Lecture 1- mediastinum and thorax

Question 1

what is the trachea?

Answer 1

Tubular passageway connecting the upper respiratory tract to the lungs via tracheobronchial tree enabling gas exchange.

Question 2

what are the anatomical landmarks of the trachea

Answer 2

Inferior margin of the cricoid cartilage (C6)
Braches into the left and right main bronchi at the carina (T4) - the plane of Ludwig.
Is in a midline position but can be slightly displaced to the right by the arch of the aorta.
10-1cm with a width of 1.5 - 2 cm (wider in men).

Question 3

what is the plane of ludwig?

Answer 3

separates mediastinum

Question 4

what does the trachea consist of?

Answer 4

Consists of
The fibro-elastic tissue is flexible and expands and contains “C” shaped cartilage rings which gives it rigidity. These are bridged by annular ligaments.
Histology
Outer layer – connective tissue
Middle layer – tracheal cartilage, annular ligaments, connective tissue, trachealis muscle
Inner layer – respiratory mucous membrane

Question 5

what are two examples of tracheal variants?

Answer 5

-lunate trachea
-Diverticulum

Question 6

what’s a lunate trachea?

Answer 6

tracheal variant.

Lunate is flattened, it is associated with conditions like CPD, COPD and respiratory issues.

Question 7

whats a diverticulum?

Answer 7

tracheal variant

Outpouching of tissue between the layers of cartilage

Incidental finding

Don’t cause problems to the patient but it looks like something is wrong.
Can often be mistaken for air in the patients mediastinum.

You would know if it is air if you can’t trace the diverticulum back to the trachea.

Question 8

What is the carina?

Answer 8

• The carina is a ridge of cartilage at the base of the trachea.
• It separates the openings of the right and left main bronchi.
• Level of T4/T5 but moves with breathing
• Lies to left of midline

Question 9

Why is the carina important?

Answer 9

-Important marker for tube position e.g.

-ET tubes should be 5cm above the carina.
-NG tubes should bisect the carina.
-SVC to the right side of the carina for CVC

Question 10

If the carina is widened (more than 100 degrees) this can be a sign of?

Answer 10

• Left atrial enlargement
• Cardiomegaly
• Pericardial effusion
• A mass around the area
• Tumours in the hilum.

Question 11

Bronchi

Answer 11

A respiratory epithelium (shorter than trachea) - lamina propria (denser than trachea) separated by a discontinuous layer of smooth muscle from the submucosa (cartilage are flat plates).

Question 12

Bronchioles

Answer 12

No cartilage, airways must be kept open by radial traction (elastic fibres of the surrounding alveoli pull on the walls of small airways and hold them open). Prominent smooth muscle layer. Adjusting the tone of the muscle layer alters airway diameter so air flow can be controlled.

Question 13

Respiratory bronchioles

Answer 13

No goblet cells, alveoli for gaseous exchange. Have alveolar ducts (rings of smooth muscle, collagen and elastic fibres) – leading to alveolar sacs- leading to alveoli (the terminal sacs of the respiratory sac). Provide majority of the lung volume and surface area. Can communicate between adjacent alveoli through pores of Kohn. Lined with pneumocytes (provide structure and surfactant).

Question 14

what are the lobes of the lung?

Answer 14

• right lung has 3 lobes: superior, middle, inferior.
  -left lung- superior and inferior.

Question 15

The lobes of the lung

Answer 15

• The surface of the visceral pleura that covers the lung is continuous with the visceral pleura that covers the fissures.
• Lung fissures are a double fold of visceral pleura that completely of incompletely invaginates ( be turned inside out or folded back on itself to form a cavity or pouch) the lung parenchyma to form the lung lobes.
• You will often see the horizontal fissure on a PA or AP CXR, and sometimes the oblique fissure on a lateral CXR.

Question 16

Lung fissures- left lung

Answer 16

• Left lung:
  -Oblique fissures separating the upper lobe from the lower lobe.
  -T4/T5 posterior to the hemidiaphragm anteriorly.

Question 17

Lung fissures- right lung

Answer 17

-Oblique fissure separating the upper lobe from the lower lobe
-Horizontal fissure separates the upper lobe from the middle lobe.
-4th costal cartilage from the hilum to the anterior and lateral surfaces of the right lung.
* Mass or fluid can push the fissure up. Movement of fissures is a sign you need to look closely & you can rarely see an oblique fissure on an x ray

Question 18

why are the fissures important for us

Answer 18

• For CT lung biopsy
• They help prevent infections affecting nearby lobes- good way to differentiate between infection and possible malignancy.

Question 19

lobes of the lung- normal variants.

Answer 19

Azygos fissure- the most common accessory fissure seen on a CXR. Looks like a tadpole. Extra fissure.
Doctors may think it is a pneumothorax.

Question 20

ways of viewing the chest on CT.

Answer 20

• All different window levels.
  -Lung- bronchi and bronchioles
  -Bone- ribs, cortex, sternum allows us to see there’s no fractures
  -Soft tissue- see chest wall soft tissue, and the heart.
  -Change windows depending on what you want to see.

Question 21

The pleura

Answer 21

• Covers the lung, chest wall and mediastinum with 2 continuous layers of epithelium.
• Visceral- covers the lungs inner layers. Visceral has no pain sensors. Thin layer of liquid is there to allow movement when we breathe. Too much fluid leads to pleural effusion.
• Parietal- covers the chest wall and is the outer layer. Nerve supply is the phrenic nerve so inflamed pleura can cause ipsilateral shoulder tip pain.
• Separated by a thin layer of liquid.
• You can only see the pleura and pleural spaces on the plain film when they are abnormal.
• Lung markings should reach the thoracic wall on a CXR.
• There should be no space between the pleura.

Question 22

what is the mediastinum

Answer 22

• It is the space in the midline of the chest between the pleura of each lung and extends from the sternum to the vertebral column.

Question 23

What does the mediastinum contain

Answer 23

• Contains all the thoracic viscera except the lungs wich are:
  -Heart, great vessels, oesophagus, trachea, phrenic nerve, cardiac nerve, thoracic duct, thymus, mediastinal lymph nodes.

Question 24

what can the mediastinum be divided into

Answer 24

• Can be divided into parts based on their relationship to the pericardium.
• Superior mediastinum- above the level of the pericardium and plane of Ludwig,
• Inferior mediastinum- below the plane of Ludwig
• Anterior mediastinum- anterior to the pericardium
• Middle mediastinum- within the pericardium
• Posterior mediastinum- posterior to the pericardium.

Question 24

why does diving the mediastinum matter?

Answer 24

Different pathologies can be seen in different areas, which is why it is separated.
-Posterior- thoracic spine, lymphoma, neurogenic mass.
-Middle mediastinum- aneurysm, bronchogenic cyst, diaphragmatic hernia.
-anterior mediastinum- germ-cell tumour, lymphoma. substernal thyroid.

Question 25

normal variants in mediastinum?

Answer 25

-epicardial (pericardial) fatpads.
-discrepency in aorta

Question 26

epicardial fatpads

Answer 26

*Epicardial (pericardial) fat pads are normal structures that lie in the cardiophrenic region, more so on the right. More prominent in obese patients.
*Can be affected by fat necrosis
*On plain film may see a mass or hazy opacity in the costodiaphragmatic angle. The cardiac and diaphragmatic silhouettes are usually visible.
*Differential diagnosis includes
–Lipoma or pericardial tumour
–Pericardial cyst
–Morgagni hernia
–Pericardial lymphadenopathy
–Pleural tumour

Question 27

Discrepancy in aorta

Answer 27

• Discrepancy in aorta, gets longer and twists and unfolds.
• Completely normal but there just isn’t a tight aortic arch.
• Refers to the widened appearances of the aortic arch on a PA or AP CXR. It is one of the more common causes of mediastinal widening and is seen with increasing age.
• *Occurs due to discrepancy in the growth of the ascending aorta with age, where the length of the ascending aorta increases out of proportion with diameter causing the plane of the arch to swivel.

Question 28

What is the hilum.

Answer 28

• May be at the same level but commonly the left is higher than the right
• Should look similar in appearance
• Anatomical landmark- anteriorly 3-4th costal cartilage, posteriorly T5-T7
• Hila-one / hilum- both
• Consists of o: pulmonary artery, two pulmonary veins, main bronchus. Bronchial vessels, nerves and lymphatics.
• Hila should look like each other- looking for symmetry
• Generally, about the same height, but the left side can be slightly higher because of the heart.

Question 29

What does the skeleton of the thorax include>

Answer 29

The skeleton of the thorax includes the sternum, ribs and costal cartilages and thoracic vertebra and intervertebral discs.

Question 30

what is the costal cartilage?

Answer 30

The costal cartilage are bars of hyaline cartilage that serve to prolong the ribs forward and contribute to the elasticity of the walls of the thorax.
* *Is only found at the anterior ends of the ribs, providing medial extension.
* *The first 7 pairs are connected with the sternum. The next 3 are each articulated with the lower border of the cartilage of the preceding rib. The last 2 have pointed extremities which end in the wall of the abdomen.
* *They increase in length from 1-7 and then gradually decrease to the 12th. They are broad at their attachments to the ribs, and taper toward their sternal extremities.

Question 31

The sternum

Answer 31

t is there to protect the heart and mediastinum
* Sternum fracture is often caused by a traumatic injury, so doctors are more likely to use CT, lateral view.
* R is abnormal as its difficult to trace the lines, it is a fractured sternum that has not healed well..
* An old fracture that has tried to heal as there is callous formation.

Question 32

The ribs

Answer 32

• On a chest XR ribs increase in length from 1-7.
• Don’t XR for fractured ribs unless there is a risk of a pneumothorax due to significant trauma.

Question 33

Ribs- normal variants.

Answer 33

• costal cartilage calcification
  -Cervical Rib
  -Bifid ribs

Question 34

Costal cartilage calcification.

Answer 34

Costal cartilage calcification
* With age, costal cartilage becomes calcified.
* Completely benign and incidental.
* Different densities in the image due to the calcification but makes it harder to see things in the lungs.

Question 35

Cervical rib

Answer 35

Accessory rib that comes off C7.
Generally bilateral, can occasionally get more than one.
More common in women.
Can cause problems such as thoracic output syndrome.

Question 36

Bifid ribs

Answer 36

• Ribs can split into two separate ribs.

Question 37

what is the diaphragm.

Answer 37

*The diaphragm is a C shaped structure of muscle and fibrous tissue that separates the thoracic cavity from the abdomen. It has peripheral attachments to structures that make up the abdominal and chest walls. The muscle fibres converge in a central tendon, which forms the crest of the dome. Its peripheral part consists of muscular fibres that take origin from the circumference of the inferior thoracic aperture and converge to be inserted into a central tendon.

Question 38

what is the function of the diaphragm?

Answer 38

–Main muscle of respiration. During inhalation the diaphragm contracts and moves inferiorly enlarging the volume of the thoracic cavity and reducing intra-thoracic pressure (external intercostals also participate), forcing the lungs to expand. The diaphragm is also involved in non-respiratory functions helping to expel vomit, faeces and urine form the body by increasing intra-abdominal pressure, aiding in childbirth.
–If either the phrenic nerve, cervical spine or brainstem is damaged this will sever the nervous supply to the diaphragm. The most common damage to the phrenic nerve is by bronchial cancer, which usually only affects one side of the diaphragm.

Question 39

what happens above and below the diaphragm?

Answer 39

*From above the diaphragm receives blood from branches of the internal thoracic arteries, from the superior phrenic arteries which arise from the thoracic aorta, and from the lower internal intercostal arteries. From below the inferior phrenic arteries supply the diaphragm.
*The diaphragm drains blood into the brachiocephalic veins, azygos veins and veins that drain into the inferior vena cava and left suprarenal vein