Analysis of body cavity effusions

Question 1

Hydraulic pressure

Answer 1

Within vessels - drives fluid out

Question 2

Oncotic pressure

Answer 2

Within vessels - pulls fluid back into vessels

Question 3

Normal volumes of body cavity fluid (small animals)

Answer 3

<15ml in peritoneal cavity
<3ml in pleural cavity

Question 4

Normal fluid protein concentration in body cavity fluid (small animals)

Answer 4

should be <25 g/L (normally <20 g/L)

Question 5

Normal fluid nucleated cell count in body cavity fluid (small animals)

Answer 5

normally <3.0x10^9 cells/L

Question 6

Normal cells found in body cavity fluid (small animals)

Answer 6

Predominantly macrophages and lymphocytes, with low numbers of neutrophils and mesothelial cells.

Erythrocytes should not normall be present but can see iatrogenic contamination at time of sampling

Question 7

Mesothelial cells

Answer 7

Have characteristics of epithelial cells except that they can be seen in clusters of as individual cells.

They can appear similar to macrophages, however in some cases they can be recognised by the presence of a ‘fringed’ cytoplasmic border and/or a pink glycocalyx ‘halo’ around the cytoplasm.

Question 8

Normal volume of body cavity fluid in horses

Answer 8

10-100ml of peritoneal fluid
<8ml of pleural fluid

Question 9

Protein concentrations of body cavity fluid in horses

Answer 9

Up to 35g/L

Question 10

Nucleated cell count of body cavity fluid in horses

Answer 10

up to 12x10^9/L

Question 11

Effusion

Answer 11

the accumulation of fluid in a body cavity or space.
Effusions can occur in the pleural, peritoneal or pericardial spaces.

Question 12

Ascites

Answer 12

A fluid that accumulates in the peritoneal/abdominal cavity

Question 13

Causes of effusions

Answer 13

Increased vascular hydraulic pressure

Decreased vascular oncotic pressure

Increased vascular permeability (e.g. in inflammation)

Decreased lymphatic drainage (e.g. obstruction)

Leakage of visceral contents (urinary bladder, gall bladder, intestines)

Question 14

Classifications of effusions

Answer 14

Transudate (protein poor)
Transudate (protein rich)
Exudate

Question 15

Classifications of effusions (more broad)

Answer 15

Lymphorrhagic
- chylous
- non-chylous

Haemorrhagic

Secondary to leakage of bile or urine

Question 16

What tube should you use for body cavity effusions?

Answer 16

Some in an EDTA tube - for cytology and fluid protein determination

Some in a plain tube - for culture (EDTA is bacteriostatic)

Question 17

Fluid nucleated cell count of a protein poor transudate

Answer 17

<5 x 10^9/L

Question 18

Fluid protein concentration of a protein poor transudate

Answer 18

<25g/L

Question 19

Fluid nucleated cell count of a protein rich transudate

Answer 19

<5 x 10^9/L

Question 20

Fluid protein concentration of a protein rich transudate

Answer 20

> 25 g/L

Question 21

Fluid nucleated cell count of an exudate

Answer 21

> 5 x 10^9/L

Question 22

Fluid protein concentration of an exudate

Answer 22

Usually >25 g/L

Question 23

Most common diseases associated with protein poor transudates

Answer 23

Protein losing nephropathy (protein loss in urine due to glomerular disease)

Marked hepatocellular dysfunction (e.g. cirrhosis)

Question 24

Causes of protein poor transudates

Answer 24

Severe hypoalbuminaemia (<15 g/L) - interstitial fluid protein concentration is low so transudate is low in protein

Likely that it only happens without production of increased globulins and increased lymphatic drainage - rapid decrease in albumin or no compensatory mechanism

Question 25

Most common cells in a protein poor transudate

Answer 25

tend to contain very few cells (often <1.5x10^9/L) which are predominantly macrophages, neutrophils and mesothelial cells.

Question 26

Less common causes of protein poor transudate

Answer 26

Protein losing enteropathy (intestinal losses due to diarrhoea) Reduced lymphatic drainage (obstructive diseases of the lymphatic vessels and lymph nodes (e.g. neoplasia)

Question 27

In which species is it rare to have a pathological protein poor transudate?

Answer 27

Cats, horses, cattle

Question 28

What are protein rich transudates normally associated with?

Answer 28

Increased vascular hydraulic pressure. If oncotic pressure, capillary permeability and lymphatic drainage remain unaltered, then this will lead to a net increase in the movement of fluid out of the vasculature and into the interstitium. The resultant fluid protein concentration is dependent on interstitial fluid protein concentration, which is highest in the liver and intestines.

Question 29

Most common diseases associated with protein rich transudates

Answer 29

Congesetive heart failure Portal hypertension

Question 30

Less common causes of protein rich transudates

Answer 30

Secondary to neoplasia, FIP, or leakage of lymphatic fluid (lymphorrhagic effusions)

Question 31

Cells seen in protein rich transudates

Answer 31

Tend to contain low numbers of cells (<5.0x10^9/L) which are predominantly macrophages, neutrophils and mesothelial cells. In cats, low numbers of small lymphocytes may also be seen.

Question 32

Causes of exudates

Answer 32

Form due to increases in the capillary permeability that occur in response to inflammation. Inflammatory mediators (such as histamine, leukotrienes and bradykinins) that are released from inflamed tissues will increase capillary permeability, thus allowing the exudation of protein rich fluid from the plasma. Inflammation also leads to migration of leukocytes from the blood to the tissues (chemotaxis) through the now more permeable capillary walls.

Question 33

Cells found in exudates

Answer 33

High numbers of nucleated cells (>5.0x10^9/L but often much higher than this) that are usually predominantly neutrophils.

Question 34

Assessment of neutrophils in exudates

Answer 34

Look for signs of degenerative changes in the neutrophils - increases suspicion for bacterial infection

Question 35

Other (non-neutrophil) cells in exudates

Answer 35

Usually contain lower numbers of macrophages and lymphocytes. The mesothelial cells can also appear ‘reactive’. Mesothelial cells can show marked dysplastic changes in response to inflammation, therefore it is not uncommon to see many mesothelial cells with some criteria of malignancy within exudative effusions. It can be very difficult (or impossible) to differentiate between neoplastic cells and reactive mesothelial cells within exudates on cytology.

Question 36

Septic exudates

Answer 36

Often have very high nucleated cell count (mostly neutrophils). Bacteria is often seen

Question 37

Causes of septic peritonitis

Answer 37

Migration of foreign bodies or direct inoculation, or perforation of the GI tract/uterus

Question 38

Clinical signs of septic peritonitis

Answer 38

Usually clinically very unwell Depressed, collapsed, pyrexic Cats sometimes have mild clinical signs

Question 39

Pyothorax

Answer 39

Leads to increased respiratory rate and effort

Question 40

Causes of non-septic exudates

Answer 40

Sterile inflammatory reactions associated with FIP, pancreatitis, leakage of bile (unless bacterial cholangitis involved), or neoplasms

Question 41

Bile peritonitis

Answer 41

Caused by leakage of bile from the gall bladder or biliary tract, can be suspected if yellow-green bile pigment and crystals are seen within the fluid on cytology. Confirmation can be made by a documentation of a fluid bilirubin concentration that is >2x that of the serum

Question 42

Exudate caused by pancreatitis

Answer 42

Causes a localised or generalise non-septic peritonitis leading to the formation of exudative effusion Measurement of a fluid lipase activity that is >2x above that of the serum is suggestive of pancreatitis as a cause of the effusion

Question 43

Exudate cause by FIP

Answer 43

Body cavity effusions caused by immune complex vasculitis Classically have very high fluid protein concentration (>45g/L) but relatively loe nucleated cell count (1-30 x 10^9/L, but often <8) Effusions tend to contain a greater proportion of macrophages as well as non-degenerate neutrophils

Question 44

Neoplastic effusions

Answer 44

Usually classified as protein rich transudates or exudates based on increased nucleated cell counts, may be low protein transudates Check for the presence of neoplastic cells DIagnosis based in finding increased numbesr of cells demonastrating numerous criteria of malignancy in the abscence of inflammation

Question 45

Most common types of neoplastic effusion

Answer 45

Lymphoma - high numbers of large lymphocytes Carcinoma - if epithelial cells are demonstrating numerous criteria of malignancy are present

Question 46

Lymphorrhagic effusions

Answer 46

Form when there is leakage of lymphatic fluid Usually exudates but can be protein rich transudates if not many lymphocytes May contain lipids - can falsely increase protein concentration Main determinant is the presence of a predominant population of small lymphocytes

Question 47

Chylous effusions

Answer 47

A type of lymphorrhagic effusion Chylomicron rich lymphatic fluid Originates from lymphatic vessels in pathway between small intestine and thoracic duct Chylomicrons make them appear grossly milky or pink Long standing chylous effusions also contain increased numbers of macrophages In cats they can also be associated with eosinophils

Question 48

Non-chylous effusions

Answer 48

A type of lymphorrhagic effusion Lymphatic fluids not rich in chylomicrons Originate from lymphatic vessels that are not in the pathway between small intestine and thoracic duct

Question 49

How to confirm a chylous effusion

Answer 49

Measurement of the fluid triglyceride concentration (chylomicrons contain large amounts of triglycerides). A fluid triglyceride concentration >1.1mmol/L, particularly if the serum triglyceride concentration is <0.5x that of the fluid, is diagnostic for a chylous effusion.

Question 50

Causes of chylous effusions

Answer 50

Cardiac disease Neoplasia Diaphragmatic hernia Lung lobe torsion FIP Trauma (e.g. to thoracic duct) Iatrogenic (e.g. surgical ligation) Idiopathic (especially in cats)

Question 51

Causes of non-chyous effusions

Answer 51

Cardiac disease Neoplasia

Question 52

Heamorrhagic effusions

Answer 52

Usually exudates (if predominantly blood) or protein rich transudates Primary determinant is the presence of high PCV or HCT Pericardial effusions are often haemorrhagic in origin (idiopathic or neoplasia) Confirmed by finding haemosiderin or haematoidin laden macrophages Presence of erythrophagia is suggestive, as is red cells without platelets on the smear (blood from iatrogenic contamination should contain platelets)

Question 53

Uroperitoneum - effusion

Answer 53

Sterile urine present within the abdomen will induce mesothelial irritation and inflammation therefore effusions caused by urine leakage are often classified as protein rich transudates or exudates.

Question 54

Cytology of uroperitoneum

Answer 54

Only thing that can confirm is the possible pressence of urine crystals (e.g. struvite)

Question 55

What would make you suspect uroperitoneum?

Answer 55

- history of dysuria or stranguria - no palpable bladder - free fluid in abdomen - Increased serum creatinine and K+

Question 56

How can you confirm uroperitoneum?

Answer 56

Measurement of the fluid potassium and creatinine concentration. If the fluid potassium and creatinine concentration is >2x that of the serum, then the fluid is confirmed to be urine.