Lower respiratory system and mediastinum- normal appearances

Question 1

what is the trachea?

Answer 1

The trachea is a tubular passageway connecting the upper respiratory tract to the lungs via the tracheobronchial tree enabling gas exchange.

Question 2

What are the trachea anatomical landmarks?

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 does the trachea consist of?

Answer 3

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 4

Trachealvariants – Lunate trachea

Answer 4

Where the tranchea has a flattened shape like a crescent. Can be associated with tracheomalacia or COPD.

Question 5

What is Tracheomalacia?

Answer 5

Tracheal has a tendency to collapse on expiration, cartilage is weak. Can make intubation difficult.

Question 6

Tracheal variants - diverticulum

Answer 6

Normally incidental. But can mimic pneumomediastinum so that’s why we worry

Question 7

What is the carina?

Answer 7

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 8

Why is the carina important?

Answer 8

Important marker for tube position

ET tubes should be 5cm above the carina

NG tubes should bisect the carina

SVC is to the right side of the carina for CVC (central venous catheter) position.

Marker for CTPA scans

Question 9

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

Answer 9

Left atrial enlargement
Cardiomegaly
Pericardial effusion
A mass around the area

Question 10

Trachea to bronchopulmonary segments

Answer 10

Trachea

Left main bronchus, right main bronchus (Primary)

Lobar bronchi (Secondary)

Segmental bronchi (Tertiary)

Bronchopulmonary segments

Question 11

Bronchi

Answer 11

respiratory epithelium (shorter than trachea) – lamina propria (thin layer of connective tissue) is (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. 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 sac of the respiratory tract. Provide the 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

The lobes of the lung

Answer 14

The visceral pleura is a thin membrane that covers the surface of the lungs. This same membrane also extends into the lung fissures.

Lung fissures are formed by a double layer of visceral pleura that partially or completely separates the lung tissue (parenchyma) into distinct lobes.

You will often see the horizontal fissure on a PA or AP CXR, and sometimes the oblique fissure on a lateral CXR.

Question 15

Lung fissures- left and right lung

Answer 15

Left lung
Oblique fissure separating the upper lobe from the lower lobe
T4/T5 posterior to the hemidiaphragm anteriorly

Right lung
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.

Question 16

Why are the fissures important for us?

Answer 16

For CT lung biopsy
They help protect infections affecting nearby lobes – good way to differentiate between infection and possible malignancy.
Allows proper expansion of the lungs.

Question 17

The lobes of the lung – normal variant: Azygos fissure

Answer 17

The most common accessory fissure seen on a CXR

Question 18

What do the lungs look like on CT?

Answer 18

‘Lung window’
lungs W:1500 L:-600
Axial slice

Question 19

Different ways of viewing the chest on CT

Answer 19

Soft tissue

Bone

Lung

Question 20

What is the pleura?

Answer 20

Covers the lung, chest wall and mediastinum with 2 continuous layers of epithelium

Visceral – covers the lungs inner layer

Parietal – covers the chest wall and is the outer later. Nerve supply is the phrenic nerve so inflamed pleura can cause ipsilateral shoulder tip pain

Separated by a thin layer of liquid.

The layer of fluid there is to allow movement when we breathe.

Too much fluid leads to pleural effusion.

Question 21

When can you see the pleura and pleural spaces on plain film?

Answer 21

You can only see the pleura and pleural spaces on 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

The mediastinum contains all the thoracic viscera except the lungs
Which are:

Answer 23

Heart
Great vessels
Oesophagus
Trachea
Phrenic nerve
Cardiac nerve
Thoracic duct
Thymus
Mediastinal lymph nodes

Question 24

What are the divisions of the mediastinum based on their relationship to the pericardium?

Answer 24

Superior mediastinum – above the level of the pericardium and plane of Ludwig

Inferior mediastinum – below the plane of Ludwig:

Anterior mediastinum – anterior to pericardium

Middle mediastinum – within the pericardium

Posterior mediastinum – posterior to the pericardium

Question 25

What is the superior mediastinum and its contents.

Answer 25

Is an artificially divided wedge shaped compartment of the mediastinum located between the thoracic plane inferiorly and the thoracic inlet superiorly.

*Contents
–Muscles –origin of sternohyoid, sternothyroid, and lower end of longus colli muscles
–Arteries – aortic arch and great vessels
–Veins – right and left brachiocephalic veins, left superior intercostal vein, upper half of superior vena cava
–Nerves – phrenic, vagus and cardiac nerves, cardiac plexus, left recurrent laryngeal nerve
–Lymph nodes – brachiocephalic, tracheobronchial, paratracheal
–Trachea
–Oesophagus
–Thoracic duct
–thymus
oBorders
oSuperiorly – thoracic inlet
oInferiorly – thoracic plane
oLaterally – mediastinal pleura
oAnteriorly – manubrium of the sternum
oPosteriorly – bodies of upper 4 thoracic vertebra

Question 26

What is the inferior mediastinum and its contents

Answer 26

Anterior - *Is the portion of the mediastinum anterior to the pericardium and below the thoracic plane
*Contains the thymus, lymph nodes and may contain portions of a retrosternal; thyroid.
Middle - *Is the largest component of the inferior mediastinum.
*Contains the pericardium, heart, great vessels joining the heart (ascending aorta, pulmonary trunk, lower half of the superior vena cava, tracheal bifurcation and both main bronchi. Phrenic nerves, cardiac plexus
Posterior - *It is continuous with the retropharyngeal space via the posterior part of the superior mediastinum
*Contains – descending aorta, azygos-hemiazygos venous system, oesophagus, thoracic lymph nodes, thoracic duct

Question 27

Normal variants in the mediastinum

Answer 27

*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 28

Normal variants in the mediastinum- appearances and occurrences

Answer 28

*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 29

Hila / Hilum

Answer 29

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

Question 30

What does the hilum of the lung involve?

Answer 30

• pulmonary artery
• 2 pulmonary veins
• main bronchus
• bronchial vessels
• nerves and lymphatics.

Question 31

Silhouette sign

Answer 31

Silhouette Sign Summary

The silhouette sign indicates the loss of a normal outline (silhouette) on a chest X-ray and helps to localize abnormalities (e.g., airspace opacities, atelectasis, or masses).

Key Localizations:
Right paratracheal stripe: Right upper lobe.
Right heart border: Right middle lobe or medial right lower lobe.
Right hemi-diaphragm: Right lower lobe.
Aortic knuckle: Left upper lobe.
Left heart border: Lingular segment of left upper lobe.
Left hemi-diaphragm/descending aorta: Left lower lobe.
Basis for Related Signs:

Hilum Overlay Sign:
If the hilum silhouette is intact but a mass appears dense, the mass is not in contact with the hilum (e.g., can see vessel edges).
Cervicothoracic Sign:
Lesions above the clavicles are posterior in location.
Thoracoabdominal Sign:
If a lesion extends below the diaphragm, it is posterior in the thorax.

Other Causes of Silhouette Loss:
Not always due to lung disease:
Right heart border: Pectus excavatum.
Posterior heart border (lateral view): Hiatus hernia.
Lateral Chest X-Ray:
Posterior heart border + left hemi-diaphragm: Left lower lobe.
Anterior right hemi-diaphragm: Right middle lobe.
Posterior right hemi-diaphragm: Right lower lobe.

Question 32

Chest wall and diaphragm: What does the skeleton of the thorax include?

Answer 32

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

Question 33

What is the sternum and what does it consist of?

Answer 33

Function:
Connects ribs via cartilage.
Protects the heart, lungs, and major blood vessels.

Parts of the Sternum:
Manubrium (T3-T4 level):
Jugular notch: Palpable at T3 level.
Notches on each side for the medial ends of the clavicles.
1st costal cartilage attaches to the sides.
Body (T5-T10 level).
Xiphoid process (lower end).

Sternal Angle:
Junction of manubrium and body.
Palpable transverse ridge (~5 cm below the jugular notch).

Question 34

What is the sternal angle?

Answer 34

The sternal angle is a bony landmark at the T4/T5 vertebral level. It indicates the manubriosternal junction and the level of the second costal cartilages so is useful when counting ribs.

Question 35

The body of the sternum

Answer 35

The body of the sternum is about twice as long as the manubrium and is notched on each side to receive costal cartilages 2 – 10, this provides a stronger attachment and prevents rib separation. transverse ridges can indicate its development from several pieces. The costal cartilages of the 2 -10 ribs connect to the body of the sternum to form the rib cage.

Question 36

What is the union of the body of the sternum with the xiphoid process called?

Answer 36

The xiphosternal joint (the union of the body of the sternum with the xiphoid process) is usually firbrocartilaginous but can ossify. It is usually at the level of T10-T11.

Question 37

What is the xiphoid process?

Answer 37

The xiphoid process is a small piece of hyaline cartilage that contains a bony core. Lies in the epigastric fossa. It slowly ossifies throughout childhood and adulthood until around age 40 all the cartilage is replaced with bone.
*The xiphoid process serves as an important attachment point for the tendons of the diaphragm, rectus abdominus and transverse abdominus muscles.

Question 38

What are ribs and how many are there?

Answer 38

*There a 24 ribs (12 pairs).
*They are elongated yet flattened bones that curve inferior and anterior from the thoracic vertebrae. Generally ribs 1-7 are connected to the sternum by their costal cartilages and are called true ribs, where ribs 8-12 are termed false ribs. Usually ribs 8-10 by means of their costal cartilage, join the costal cartilage immediately above, whereas ribs 11 and 12 are free and are known as floating ribs.

*In general ribs increase in length from rib 1 -7 then decrease in length again to rib 12.
*The ribs also become progressively oblique from ribs 1-9 and then less slanted through to rib 12.

Question 39

Rib 1

Answer 39

The first rib is short and forms part of the thoracic inlet. The head articulates with the T1 vertebra and the neck lies behind the apex of the lung. The flat upper surface faces superiorly and may present a groove for the subclavian artery and the lower trunk of the brachial plexus, anterior to which is the tubercle for the scalenus anterior muscle.
*There is also a groove for the subclavian vein.

Question 40

Rib 2

Answer 40

is longer than the first is curved and articulates with T1 and 2 vertebral bodies and presents a tuberosity for the serratus anterior muscle

Question 41

*Ribs 3-9

Answer 41

are known as typical ribs and have features in common. Each has a head, neck and shaft. The head presents 2 articular surfaces – one for the corresponding vertebral body and one for the vertebra immediately superior. The junction of the neck and shaft is marked by a tubercle, which articulates with the transverse process of the corresponding vertebra. The shaft is the weakest part. The concave, inner surface of the shaft is marked inferiorly by the costal groove, which give attachment to the internal intercostal muscle and shelter to the intercostal vein, artery and nerve. The ribs ossify from a primary centre for the shaft and secondary centres for the head and tubercle.

Question 42

Ribs 10 -12. rib 10

Answer 42

Usually articles with the 10th thoracic vertebra only. Rib 11 articulates only with the T11 vertebra and has an indistinct tubercle, angle and costal groove. Rib 12 articulates with T12 and is small, slender and variable in length.
*Some people can lack 1 or 2 pairs of these floating ribs, while some can have a 3rd pair

Question 43

Ribs: Costal cartilages

Answer 43

The costal cartilages are comprised of hyaline cartilage which can ossify. They fit into depressions in the anterior ends of the ribs and the upper 7/8 articulate with the sternum. The costal cartilage imparts resiliency to the chest wall. They often become partly ossified later in life.

Question 44

Normal variants – costal cartilage calcification

Answer 44

Calcification of the costal cartilages tends not to be radiographically apparent in most healthy patients younger than 35 years. Be- fore that age, calcification of the costal car- tilages may be associated with chronic renal failure, thyroid disease, autoimmune disor- ders, and chondrosarcoma [2]. The normal patterns of calcification differ between males and females, usually appearing as peripheral parallel lines in males (Fig. 4A) and as cen- tral, globular clumps in females.

Question 45

What are cervical ribs?

Answer 45

Definition: Accessory ribs that arise from the 7th cervical vertebra.

Prevalence:
Occur in ~0.5% of the population.
Typically bilateral, but often asymmetric.
More common in females.

Symptoms: Usually asymptomatic, but can cause thoracic outlet syndrome by compressing:
Brachial plexus (nerve issues).
Subclavian artery/vein (vascular problems).

Question 46

What is a Bifid rib?

Answer 46

Bifid rib is a congenital abnormality of the anterior chest wall occurring in about 1% of the population. The sternal end of the rib is cleaved into 2.

Question 47

What is the diaphragm and its structure?

Answer 47

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.
*At the front, fibres insert into the xiphoid process and along the costal margin. Laterally muscle fibres insert into ribs 6-12. in the back, muscle fibres insert into T12 and 2 appendages – the right and left crus, and descend and insert into L1 and L2.

There are 2 lumbocostal arches, a medial and lateral on either side.
*The left an right crura are tendons that blend of the anterior longitudinal ligament of the vertebral column.
*The central tendon of the diaphragm is closer to the front than the back of the thorax so the posterior muscular fibres are the longer.
*The diaphragm is primarily innervated by the phrenic nerve.

Question 48

Diaphragm: How is blood received

Answer 48

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.

Question 49

Function of the diaphragm

Answer 49

–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.