Thoracic imaging 1 Flashcards
What are some indications for thoracic imaging?
Coughing Dyspnoea Regurgitation Cardiac disease Tumour hunt Trauma Weight loss Chest wall abnormalities
Which diseases may have normal thoracic radiographs?
- Acute viral pneumonia
- Acute and chronic tracheobronchitis
- Lungworm
- Upper airway disease
What are some key radiographic technique points for the thorax
- Prevent rotation
- Wedges under sternum
- Assess costo-chondral junctions and where articulate with spine
- Keep in sternal recumbency
- Always take DV first
If using GA for thoracic radiographs what must you be aware of?
Beware of GA atelectasis – lung collapse due to the weight of the mediastinum when lying in one position for prolonger periods
How are radiographs systematically inturpreted?
- Assess radiograph overall: quality, phase of respiration, body condition
- Systematic approach: many blind spots
- Normal or abnormal?
What are the effects of recumbency?
- Different positions of diaphragmatic crura in left vs right lateral
- 2 crura of the diaphragm converge on the left lateral, whereas they stay separate on the right
- Cardiac silhouette differs
How can the phase of respiration alter a thoracic radiograph?
- Lungs larger (and less opaque) on inspiration
- Heart looks relatively smaller during inspiration
How can body condition be assessed/affect thoracic radiographs?
- Wide mediastinum because fat is store here
- Fat can be visible below the cardiac silhouette
- Increased apparent opacity of lungs in fatter animals
Describe the basic anatomy of the lungs
4 right lobes: cranial, middle, caudal, accessory
2 Left lobes: cranial (split into cranial and caudal parts) and caudal
What colour does decreased opacity appear?
Darker
What needs to be interpreted if the thoracic radiograph is abnormal?
Is it decreased or increased opacity? Determine where this change is (thoracic/anatomical compartment involved) - Pleural space/thoracic wall - Mediastinum - Lungs
What is a cause of decreased opacity in the lungs, how does this affect a thoracic radiograph?
Pleural space: pneumothorax
- Air (lucency) within pleural space
- Retraction of lungs from thoracic margins (and lung atelectasis)
- Elevation of cardiac silhouette from sternum
How do you interpret a thoracic radiograph with increased opacity?
- Rule out artefacts (poor technique, obesity)
- Increased opacity often is the abnormality
- Increased fluid/cells and/or loss of air e.g. pyothorax, pneumonia, mass
How are the thoracic boundaries assessed?
- Normal sternum and spine
- Mass, gas or thickening of soft tissues
- Assess each rib individually: normal in number, shape, opacity, size and position (equidistant)
How would a thoracic wall mass appear different to a chest wall mass on a radiograph?
- Thoracic wall masses - often associated with rib changes
* Chest wall masses - may see extrapleural sign of parietal pleura wall bulging into thorax
Describe the appearance of a pleural space effusion on a radiograph
- Border effacement heart and diaphragm
- Pleural fissures of fluid between lung lobes
- Retraction of lung margins from chest wall
- May mask underlying pathology (masses)
What is the mediastinum and which structures does it contain?
Soft tissue envelope formed by the pleura that contains the following mediastinal structures:
- Trachea
- Oesophagus
- Heart and associated great vessels
- Lymph nodes (sternal)
How are mediastinum masses classified?
Classify according to location:
- Cranioventral – most common place
- Craniodorsal
- Caudovental/caudodorsal
- Central (perihilar)
Describe how assessment of the lungs on a thoracic radiograph is carried out
- Increased vs. decreased opacity
- What is lung volume?
- Distribution of lesions: Cranioventral, Caudodorsal, Diffuse, Multifocal, Focal
- Lung pattern approach; bronchial, alveolar, interstitial, vascular
What are the two basic mechanisms of decreased lung opacity?
- Increased gas
- Decreased soft tissues/fluid
If the decreased lung opacity is diffuse what are the possible causes?
- Artefact
- Hypovolaemia
- Hyperinflation
If the decreased lung opacity is focal what are the possible causes?
- Cavitatory lung lesion
- Emphysema
- Thromboembolism
Which conditions may cause apparent decreased lung opacity?
- Pneumothorax
- Pneumomediastinum
- Subcutaneous emphysema
How is lung volume assessed?
- Volume decrease/loss (collapse/atelectasis)
- Volume increase (swelling/mass)
Describe the effects of the lungs causing a mediastinal shift
Mass effect
- Tells us about LUNG volume not mediastinum
- Mass/swelling pushes the mediastinum away
- Collapse pulls mediastinum towards it
Cranioventral lung distribution indicated which causes?
- Pneumonia
- Haemorrhage
- Atelectasis
Generalised lung distribution indicated which causes?
- Haemorrhage
- Metastatic neoplasia
- Atelectasis
- Oedema
- Fibrosis
- Bronchitis
Caudodorsal lung distribution indicated which causes?
- Oedema
- Haemorrhage
- Atelectasis
What are the 4 anatomical components of a lung?
- Bronchi
- Blood vessels
- Interstitial tissue
- Alveolar air spaces
Lung patterns localise to these
Describe bronchial pattern of disease
- Increased visibility of bronchial walls (thickened or increased in opacity)
- “Tramlines” and “donuts”: longitudinal vs end on bronchial walls
What are the DDx for bronchial disease patterns
- Calcification (increased opacity)
- Chronic bronchitis
- Peribronchial cuffing
What are the different causes of chronic bronchitis?
- Allergic
- Irritant
- Parasitic
- Idiopathic
What are the different causes of peribronchial cuffing?
- Oedema
- PIE/EBP – pulmonary infiltrate with eosinophils
- Pneumonia
- (Neoplasia)
Define Bronchiectasis
Widening of the bronchi
Describe alveolar pattern of disease
- Cells+/- fluid replaces air in alveoli
- Increased lung opacity
- Border effacement of adjacent structures
- May see air bronchograms
- Lobar sign if entire lobe affected
What are the DDx for diffuse alveolar lung patterns?
- Pneumonia
- Oedema (non-cardiogenic/cardiogenic)
- Haemorrhage
What are the DDx for focal alveolar lung patterns?
- Pneumonia
- Oedema
- Haemorrhage
- Primary/secondary lung tumour
- Lobar collapse/atelectasis
- Infarct
- Lung lobe torsion
Describe interstitial pattern of disease
- Cells or fluid in interstitial tissue
- Most commonly artefactual: expiration, obesity, underexposure
- Genuine unstructured interstitial disease rare
- Blood vessels less distinctly seen
- Should not completely efface soft tissue structures
What are the DDx for diffuse interstitial lung patterns?
- Artefact
- “Ageing”
- Lymphoma
- Diffuse metastases
- Pneumonitis (viral, parasitic, metabolic, toxic)
- Disease in transition
What is the most common cause of a nodular interstitial pattern?
Secondary neoplasia
How is a nodular interstitial pattern assessed? How are nodules visualised?
- Small nodules can be easily missed
- Need to be 4-5mm in diameter and surrounded by aerated lung (dependent lung collapses) otherwise opacities may be too similar to see masses
