CXR & AXR

Question 1

Quantify the radiation dose of a CXR

Answer 1

Equivalent to 3 days of standard background radiation

Question 2

Why does the heart appear larger in the AP view

Answer 2

X-ray beam diverges as it travels - similar to a light beam - any object further from the film will cast a larger ‘shadow’

Question 3

What is adequate penetration

Answer 3

Ideally one should see the upper vertebral bodies down to approximately the fifth thoracic vertebral body through the mediastinum.

Question 4

What is normal CTR

Answer 4

< 50%

Question 5

What is the correct position of the ETT on CXR

Answer 5

4 cm above the carina

Question 6

Describe the normal movement of the ETT inside the trachea

Answer 6

Chin up = tip up ± 2 cm
Chin down = tip down ± 2 cm

Therefore correct placement 4cm above the carina will prevent extubation/vocal cord damage and endobronchial intubation

Question 7

Describe the correct placement of a tracheostomy tube

Answer 7

The tracheostomy tube should occupy 1/2 to 2/3 of the tracheal diameter

The tip of the tracheostomy tube should be centrally located within the trachea at the level of the 3rd thoracic vertebra

Question 8

What level is the carina

Answer 8

T4/T5 = same level as the sternal angle

Question 9

What is the ideal position for the tip of a central venous line

Answer 9

Ideal: mid SVC = tip should be just above the right main bronchus on CXR

Acceptable: brachiocephalic vein

Question 10

Where are the venous valves located relevant to subclavian and internal jugular central venous access. Why are these valves relevant

Answer 10

Near the first rib

Relevance: Should the tip of the catheter abut one of these valves –> impaired flow

Question 11

Why should the tip of a central venous catheter not lie within the right atrium

Answer 11

Risk of cardiac arrhythmia or perforation

Question 12

Describe the CXR appearance of a correctly positioned pulmonary artery balloon tipped catheter (Swan-Ganz)

Answer 12

Middle third of CXR about 5 cm from the midline

Question 13

Describe some of the risks related to a pulmonary artery ballon tipped catheter

Answer 13

1. Pulmonary infarction/thrombosis (tip left inflated)
2. Pulmonary thromboembolism (stasis from inflated tip)
3. Arterial rupture
4. Pseudoaneurysm formation (Pseudoaneurysm = only adventitia of vessel encloses the dilatation - intima and media excluded)

Question 14

Where should chest drain be placed in pneumothoraces

Answer 14

Anterosuperiorly (air collects in the least dependent part of the chest)

Question 15

Where should the chest drain be positioned in pleural effusion

Answer 15

Posteroinferiorly –> fluid collects in the most dependent parts of the thoracic cavity

Question 16

What is the definition of a widened mediastinum

Answer 16

Widened mediastinum: Definition: A mediastinum measurement of ≥8 cm or >1/3rd the transthoracic distance at the level of the aortic knob on a supine AP film.

Question 17

How can the radiological signs of pulmonary collapse be classified

Answer 17

DIRECT SIGNS
- Displacement of fissures
- Increased density of lobe
(outline of adjacent structures may be obscured)
- Crowded vessels of bronchi

INDIRECT SIGNS

• Elevated hemidiaphragm
• Mediastinum shift (trachea upper lobe collapse | heart in lower lobe collapse)
• Hilar displacement
• Compensatory hyperinflation of other lobes (more lucent)

Question 18

What are the causes of pulmonary consolidation

Answer 18

INFLAMMATORY INFILTRATE IN ALVEOLI
- Infection
Pulmonary infection (TB/bacterial)

- Non-infectious
Extrinsic allergic pneumonia
Eosinophilic pneumonia
Aspiration
Sarcoidosis

FLUID IN ALVEOLI
Pulmonary oedema
Trauma (contusion)
Pulmonary haemorrhage

TUMOUR IN ALVEOLI
Lyphoma
Bronchoalveolar cell carcinoma

Question 19

Distinguish the clinical and radiological appearance of:

• lobar pneumonia
• bronchopneumonia
• aspiration pneumonia

Answer 19

LOBAR
Consolidation confined to a single lobe of the lung
- Previous healthy patient
- Streptococcus pneumoniae

BRONCHO and ASPIRATION
Consiolidation is patchy and often perihilar with bronchial wall thickening
- Elderly/debilitated patients
- Gram negative organisms

Question 20

What type of organism causes cavitation on CXR

Answer 20

1. Staphylococcus aureus,
2. Gram negative organisms (especially Klebsiella),
3. anaerobes and
4. Mycobacterium tuberculosis

Question 21

How to distinguish between right middle and right lower lobe pneumonia

Answer 21

Right lower lobe pneumonia causes loss of clarity of the right hemidiaphragm

Question 22

How is left lingula lobar pneumonia distinguished from left lower lobe pneumonia

Answer 22

Distorted left heart border

Question 23

How is the mediastinum divided and what does each section contain

Answer 23

Anterior - thymus and fat
Middle - heart, GVs and hila
Posterior - Oesophagus, azygous vein, descending aorta

Question 24

What is extramedullary haematopeisis

Answer 24

Extramedullary hematopoiesis is when blood precursor cells typically found in bone marrow (erythroblasts, megakaryocytes, myeloid precursors) accumulate outside of the bone marrow.

Question 25

How can one tell if the mass is in the middle mediastinum versus anterior or posterior

Answer 25

The heart border will be distorted by a mass originating in the middle mediastinal compartment.

Question 26

What are the most common causes of pulmonary hypertension

Answer 26

Chronic lung disease
Multiple pulmonary emboli
Primary pulmonary hypertension
Left to right shunt (Septal defect)

Question 27

Classify the CXR and signs and symptoms related to severity of left ventricular failure

Answer 27

PCWP < 15 mmHg
No symptoms
Normal CXR

PCWP 15 -20
Exertional dyspnoea | PND | Basal crackles
CXR: Upper lobe diversion

PCWP 20 - 25
Dyspnoea at rest | Orthopnoea | Crackles and wheezes
CXR: Interstitial oedema (Septal lines, perihilar haze, Peri-bronchial cuffing | Reticular opacities | Small pleural effusions)

PCWP > 25
Severe dyspnoea | Pink frothy sputum | CRT > 2 s
CXR: Alveolar oedema (Air-space opacities in a perihilar ‘batwing’ distribution)

Question 28

List common causes of dilated bowel on AXR

Answer 28

Mechanical obstruction (Adhesions/Cancer)
Pseudo-obstruction
Paralytic ileus
Air swallowing (pain/asthma/BVM)

Question 29

What is the difference between pseudo-obstruction and paralytic ileus

Answer 29

Pseudo-obstruction is clearly limited to the colon alone, whereas ileus involves both the small bowel and colon. The right colon is involved in classic pseudo-obstruction, which typically occurs in elderly bedridden patients with serious extraintestinal illness or in trauma patients.

Question 30

What causes paralytic ileus

Answer 30

Postoperatively

Local inflammatory processes, e.g. pancreatitis or appendicitis

Trauma
Congestive cardiac failure
Renal failure
Debility
Infection

Question 31

How can small and large bowel dilatation be distinguished

Answer 31

Variable
Small Bowel
Colon

Distribution of dilated bowel
Central
Peripheral

Number of loops of dilated bowel
Many
Few

Diameter of dilated bowel
3-5 cm
5 cm +

Haustra
Absent
Present

Valvulae conniventes
Present in jejunum
Absent

Radius of curvature of dilated loops
Small
Large

Solid faeces
Absent
Present

Question 32

List the causes of mechanical bowel obstruction

Answer 32

Adhesions (75%)
Strangulated hernia (8%)
Small bowel volvulus
Strictures (inflammatory/radiation)
Extrinsic compression
Intrinsic lesions
- Gallstones
- Small bowel tumours