Page 175 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

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

Cats: In the normal cat, the TDS consists of a single duct animal’s prognosis and treatment. Identification of an
on the left side of the caudal mediastinum. In the middle of underlying cause, such as heart disease or cranial media-
VetBooks.ir of cats. In the cranial mediastinum, the duct is on the left resolve the chylothorax without the need for surgery. In
the mediastinum there are multiple ducts in a vast majority
stinal lymphoma, suggests a treatment plan that may
idiopathic cases, the clinician is left to treat the conse-
side of the oesophagus in 90% of cases and terminates at
the jugulosubclavian angle, the left external jugular vein or
the brachiocephalic vein. These variations in anatomy have quences of the disease (i.e. the chylous pleural effusion)
rather than its root cause.
important implications for the surgical approach when
considering thoracic duct ligation.
Clinical signs
Chylothorax can affect any breed of dog or cat. However,
Aetiology Afghan Hounds and Shiba Inu dogs, and Oriental breeds
Chylothorax remains an enigmatic disease in many dogs of cat, such as Himalayan and Siamese, may be predis-
and cats because of the difficulty in identifying a specific posed. Presentation to a veterinary surgeon (veterinarian)
cause and in defining an effective treatment. Previously, is usually precipitated by either dyspnoea, associated
many cases of chylothorax were presumed to be traumatic with the chylous pleural effusion, or persistent coughing.
in origin, with chylous fluid thought to leak from a ruptured Coughing may be due to the pleural effusion or caused by
TDS. However, many cases had no history of major a disease process underlying the chylothorax, such as
trauma, and experimentally the TDS in normal dogs heals cardiomyopathy or thoracic neoplasia. Other clinical signs
rapidly after deliberate transection. Congenital cases have can include anorexia, lethargy and weight loss. There is a
been described but these are also rare. great variability in the duration of clinical signs recognized
In the majority of dogs and cats, chylothorax is asso- by owners.
ciated with dilatation of the TDS (lymphangiectasia) and
leakage. Experimentally, ligating the cranial vena cava Physical examination
close to the right atrium can produce TDS lymphangi -
ec tasia, so conditions that increase pressure in the cranial Findings usually include an increased respiratory rate and
vena cava have the potential to cause chylothorax. TDS variably muffled lung and heart sounds. Poor body condi-
lymphangiiectasia and leakage can also occur secondary tion may reflect debilitation associated with the loss of fats
to physical obstruction caused by neoplasia. Hence, and proteins into the pleural space.
chylothorax has been associated with:
Diagnostic imaging
• Congenital heart disease (e.g. tetralogy of Fallot,
tricuspid dysplasia, cor triatriatum dexter) Radiography: Thoracic radiographs should be taken
• Heart base tumours unless positioning the animal causes worsening respir-
• Cardiomyopathies atory difficulty. In this instance, thoracocentesis (see
• Mediastinal lymphosarcoma or thymoma Operative Technique 12.1) is performed before radio-
• Foreign body or fungal granulomas graphy, as both a diagnostic and a therapeutic measure.
• Heartworm disease Thoracic radiographs should be taken in any animal with
• Cranial vena caval thrombosis. chronic coughing not responding to symptomatic treat-
ment, as this can be the only clinical sign associated with
Chylothorax can also occur associated with more chylothorax in some instances. Opposite lateral radio-
generalized lymphatic abnormalities such as intestinal graphs of the thorax allow better evaluation of the right
lymphangiectasia and lymphangioleiomyomatosis. and left lung fields. DV positioning is less stressful for the
The role of the pericardium in the aetiology of chylo- animal than VD. Radiographs will often show only non-
thorax has also received attention. Theoretically, restriction specific signs of pleural effusion, such as rounding of the
of the right atrium and ventricle by restrictive or effusive lung margins, interlobar fissure lines and separation of
pericardial diseases could increase the pressure in the cra- the lungs from the thoracic wall. Conditions underlying
nial vena cava and contribute to chylothorax. Whilst there chylothorax may be visible on thoracic radiographs,
are many dogs with significant pericardial effusions that depending on the severity of the pleural effusion. Caudal
have no associated chylothorax, pericardectomy is reported displacement of the cardiac silhouette and widening of the
as an effective treatment for chylothorax in some cases. cranial mediastinum may indicate a cranial mediastinal
The ‘cause and effect’ association between lung lobe mass. Enlargement of the cardiac silhouette may indicate
torsion and chylothorax remains unclear. Some authors list pericardial effusion or cardiac disease. Marked consolida-
lung lobe torsion as a potential cause of chylothorax. Whilst tion of one lung lobe with a prominent, aberrantly located
torsion of the right middle lung lobe could be argued to air bronchogram may indicate lung lobe torsion. Lung
cause obstruction of, or increased pressure in, the TDS, it lobes that have a persistent shrunken, rounded appear-
is equally possible that a chylous effusion may ‘float’ and ance, even after removal of pleural effusion, may be
mobilize the right middle lung lobe, facilitating torsion. affected by fibrosing pleuritis (Figure 12.9). Scarring and
Regardless of these arguments, it is important to realize contraction of the lungs’ visceral pleura appears to occur
that these two conditions can occur simultaneously. in response to chronic pleural effusion.
In many instances, a search for diseases underlying
chylothorax yields no definitive answer. The condition in Ultrasonography: This is useful for evaluating the heart and
these animals is thus classified as ‘idiopathic’. Some of mediastinum for diseases that might cause chylothorax. In
these cases may eventually reveal an identifiable under ying many instances, identified masses can be biopsied or
l
cause, such as microscopic neoplasia obstructing the TDS, aspirated with ultrasound guidance, providing material for
which is undetectable without a surgical or post-mortem a definitive diagnosis. Ultrasonography can also be used to
biopsy. In spite of these frustrations, the investi gation for evaluate the hilus of a suspected lung lobe torsion and
underlying causes is important when considering both an the cranial vena cava for evidence of thrombosis.

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