Page 86 - Problem-Based Feline Medicine

78 PART 2 CAT WITH LOWER RESPIRATORY TRACT OR CARDIAC SIGNS

Pathogenesis controversy whether this finding represents a cause
and effect of lymphatic hypertension.
Chyle is the lymphatic fluid being transported from the
● Thoracic trauma is a less common cause of thoracic
abdominal organs to the prehepatic circulation. It con-
duct rupture, although this has been documented.
tains lipid-rich products such as chylomicrons, and
● Chronic chylothorax is irritating to the pleura and
grossly it is pink to milky white. Protein content may
may cause fibrosing pleuritis and pericarditis.
vary, and measurement may be interfered with by the
● New evidence suggests this secondary fibrosing
presence of the lipids. Cells are primarily small lym- pericarditis may lead to increased right-sided pres-
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phocytes, and the count (TNCC) is < 10 × 10 /L.
sures and decreased lymphaticovenous drainage,
The thoracic duct is the cranial continuation of the cys- resulting in diminished drainage of the thorax, and
terna chyli, the major lymphatic structure draining the persistence of the chylothorax.
abdominal organs. The thoracic duct passes through
the diaphragm at the aortic hilus and proceeds cra-
nially in the mediastinum dorsal to the thoracic aorta and Clinical signs
ventral to the azygous vein. It terminates cranially at the
Chylothorax generally occurs in middle-aged cats,
lymphaticovenous junction at the thoracic inlet, either
possibly more common in purebreds.
into left jugular, subclavian, or brachiocephalic veins.
Here the lymphatic fluid from the entire body, except the Vague signs of depression and lethargy, often for
right side of the face, the right pectoral limb, and the greater than 1 month, are common.
right thoracic wall, which drain into the right lymphatic
Tachypnea, dyspnea and the ventilation pattern typical
duct, re-enters the venous circulation.
for pleural space disease are present. This involves
The rate of lymph flow through the thoracic duct in cats increased chest wall excursion, often with the head and
has been estimated at 2 ml/kg/hour, increasing up to neck extended, but very little airflow present. Dyspnea
10-fold after a high-fat meal. Rapid accumulation of may be reported as acute in onset. Dyspnea is often
several hundreds of milliliters of fluid can occur with worsened in lateral recumbency and cats are reluctant
obstruction of or leakage from lymphatic drainage. to lie in lateral recumbency.
Chylous effusion in cats is most often idiopathic. Heart sounds are muffled but become more apparent
The most commonly known causes are associated after the chest tap and are generally normal.
with increased lymphatic hypertension from conges-
Abnormal heart sounds such as murmurs, gallops or
tive heart failure or obstructive neoplasia (see sec-
arrhythmias may be present if the chylous effusion is
tions under Cardiomyopathy or Mediastinal masses in
associated with congestive heart disease, but are gener-
this chapter).
ally absent in idiopathic chylous effusion.
Increased systemic venous pressure associated with
Coughing may be present from pleural irritation.
dilated cardiomyopathy and rarely heartworm diseases
may result in lymphatic hypertension and, occasionally
chlyothorax. Diagnosis
Mediastinal neoplasia, especially lymphosarcoma and
Clinically there are signs of pleural effusion and muf-
thymoma are most common neoplasias associated with
fled heart sounds.
chylothorax.
Thoracocentesis should be performed prior to radiogra-
Occasionally thrombus formation associated with an
phy in the severely dyspneic patients, both as an emer-
indwelling jugular catheter results in chylothorax.
gency treatment and a diagnostic procedure.
Idiopathic chylous effusions are associated with tho- ● The typical effusion is grossly chylous with milky-
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racic duct disease. white to pink fluid. Cell count is usually <1 × 1 /L
● Thoracic duct lymphangiectasia, demonstrated via and is largely lymphocytes, unless the effusion is
contrast lymphangiography, is the most common chronic in which case large numbers of neutrophils
finding in primary chylothorax in cats. There is and macrophages may be present.