Pleural Diseases in the Horse

Question 1

What is the definition of pleura?

Answer 1

Thin membrane of connective tissue plus a layer of mesothelial cells

Question 2

What is parietal pleura?

Answer 2

Lining of the thoracic cavity

Question 3

What is visceral pleura?

Answer 3

Covers the outer surface of the lungs and other thoracic structures

Question 4

What is the Pleural cavity?

Answer 4

the space between the parietal and the
visceral pleura (right and left). Normally just a potential space
with a small volume of pleural fluid lubricating the surfaces

Question 5

What is the mediastinum?

Answer 5

Central thoracic area between the two lungs and the two pleural cavities

Question 6

What may the pleural space fill with potentially?

Answer 6

• Fluid (transudate, exudate)
• Blood
• Chyle
• Air

Question 7

What disease is rare in horses?

Answer 7

Pleural disease with transudate

Question 8

How might pleural disease with transudate arise?

Answer 8

• Increased venous pressure
• Congestive heart failure
• Decreased plasma colloidal pressure
• Hypoproteinaemia

Question 9

What disease is extremely rare in horses?

Answer 9

Pleural disease with chyle
- generally follows blunt trauma

Question 10

What is the composition of modified transudate?

Answer 10

mild increase in cells (5-20x109/L, mixed cell types, <90% neutrophils,
possibly exfoliated neoplastic cells), and mild increase in protein (20-30 g/L)

Question 11

What two things are typical of thoracic neoplasia?

Answer 11

• Blockage of lymphatic drainage
• Inflammatory response to a neoplasm

Question 12

Give three examples of pleural disease with modified transudate?

Answer 12

• lymphoma
• melanoma
• mesothelioma

Question 13

What is the most common reason for pleural effusion?

Answer 13

Exudate- - moderate to marked increase in neutrophils (some
degenerate) and protein in pleural fluid

Question 14

What four things result from bacterial infection

Answer 14

pneumonia (pleuropneumonia)
* penetrating thoracic trauma
* metastatic abscess (e.g. Strep equi equi, Rhodococcus equi)
* oesophageal rupture

Question 15

What are the four steps of pleuropneumonia?

Answer 15

1. Begins as a bacterial infection of the airways (septic bronchitis)
2. Infection and inflammation spreads to the pulmonary parenchyma
3. Infection and inflammation spreads to the visceral pleura
4. Exudation into the pleural cavity

Question 16

What is the main risk factor for pleuropneumonia?

Answer 16

Long distance transport/ head tied up= poor mucocilliary clearance

Question 17

Name four risk factors for pleuropneumonia

Answer 17

1. Head tied up = poor mucocilliary clearance
2. Enclosed airspace= poor air hygeine
3. Mixing with other horses= spread of pathogens
   4.

Question 18

What does pleuropneumonia ocassionally follow?

Answer 18

• severe and strenuous exercise (stress?)
• general anaesthesia (stress, tracheal intubation?)
• external wounds
• aspiration pneumonia (e.g. post-“choke”)
• oesophageal rupture

Question 19

What are the clinical signs of pleuropneumonia?

Answer 19

often not a clinically obvious
diagnosis
* fever, dullness
* shallow and rapid breathing
pattern?
* chest pain (elbows
abducted, walks slowly,
grunting, may appear
“colicky”?)
* possibly a soft cough (N.B.
chest is painful)

Question 20

Name 5 diagnostic tests for pleuropneumonia

Answer 20

1. Clinical Picture
2. Blood Sampling
3. Endoscopy
4. Ultrasonography
5. Pleurocentesis

Question 21

What does a pleuropneumonia endoscopy usually show?

Answer 21

Usually simply shows white-creamy-yellow
exudate
* >95% neutrophils
* Sometimes shows orange exudate or frank
bleeding
* Culture from trachea is more successful
than culture from the pleural fluid
* Often mixed oropharyngeal bacteria
* Streptococci
* Enterobacteriacea
* Anaerobes
* Klebsiella sp. especially
destructive and persistent

Question 22

What does a pleuropneumonia ultrasonography usually show?

Answer 22

• Points of ultrasound penetration that represent pleural roughening and inflammation
• Larger areas of lung consolidation
• Pleural effusion
• Pleural fibrin

Question 23

What is the medical therapy needed for pleuropneumonia?

Answer 23

• Antimicrobials
• NSAIDS
• Anti-fibrogenesis
• Fibrinolytics

Question 24

Name three other causes of pleural exudate

Answer 24

• Penetrating trauma
• Aspiration following oesophageal obstruction (choke)
• Oesophageal rupture