Page 402 - Small Animal Internal Medicine, 6th Edition

374 PART II Respiratory System Disorders

detecting persistent pulmonary lesions. Rooney et al. (2002) Fibrosing pleuritis and pericarditis can be associated with
recommended consideration for thoracotomy particularly in chylothorax. Cats, in particular, may develop fibrosing pleu-
VetBooks.ir dogs that have radiographic evidence of mediastinal or pul- ritis, which can interfere with normal expansion of the lungs
even after thoracocentesis. Inflammation and thickening of
monary lesions, or if Actinomyces spp. are identified in the
the pericardium could contribute to the further formation of
pleural fluid.
chylous effusion.
Prognosis
The prognosis for animals with pyothorax is fair to good if Clinical Features
it is recognized early and treated aggressively. Waddell et al. Chylothorax can occur in dogs or cats of any age. Afghan
(2002) reported a survival rate for cats of 66%, excluding Hounds and Shiba Inus appear to be predisposed to the
those that were euthanized before treatment. In their report, disorder. The primary clinical sign is respiratory distress
5 of 80 cats required thoracotomy. Boothe et al. (2010) typical of pleural effusion. Although the distress is often
reported a 1-year survival rate of 70% for dogs treated with acute in onset, more subtle signs have generally been present
chest tube drainage, with or without surgery, but only 29% for longer than a month. Lethargy, anorexia, weight loss, and
for dogs treated with intermittent thoracocentesis. However, exercise intolerance are common. In some cases, cough is the
in a study by Rooney et al. (2002) of 26 dogs, only 25% of only presenting sign.
dogs were successfully treated medically, whereas 78%
responded favorably to thoracotomy. One possible explana- Diagnosis
tion for the poor success of medical management in the latter Chylothorax is diagnosed by thoracic radiography and by
study is its geographic location in a region of the country identification of chyle through cytologic and biochemical
where grass awn migration is common. evaluation of pleural fluid obtained by thoracocentesis (see
Exploratory surgery is necessary to ensure complete reso- Chapter 23). Lymphopenia and panhypoproteinemia may be
lution of the problem in dogs or cats with foreign bodies in present in peripheral blood. The complication of fibrosing
the thoracic cavity. Radiolucent foreign bodies can be diffi- pleuritis is suspected when lung lobes have rounded borders
cult to find, however, and the prognosis for pyothorax sec- radiographically and the degree of respiratory compromise
ondary to them is more guarded. Long-term complications subjectively exceeds that expected from the amount of fluid
of pyothorax such as pleural fibrosis and restrictive lung in the pleural space.
disease are uncommon. Once chylothorax has been diagnosed, further diagnostic
tests are performed to identify potential underlying disease
(Box 24.1). These tests include thoracic ultrasonography;
CHYLOTHORAX echocardiography; microfilarial examination and adult
antigen testing for heartworm disease; and, in cats, the mea-
Etiology surement of thyroid hormone concentrations. Computed
Chylothorax is the accumulation of chyle within the thoracic tomography will be more sensitive than thoracic radiogra-
cavity. The chyle originates from the thoracic duct, which phy in identifying and characterizing localized disease and,
carries triglyceride-rich fluid from the intestinal lymphatics when performed with contrast, may identify venous throm-
and empties it into the venous system in the anterior thorax. boses. Lymphangiography can be used to identify lymphan-
This fluid also contains lymphocytes, protein, and fat-soluble giectasia, sites of obstruction, and, rarely, sites of leakage
vitamins. Thoracic duct rupture after thoracic trauma can from the thoracic duct. Lymphangiography is performed
result in transient chylothorax. However, most cases are not before surgical ligation of lymphatics is attempted.
the result of a ruptured duct. Possible causes of nontraumatic
chylothorax include generalized lymphangiectasia, inflam- Treatment
mation, and obstruction of lymphatic flow. Flow can be Thoracocentesis and appropriate fluid therapy are used to
obstructed for physical reasons, such as neoplasia, or as a stabilize dogs and cats with chylothorax, as needed, at pre-
result of increased venous pressures. sentation. Electrolyte abnormalities may be present. A con-
Chylothorax can be categorized as congenital, trau- certed effort is made to identify any underlying cause of the
matic, or nontraumatic. A congenital predisposition may chylothorax, so that it can be directly treated. Elimination
exist in animals in which chylothorax develops later in life. of the underlying problem may result in resolution of the
Traumatic events that induce chylothorax can be surgical chylothorax, although medical management (as described
(e.g., thoracotomy) or nonsurgical (e.g., being hit by a car). later for idiopathic chylothorax) is generally required for
Nontraumatic causes of chylothorax include neoplasia, par- several weeks or even months. The exception is chylothorax
ticularly mediastinal lymphoma in cats; cardiomyopathy, of traumatic origin, which generally resolves within 1 to
dirofilariasis, pericardial disease, and other causes of right- 2 weeks.
sided heart failure; central venous thromboses; lung lobe A routinely successful treatment for idiopathic chylotho-
torsion; diaphragmatic hernia; and systemic lymphangiecta- rax has not been established. Medical management is ini-
sia. No underlying disease can be identified in most animals, tially attempted because spontaneous remission occurs in
in which case idiopathic chylothorax is diagnosed. some cases. In the absence of resolution with medical therapy,