood.
15. Left Internal
Jugular Vein
The internal jugular vein drains the blood
supply of the face and the brain. It is the biggest vein in the
neck. The vein starts at the jugular foramen as a continuation
of the sigmoid sinus. As it travels in the neck, it is encased
in the carotid sheath. It is found lateral to the common carotid
artery and anterior to the vagus nerve . The vessel joins
with the subclavian vein to form the brachiocephalic vein which
then enters the superior vena cava. It is possible to cannulate
(insert a intravenous line for volume resuscitation) into the
internal jugular vein since it is located in a superficial position. At
the base of the neck, the vessel can be found medial to the sternocleidomastoid
muscle and deep to the medial end of the clavicle.
15* Right Internal
Jugular Vein
See above for left internal jugular vein. Usually
larger than the left IJV because of the larger volume of blood
entering it from the sigmoid sinus.
16. Scapula
The scapula and the clavicle are two bones
that make up the pectoral girdle. Together these two bones serve
to connect the upper limb to the axial skeleton. The scapula
sits in the posterior aspect of the thorax. It has a spine on
its posterior surface which forms the acromion. The supraspinatus
fossa is located above the spine and the infraspinatus fossa is
located below the fossa. The acromion wraps around the scapula
superiorly and articles with the lateral end of the clavicle at
the acromial-clavicular joint. The glenoid fossa is a pocket in
the superior and lateral part of the scapula that serves as a
surface for articulation for the head of humerus. The coracoid
process of scapula is the insertion point for the pectoralis minor
muscle.
17. First Rib
The first rib is the widest and most curved
of the ribs. It is important because it provides an attachment
point called the scalene tubercle for the anterior scalene muscle. The
subclavian artery, vein, and brachial plexus travels over the
first rib to enter the upper limb. The subclavian vein travels
anterior to the anterior scalene muscle while the other two structures
travel posterior to this muscle. Moreover, these structures
are found posterior to the clavicle. It is has to palpate
the first rib because it sits behind the
clavicle.
17*. Second Rib
This rib is longer and less curved than the
first rib.
18. Manubrium of
Sternum
The manubrium of sternum is the broadly-shaped
superior part of the sternum that articulates with both the clavicle
and the first rib. The superior aspect of the manubrium has a
notch on it that is easily palpable.
18*. Body of Sternum
This part of the sternum is inferior to the
manubrium. It articulates with ribs 2-7. It is longer
and more narrow than the manubrium. It forms the anterior and
medial part of the thorax.
18+.
Xiphoid Process of Sternum
This is the most inferior part of the sternum. It
is the short and pointed end of the sternum. It is cartilaginous
up until middle age when it starts to ossify and join with the
body of the sternum.
19. Aortic Arch
The arch of the aorta is found at about the
level of the sternal angle. It is a continuation of the ascending
aorta which is found in the middle mediastinum. The aorta
arches over the root of the left lung and travels posteriorly
and to the left to travel to the left of the trachea and esophagous. The
aorta then becomes the descending aorta and it travels in the
posterior mediastinum. On chest X-rays, the arch of the aorta
casts a shadow that is seen and called the aortic knob. An
important anatomic relationship here is that the left recurrent
laryngeal nerve winds around the arch of the aorta posterior to
the ligamentum arteriosum and then travels in between the trachea
and esophagous. The ligamentum arteriosum is the embryonic remnant
of a vessel that allowed blood to shunt from the pulmonary artery
into the aorta. This is because of the high resistance to blood
flow in the pulmonary circulation of a fetus.
19*. Ascending
Aorta
The first part of the aorta. The ascending
aorta is found in the anterior mediastinum and arches back towards
the posterior mediastinum. The ascending aorta is found to
the left of the superior vena cava and to the right of the pulmonary
trunk. Its first branch is the right brachiocephalic trunk.
It arches over the right pulmonary artery. The thymus gland
gland is found covering the ascending aorta.
19+. Descending
Aorta
Descending aorta is a continuation of the arch
of the aorta. In the thorax, the descending aorta is found
to the left of the vertebral column and posterior to the esophagous.
It is also to the left of the thoracic duct and anterior to the
hemiazygous vein. It pierces the diaphragm at T12 to enter
the abdomen. The thoracic duct and azygous vein also accompany
the aorta through this hiatus. In the thorax, the aorta gives
off nine paired intercostal arteries, esophageal, pericardial,
superior phrenic, and bronchial arteries.
20. Azygous Vein
The name in Latin means unpaired and it well
describes the course of this vein. It drains the blood from the
abdomen and posterior thorax. It originates at a point posterior
to the IVC and the renal vein. It enters into the thorax
through the aortic hiatus at T12 and ascends in the thorax posterior
to the aorta. It is also posterior to the thoracic duct. The
azygous is located to the right of the vertebral column while
the hemiazygous system of veins is located to the left.
20*. Arch
of the Azygous
The azygous vein arches over the root of the right
lung and then empties into the superior vena cava.
21. Right Brachiocephalic Vein This vein is formed by the right internal jugular vein and the right subclavian vein. The junction is located behind the medial end of the right clavicle. It is a short vein and is only half the length of the left brachiocephalic vein.
21*. Left Brachiocephalic
Vein
The left brachiocephalic vein is a vein that
is formed by the union of the left internal jugular and left subclavian
vein. This vein travels to the right and unites with the right
brachiocephalic vein behind the manubrium of the sternum. The
thymus is located anterior to this vein. The thoracic duct, a
vessel that drains lymph from the lower extremities and pelvis,
also empties into the left brachiocephalic vein.
22. Superior Vena
Cava
The superior vena cava is an organ that is
formed by the junction of the right and left brachiocephalic veins. It
is a tributary that drains blood from the head, upper extremity,
23. Thymus
Gland
The thymus is a gland that is located in the
anterior part of the superior mediastinum. In children, the thymus
is large and is readily recognizable on a chest x-ray. The
thymus involutes in adults starting at pubery. In this patient,
it is seen on the CT. The organ serves as a role in the development
of T lymphocytes in the immune system. The thymus is a site
of carcinoma called malignant thymoma. In a disease called
myasthenia gravis, 15% of patients have a malignant thymoma.
24. Teres
Major Muscle
This muscle sits inferior to the teres minor
muscle. It originates from the inferior angle of the scapula
and inserts in the intertubercular groove of the humerus. It is
enervated by the lower subscapular nerve. Its function is
to adduct and medially rotate the arm. The muscle also extends
the arm from a flexed position. Although not considered as
one of the rotator cuff muscles, the teres major does help in
stabilizing the shoulder joint by holding the head of the humerus
in the glenoid cavity.
25. Teres Minor
Muscle
This muscle is a fourth member of the rotator
group. It originates from the superior part of the lateral border
of the scapula and inserts in the greater tubercle of the humerus.
Like the teres major, the teres minor is located also below the
spine of the scapula. It serves to adduct and medially rotate
the arm. It is enervated by the axillary nerve. It sits superior
to the teres major muscle.
26. Left Subclavian
Vein/Axillary Vein
This originates from the brachial vein which
drains the blood supply from the upper limb. It travels anterior
to the anterior scalene muscle but posterior to the clavicle. It
also goes over the first rib to join with the internal jugular
vein to form the
brachiocephalic vein.
27. Brachiocephalic
Artery
This vessel is the
largest branch of the aorta. It gives rise to the right subclavian
and right common carotid vessels at a location that is posterior
to the right sternoclavicular joint.
28. Inferior
Vena Cava
The inferior vena cava is one of the three
veins that drain into the right atrium. The other two are the
superior vena cave and the coronary sinus. The IVC is a large
vessel that originates at serves as a tributary for the iliac
veins, mesenteric veins, and pelvic veins, hepatic, left renal
veins. It forms at the level of the pelvis from the union
of the right and left iliac veins. The IVC travels to the
right of the abdominal aorta as it ascends into the abdomen. It
also goes from a posterior to an anterior position with respect
to the aorta. The IVC then pierces the diaphragm at its hiatus
at the level of the eighth thoracic vertebra (T8) to enter the
thorax.
29. Pulmonary Trunk.
This is the outlet of the right ventricle. It
is a structure that is about 5 cm. in length. It carries deoxygenated
blood to the lungs. The pulmonary trunk is the origin of
the right and left pulmonary arteries.
30. Right Pulmonary
Artery
This vessel supplies the lungs with deoxygenated
blood that has returned from the body. This vessel has relationships
with both the ascending aorta and the superior vena cava. The
vessel travels inferior to the arch of the aorta. It is found
posterior to the superior vena cava. It is also found posterior
to the right pulmonary vein in the right hilum.
30*. Left Pulmonary Artery
The left pulmonary artery is found anterior
to the descending aorta. It is also connected to the arch of the
aorta by a connection called the ligamentum arteriosum. This
latter structure allows for a way for blood to bypass the high
resistance circulation of the lungs and go towards the body. In
the fetus and newborn, this connection is patent. The left recurrent
laryngeal nerve also loops around the arch of the aorta at this
junction to return to the neck.
31. Thoracic
Duct
The thoracic duct is a vessel that drains lymph
from the lower extremities, pelvis, abdomen, and left side of
thorax. It originates from the cysterna chyli and travels
anterior to the vertebral column and swings to the left as it
reaches the thorax. It eventually drains into the left brachiocephalic
vein.
32. Carina of Trachea
This is where the trachea bifurcates into the
right and left main stem bronchi. The location of this bifurcation
is found at about the level of the arch of the aorta or T5. The
right main stem bronchus takes a more vertical course at the carina.
On x-ray the carina is often visualized. Any distortion of the
normal appearance of the carina indicates pathology such as enlarged
lymph nodes at the level of the carina.
33. Right Ventricle
This chamber of the heart receives deoxygenated
blood from the right atrium and pumps it towards the lungs where
the blood is then enriched with oxygen. This part of the heart
is most proximal to the anterior of the thorax. It receives
most of its blood supply from the right coronary artery. There
is a tricuspid valve that sits in between the right atrium and
ventricle. The right ventricle has well developed thick muscles
called trabeculae carnae. In a condition called cor pulmonale,
the right ventricle enlarges in responses to increase in the resistance
of blood flow through the lungs. The enlargement of the right
ventricle then causes further deterioration in the cardiac performance
and eventually heart failure.
34. Right Atrium
The right atrium is the first chamber of the
heart that receives deoxygenated blood returning from the body.
It receives blood from the coronary sinus, superior vena cava,
inferior vena cava. It receives its blood supply from the right
coronary artery. Atrial septal defects occur when there is
a communication between the right and left atria. This allows
oxygenated blood from the left atrium to leak over to the right
atrium. This causes enlargement of the right atrium due to
an increases in pressure in the right atrium. The atrial
septal defect is a result of patent foramen ovale in a newborn. This
condition can allow emboli originating from the venous side of
the body to travel to the arterial side. The condition may,
for example, present as a stroke in an adolescent.
35. Left Atrium
The left atrium receives oxygen-rich blood
returning from the lungs through the pulmonary veins. The
left atrium then pumps the blood to the left ventricle which then
delivers the blood to the body. The left atrium is often
a source for formation of thrombi in a condition called mitral
stenosis. This condition results when there is a obstruction
of blood flow from the left atrium to left ventricle. This
then results in enlargement of the left atrium and wall motion
abnormalities in the left atrium. Thrombi may form and cause
strokes when they travel to the brain. On a lateral x-ray film
of the thorax, an enlarged left atrium is seen as a bulge in the
posterior of the heart. The enlarged left atrium can indent
the esophagus.
36. Left Ventricle
The left ventricle is the chamber that is responsible
for generating high pressures in order to deliver the oxygenated
blood to the body. The chamber has a mitral valve that has
two cusps instead of the three cusps on the other three valves
of the heart. The mitral valve prevents blood leaking out of the
chamber into the left atrium. It has strong muscle called chordae
tendonae that hold the aortic valve in place to prevent leakage
of blood out of the left ventricle as it is pumping. The left
ventricle is supplied by the left anterior descending coronary
artery and the left circumflex artery. The left ventricle
can enlarge in people with chronic high blood pressure.
On a lateral x-ray film of the thorax, the enlarging left ventricle
is seen as a posterior part of the heart that has enlarged. This
enlargement is inferior to the left atrium.
37. Right Pulmonary
Vein
This vessel delivers oxygen rich blood from
the lungs to the left atrium. It is found inferior to the
level of the pulmonary arteries. There is usually a superior
and inferior set of pulmonary arteries. The right pulmonary
veins are found anterior to the right pulmonary arteries in the
right hilum.
37*. Left Pulmonary Vein
The left pulmonary veins are usually superior
to the right pulmonary veins.
38. Interventricular
Septum
This is the muscle between the left and right
ventricles.
39. Coronary Sinus
This is the large vessel that drains the blood
supply of the heart and returns it to the right atrium. This vein
travels in a groove between the left atrium and left ventricle.
It is a tributary for the great, middle, and small cardiac veins.
40. Tricuspid valve
One of the four valves within the heart, this
three cusped valve separates the right atrium from the right ventricle.