cytology of fluids and less cellular lesions

fluids

» Fluids may be within cavities

» Fluid filled lesions may also be seen eg cysts

» Fluid cytology may refer to flush/wash samples eg BAL

collection of fluids

» Plain tubes (no gel) are required for culture

» For cytology EDTA may preserve cellularity better

• But there will always be some cell swelling in vitro

» Fresh smears made at time of sampling provide the best cytologic evaluation

classification of cavity fluids

» Two systems in use

» (1) Exudate, modified transudate, transudate

» (2) Exudate, protein-poor transudate; protein-rich transudate

» May also have haemorrhagic effusion- not generally included in the above classifications

» Lymphorrhagic effusions may also be considered separately (often associated with chylous effusions)

» Multiple processes can be involved in development of effusions

Exudate

» Effusion produced by increased vascular permeability to plasma proteins because of inflammation

» High cellularity (> 5 x109/L or > 7 x109/L )

» High protein (>20g/L or >30g/L)

transudate

» Effusion produced by passage of fluid or solute through a membrane due to changes in hydraulic or oncotic pressure

» ‘Pure’ transudate- low cellularity (<1.5x 109/L), low protein

» Modified tranusduate- ‘pure’ transudate modified by the addition of protein or cells

» Protein-poor transudates

• Marked hypoalbuminaemia

• Most commonly seen with hepatic cirrhosis or PLN

» Protein rich transudates

• Increased plasma hydraulic pressure in the liver or lungs – often due to venous congestion

• Most commonly seen with congestive heart failure or portal venous hypertension

evaluation of body fluids - gross appearance

Evaluation of body fluids

» Cell count

» Protein value

» Where relevant

» Cholesterol and Triglycerides (compared to serum)

» Creatinine +/- urea

» Bilirubin

Fluid Preparations

» May use direct smear preparations

» May also use concentrated preparations

• Centrifugation of sample and sediment preparation

• Cytospin preparation

» Microscopic evaluation of the cells

synovial fluid

» Normal cellularity is very low

» Few mononuclear cells

» Rare neutrophils

Chronic Inflammation

» Macrophages

» With trauma also seen increased macrophages and a few neutrophils

» Blood also present

Synovial Fluid Neutrophilic inflammation

» Low numbers of nucleated cells

• Trauma

• Local inflammation

» High cellularity (> 3x10⁹/L)

• Canine – immune mediated polyarthritis (most common- expect multiple joints affected)

• Equine -Probable sepsis (usually only one joint affected)

• Systemic immune mediated disease uncommon in the horse

septic neutrophilic inflammation

» Bacteria may be hard to identify on the smears in synovial fluid

» Growth of bacteria obtained from synovial fluid may be inhibited in the laboratory- the mechanism unclear

blood contamination

» May also increase neutrophil count which may mask inflammation

» If CBC is normal the number of neutrophils added by mild blood contamination are low and shouldn’t significantly alter the cellularity of the fluid

» If in doubt check blood smear/CBC

peritoneal fluid

• Low cellularity with approximately equal numbers of neutrophils and mononuclear cells/macrophages

• However neutrophils may be predominant population in healthy horses

peritoneal and pleural fluid

» Mesothelial cells line these cavity spaces

» Mesothelial cells can exhibit marked atypia when active/reactive – such as in response to fluid presence, or the cause of the fluid presence.

» Unreactive sheets of cells have a fishscale appearance

Septic Peritonitis vs contamination or enterocentesis

• With ongoing sepsis neutrophils are degenerate and bacteria are intracellular

• With contamination bacteria are extracellular and neutrophils may not appear degenerate

• Enterocentesis appears similar to contamination, but may have other organisms such as protozoa present

bacterial contamination

septic peritonitis

ruptured gut

Haemoperitoneum

• Erythrophagia or haem pigment noted in macrophages

• Often >5% PCV

— Trauma

— Neoplasia

— Idiopathic

Uroperitoneum

• Observe calcium carbonate and oxalate crystals in abdominal fluid in horses

• Other species may have different crystals- or none at all

• May have a neutrophilic inflammatory response

neoplasia

• Not all neoplasms will exfoliate into the fluid

• Careful that you have not aspirated spleen if thinking lymphoma

respiratory wash

» Normally cellularity is low

» Small amount of mucus with a few macrophages and respiratory epithelial cells

septic inflammation

inflammation

» Curshmann’s spirals

» Inspissated mucus from bronchioles

» Seen with chronic inflammation or irritation

Haemorrhage

» Macrophages containing hemosiderin (hemosiderophages)

» Can be seen with EIPH – Equine Exercise Induced Pulmonary Haemorrhage

Special Stains-Prussian blue

Parasites

» ‘Lungworm’ may be seen in BALs

» Angiostrongylus vasorum in the dog

» Aelurostrongylus abstrusus in the cat

Eosinophilic Inflammation - lung

» Feline allergic airway disease (FAAD) _ (feline asthma)

» Eosinophilic bronchopneumopathy in the dog

» Precise aetiology not elucidated

» Appears allergic in nature

» Marked eosinophils in lung washes

CSF (cerebrospinal fluid)

» Low cellularity (<5 cells/L in the dog, <8 cells/L cat)

» Low Protein ( <0.25g mg/L cisternal; <0.45g/L for lumbar)

» May identify inflammatory processes

» Occasionally may observe neoplastic cells

Seroma, Hygroma, Synovial Cyst, Apocrine Cyst

» There are a number of cutaneous lesions that may be fluid filled and poorly cellular.

» Hygromas will generally occur at pressure points/joints

» Synovial cysts will often have a background similar to synovial fluid

» Apocrine cysts are cutaneous, superficial

» ANY tumour can have a cystic area and a solid area- so if you can palpate a fluid filled space and a thickened tissue area ensure you have sampled both

Keratin containing lesions

» There are a number of benign cutaneous masses that are keratin containing

» These will often present with keratin material or cholesterol crystals only when aspirated.

summary

» Precise interpretation of fluids may depend upon the site of collection

» Inflammation/Inflammatory responses may be clearly identified on fluid samples and in some sites or disease processes may provide clear indication of the underlying cause of the effusion

» Neoplasia may also be identified

» For cytology EDTA tubes AND fresh smears are preferable

» For culture plain tubes are required.