L22 Cardiothoracic Imaging

Question 1

Radiographs

Answer 1

• planar
• superimposition of shadows created when x-ray traverses body parts
• no depth
• a lot of information lost

Question 2

Chest X-ray evaluation

Answer 2

1. Name, date, label
2. Adequacy / Lung inflation: 10 post ribs, 6 anterior ribs (well inflated lungs —> more visible structures)
3. Penetration: retrocardiac, T-spine outline
4. Rotation: medial needs clavicles equi-distance from spinous process
5. Project: PA vs AP (size of heart, lung inflation since patient maybe supine)

Question 3

PA vs AP projection

Answer 3

PA:

• standard
• higher quality
• accurately assess heart size (less diffraction)
• medial edges of scapulae retracted laterally

AP:

• when PA not possible
• lower quality
• exaggerated heart size and mediastinal contour (more diffraction)
• medial edges of scapulae not retracted

Question 4

Pleural pressure distribution

Answer 4

Always negative

• superior pleural space —> most negative
• inferior pleural space —> least negative
• affected by gravity, weight of lungs and connective tissues

Question 5

Pneumothorax

Answer 5

• abnormal air collection within pleural space
• pleural pressure becomes homogeneous
• deflation of lung + less expansion of chest wall
• see outline of deflated lung
• outside of lung region —> appear dark (radiolucent because of air)
• more obvious in expiration x-ray film

—> impairs ventilation and haemodynamic stability (↓venous return —> ↓cardiac output)
—> symptoms depends on size of pneumothorax

Question 6

Tension pneumothorax

Answer 6

One-way valve: air only go in during inspiration, cannot go out during expiration
—> accumulation of pleural air
—> collapse of ipsilateral lung
—> exerting positive pressure on mediastinal and intrathoracic structures
—> mediastinal shift
—> compression of low-pressure vasculature + decrease in -ve pressure
—> ↓venous return, ↓cardiac output
—> life-threatening (requires chest drain)