CXR

Question 1

CXR

Densities

Answer 1

Photons shot at a receptor.

Things that absorb more photons appear more opaque.

From most to least radiopaque:

1. Metal
2. Bone
3. Soft tissue
4. Fat
5. Lung
6. Air

Question 2

PA View

Answer 2

Beam coming from the posterior and going to the anterior.

Heart size is the most accurate.

Question 3

AP View

Answer 3

Beam coming from anterior and going posterior.

For patients unable to stand for CXR.

Heart appears bigger b/c closer to the beam.

Question 4

Lateral View

Answer 4

By convention, beam on the right, detector on the left.

Question 5

CXR

Reading Checklist

Answer 5

Which view i.e. PA, AP, lateral?

Develop a systematic search pattern and always look at every CXR in the same way.

Do not stop at the first abnormality found.

1. Lungs
2. Trachea & right paratracheal stripe
3. Pleural margins
4. Cardiomediastinal silhouette
5. Hila
6. Pulmonary vasculature
7. Diaphragm
8. Costophrenic sulci
9. Abdomen
10. Bones
11. Soft tissues of chest wall and neck

Question 6

Obscured Margin

Answer 6

When two soft tissue densities lie in apposition, their borders will become indistinguishable or obscured.

Question 7

Silhouette Sign

Answer 7

When two soft tissue densities overlap in an image but are seperated by air, their borders will still be visible.

Question 8

Lung Anatomy

Answer 8

• Right lung
  
  • 3 lobes ⇒ upper, middle, lower
  • 2 fissures ⇒ oblique “major” fissure, horizontal “minor” fissure
    
    • Minor fissure can be seen on PA/AP view if there is an abnormality
• Left lung
  
  • 2 lobes ⇒ upper and lower
  • 1 fissure ⇒ oblique “major” fissure

Question 9

Pulmonary Fissures

Lateral View

Answer 9

Can see b/l oblique fissures and horizontal fissure on the right.

Question 10

Atelectasis

Definition

Answer 10

Collapse of alveoli.

• Can affect part of all of a lung
  
  • Lobar
  • Segmental
  • Sub-segmental

Question 11

Atelectasis

Causes

Answer 11

• Asthma
• Mucous plugging
• FB aspiration
• Iatrogenic ⇒ ETT inserted into one mainstem bronchus, collapsing the other
• Obstructive lesions ⇒ ex. carcinoma
• Compression from concomitant pleural effusion

Question 12

Lobar Atelectasis

Answer 12

Radiological sign ⇒ volume loss

• Shift of fissures
• Hemi-diaphragm elevation
• Compensatory hyperinflation of other lobes

Question 13

Pneumonia

Answer 13

Infection of the lung with pus in the alveoli or interstitium.

• Types:
  
  • Lobar PNA
  • Interstitial PNA
• Associated with inflammation of the lung parenchyma
  
  • Bacterial ⇒ alveolar (lobar) consolidation ± pleural effusions
  • Viral ⇒ increased interstitial markings
• Radiographic improvement lags behind clinical improvement
  
  • F/U CXR in 6 weeks if patient clinically improving

Question 14

Round Pneumonia

Answer 14

• Typically seen in kids
• Likely due to absence of collateral air-communicating pathways ⇒ pores of Kohn, canals of Lambert
  
  • Limits spread of infection

Question 15

Complications of PNA

Answer 15

1. Pleural effusion
2. Empyema
3. Abscess

Question 16

Complicated PNA

Work-up

Answer 16

Typically requires cross-sectional imaging:

Ultrasound or CT

Question 17

Lung Abscess

Answer 17

Collection of pus in the lung.

• Factors associated with higher mortality
  
  • Abscesses > 4 cm
  • Nosocomial infections
  • Abx resistant strains
• Predisposing conditions:
  
  • Aspiration
  • Intubation
  • Bronchiectasis
  • Bronchial obstruction
  • Hematogenous spread
  • Immunocompromised

Question 18

Trachea

Answer 18

Normally found in the midline.

Abnormalities:

Tube placement

Tension pneumothorax

Question 19

Trachea

Lateral View

Answer 19

Question 20

Trachea

Tube Placement

Answer 20

Question 21

Pneumothorax

Answer 21

Air trapped within the pleural cavity.

Question 22

Tension Pneumothorax

Answer 22

Signs of tension PTx:

• Depressed/inverted hemidiaphragm
• Contralateral shift of mediastinum and trachea
• Expansion of spaces between ribs

Question 23

Pleural Effusion

Answer 23

Fluid within the pleural cavity.

CXR: Complicated PNA with pleural involvement.

Question 24

Empyema

Answer 24

Pus within the pleural cavity.

• Usually arises from PNA w/ associated parapneumonic effusions.
• 3 stages:
  
  • Exudative
  • Fibropurulent
  • Organizing
• Usual organism ⇒ Strep. pneumoniae
• To evaluate using CXR:
  
  • Take left and right lateral views
  • If there is no shifting i.e. looks about the same ⇒ likely stuck and empyema

Question 25

Cardiomediastinal Silhouette

Answer 25

Heart is normal in size if it can fit in one hemi-thorax. Beware of AP view.

Question 26

Cardiomegaly

Answer 26

**General term used to describe an enlarged heart.** * Encompasses dilated and hypertrophic etiologies * If cardiac silhouette is larger than the diameter of a hemithorax ⇒ heart is enlarged

Question 27

Pneumomediastinum

Answer 27

Air in the mediastinum.

Question 28

Pulmonary Vasculature Normal

Answer 28

Question 29

Pulmonary Vaculature Congestion

Answer 29

**Increased caliber of pulmonary vasculature.** * _Etiologies_ * Volume overload in a patient with a normal heart * Vascular shunt ⇒ left to right * _Appearance_ * Bunch of grapes * Cephalization * Upper vessels enlarged

Question 30

Normal Radiation Exposure

Answer 30

* Background radiation ⇒ 3 mSv/yr * Radon * Cosmic rays * Radioactive material in our homes * Smoking 1 ppd = 53 mSv/yr

Question 31

Radiation Dose

Answer 31

* 2-view CXR ⇒ 0.2 mSv * Abdominal/Pelvis CT ⇒ 10 mSv * MRI or US ⇒ no radiation

Question 32

Effects of Radiation

Answer 32

* Radiation exposure is cumulative over lifetime * Linear No-Threshold Model * Long term biological damage caused by ionizing radiation directly proportional to dose * Children more susceptible