NORMAL RADIOLOGY OF THE THORAX

PLEURAL CAVITY ABNORMALITIES

Pleural fluid (pleural effusion)

Types

1. "Transudate"

2. Blood

3. Lymph

4. Exudate (pyothorax)

Signs

1. Homogeneous opacity in ventral thorax (frequently "scalloped" lung edges)

2. Partial/complete loss of heart/diaphragm shadow

3. Interlobar fissures seen (fluid between lung lobes)

4. Fluid in thoracolumbar recess in caudodorsal thorax (N.B. normal reflection of lungs in cats)

5. Fluid opacity between lungs and thoracic wall in VD/DV

Pneumothorax

Signs

1. Lucent space between the heart shadow and sternum

2. Lung lobes retracted from the thoracic borders, with no lung markings at the periphery

3. Increased lung opacity (collapse)

4. Film has an overall overexposed appearance

Beware:

1. Small lucent space between heart and sternum in deep-chested dogs at peak inspiration

2. Skin folds in DV/VD views

3. Fat between heart and sternum in fat dogs

MEDIASTINAL ABNORMALITIES

Mediastinal masses

These are more common in the cranial mediastinum, where they often cause dorsal (or ventral) displacement of the trachea and caudal displacement of the heart. Oesophageal dysfunction may occur with large masses.

LUNG PATTERNS

Most patterns are MIXED, with more than one of the following. We must deduce from the combinations what the underlying disease is.

Normal Lung Pattern

Alveolar pattern

Fluid accumulation, cellular infiltrates and lung collapse may cause this.

Types

1. Transudate

2. Blood

3. Exudate

4. Cellular

5. Collapse

Signs

1. Ill-defined ("fluffy") patches of increased opacity.

2. Ill-defined areas remain aerated (air alveolograms).

3. Bronchi become visible against increased opacity (air bronchograms). Beware parallel blood vessels, esp. over heart.

4. Lung lobar margins seen.

5. Blood vessels, heart and diaphragm become obscured.

6. Alveolar infiltrates are very labile and may change markedly over 24-48 hours.

Interstitial pattern

Types

1. Unstructured: ageing changes

fibrous healing or chronic disease

early oedema, haemorrhage or pneumonia

lymphoma/diffuse pulmonary metastasis

pneumonitis (e.g. viral, parasitic, uraemia, paraquat)

Beware: underexposed or partially expiratory films will mimic this pattern. Digital radiographs also show more marked interstitial markings than film.

Signs:

1. Diffuse increased lung opacity

2. Blood vessels, heart and diaphragm become unclear (but usually still visible)

3. Honeycomb, reticular, meshwork appearance

4. May be similar to alveolar, but less "fluffy"

N.B. Most unstructured interstitial patterns are incidental.

2. Miliary nodulation (2 - 5mm diameter rounded opacities):

metastatic neoplasm

pulmonary lymphoma

granulomatous PIE

Aelurostrongylus (cats)

TB

3. Evenly rounded, discrete multiple nodules (> 5mm diameter):

metastatic neoplasm

primary lung tumours

4. Solitary nodule (>5mm diameter.):

indistinct: focal pneumonia

...

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