Page 171 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

Non-septic exudates: These are characterized by high Bacteroides, Fusobacterium and Porphyromonas and the
protein levels. A major cause of this type of effusion is aerobes Actinomyces, Pasteurella, Escherichia coli and
VetBooks.ir this condition. A diagnosis of FIP is strongly supported by lates are similar to those identified from cats, with the
FIP; both pleural and peritoneal effusions often occur in
Streptococcus (Walker et al., 2000). These bacterial iso-
addition of Streptococcus and the enteric E. coli. In dogs,
finding a globulin concentration >32% of the total protein
(TP) concentration in the effusion. If the albumin compo-
bodies such as grass awns, penetrating wounds to the
nent is >48% or the albumin:globulin ratio of the effusion reported causes of infection include migrating foreign
is >0.81, FIP is unlikely (Lappin, 1998). Serum hyper- chest, neck or mediastinum, oesophageal perforations,
proteinaemia, with or without hypoalbuminaemia, is also a lung parasites, bacterial pneumonia with abscessation
common finding. and rupture, haematogenous or lymphatic spread from
other septic foci, spread from cervical or lumbar disco-
Septic exudates: These may be caused by: penetrating spondylitis, neoplasia with secondary abscessation and
thoracic injury; perforation of mediastinal structures or a iatrogenic contamination from thoracocentesis or thora-
lung abscess; migrating foreign bodies; haematogenous cotomy. The hunting and working breeds of dogs are
spread; or iatrogenic contamination (see Pyothorax). over-represented in most retrospective studies, and aspi-
ration of grass awns with subsequent migration through
Haemorrhagic effusion: A major cause of haemorrhage the respiratory tract is thought to play an important role
into the pleural cavity is thoracic trauma, such as fractured in the development of pyothorax in these breeds.
ribs or pulmonary parenchymal lacerations. A small amount
of haemorrhage is common after thoracic surgery and this Cats: The most common bacterial isolates from cats
may be marked if an intercostal vessel has been punctured with pyothorax are the anaerobes Peptostreptococcus,
during closure. An intrathoracic tumour or a coagulopathy Bacteroides, Fusobacterium, Porphyromonas and Prevotella
(e.g. anticoagulant rodenticide toxicity) may result in spon- and the aerobes Pasteurella and Actinomyces (Walker et al.,
taneous haemorrhage into the pleural cavity. Dyspnoea is 2000). Mixed populations of bacteria are often cultured from
usually relieved by thoracocentesis. Depending on the both cats and dogs. The most likely sources of the bacteria
severity of blood loss, patients may require supportive that cause pyothorax in cats are from the oral cavity of other
treatment with fluid therapy and possibly a blood trans- cats, transmitted through bite wounds to the chest, or envi-
fusion. Animals that have anticoagulant rodenticide toxicity ronmental contamination from penetrating thoracic injuries.
also require treatment with vitamin K as well as active clot- Other possibilities include bacterial pneumonia leading to
ting factors from fresh whole blood or fresh frozen plasma. lung abscessation and rupture, rupture or perforation of the
oesophagus, trachea or bronchi, migrating foreign bodies
Chylous effusions: These are the result of leakage of chyle (grass awns) or lung parasites, or iatrogenic contamination
from an abnormal TDS and may be primary idiopathic from thoracocentesis or thoracotomy. Cats from multi-cat
or secondary to mediastinal neoplasia, heart disease, dia- households have been found to be at an increased risk
phragmatic rupture, lung lobe torsion or other conditions. for the development of pyothorax (Waddell et al., 2002).
Chylothorax is a very challenging condition to manage Once bacterial infection enters the pleural cavity, the
(see below). release of inflammatory mediators causes increased perme-
ability of the endothelial lining of the pleural capillaries and
Neoplasia: Primary and metastatic thoracic neoplasia may impairment of lymphatic outflow. This results in accum-
produce variable types of pleural effusion by a number of ulation of fluid, protein and inflammatory cells in the
different mechanisms, such as inflammation of the pleura, pleural space. Increased protein concentration in the pleural
haemorrhage and obstruction of lymphatic drainage. fluid causes an increased oncotic pressure, favouring addi-
Cytological examination will reveal neoplastic cells in tional fluid movement out of the capillaries and into the
approximately 50% of animals with a neoplastic pleural pleural space.
effusion; thus, an absence of neoplastic cells on cytology
does not rule out neoplastic disease. Mediastinal lympho-
sarcoma may exfoliate lymphoblasts into pleural fluid. Clinical signs
Mesothelioma (neoplasia of the pleura) is usually character- Presentation of the cat or dog with pyothorax is often
ized by a severe pleural effusion and may also affect the delayed for weeks to months after the inciting incident.
pericardium, causing a pericardial effusion. It is particularly Penetrating thoracic injuries, such as bite wounds, are
difficult to differentiate between reactive and malignant often healed by the time respiratory compromise develops,
mesothelial cells on cytology. Thoracoscopic exploration making diagnosis of the underlying cause difficult or
and mediastinal/pleural biopsy is a reliable and effective impossible. Common clinical signs in cats include respira-
means of diagnosing mesothelioma that avoids an unnec- tory distress, depression, lethargy, pallor, anorexia and
essary thoracotomy. pain. In dogs, exercise intolerance, respiratory distress,
reluctance to lie down, anorexia, lethargy and cough are
common. Clinical presentation can vary widely, from mild
Pyothorax respiratory signs to collapse from severe septic shock.
Pyothorax is characterized by the accumulation of septic
purulent fluid within the pleural space. Other terms that Physical examination
have been used to describe pyothorax include empyema
and purulent pleuritis. It has been described in both dogs Findings usually include varying degrees of respiratory
and cats, but is more common in cats. distress: increased respiratory effort, tachypnoea, dull
lung sounds ventrally with harsh sounds dorsally and
orthopnoea (breathing with the head and neck extended
Aetiology and elbows abducted, and remaining standing or in sternal
Dogs: The most common bacterial isolates from dogs recumbency) may all be present. Signs of septic shock,
with pyothorax are the anaerobes Peptostreptococcus, such as hyperthermia or hypothermia, tachycardia (or, in

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