Page 403 - Small Animal Internal Medicine, 6th Edition

CHAPTER 24 Disorders of the Pleural Cavity and Mediastinum 375

Although the benefit of dietary management has been
BOX 24.1 questioned, a low-fat, nutritionally complete diet is fed in
VetBooks.ir Diagnostic Tests to Identify Underlying Diseases in Dogs patients with good body condition. In humans medium-
chain triglyceride oil is absorbed directly into the blood-
and Cats With Chylothorax
Complete Blood Count, Serum Biochemical Panel, stream, bypassing the lymphatics, and can be used as a fat
supplement. Unfortunately, in dogs these triglycerides have
Urinalysis been shown to enter the thoracic duct. Studies have not been
Evaluation of systemic status performed in cats.
Medical management may be facilitated by the adminis-
Cytologic Examination of Fluid tration of rutin, a benzopyrone drug. Rutin has been used
Infectious agents in humans for the treatment of lymphedema. It is thought to
Neoplastic cells (especially lymphoma)
decrease the protein content of the effusion by affecting mac-
Thoracic Radiographs (After Fluid Removal) rophage function. The resorption of effusion may thereby be
Anterior mediastinal masses enhanced and fibrosis of the pleura minimized. The drug is
Other neoplasia available over the counter at health food stores. A dosage of
Cardiac disease 50 to 100 mg/kg given orally every 8 hours is recommended.
Heartworm disease Surgical management is considered if clinical signs have
Pericardial disease not improved within 1 to 3 months of medical therapy, or if
signs are intolerable. The recommended surgical manage-
Ultrasonography (Ideally, in the Presence of Fluid) ment of chylothorax includes thoracic duct ligation and peri-
Anterior mediastinum cardectomy, with or without ablation of the cisterna chyli.
Mass Thoracic duct ligation is technically difficult and ideally per-
Heart (echocardiography)
Cardiomyopathy formed by an experienced surgeon. Multiple ligations of the
Heartworm disease thoracic duct and its collaterals are performed. The ducts are
Pericardial disease identified by lymphangiography before surgery, and lym-
Congenital heart disease phangiography is repeated after ligation to assess the success
Other fluid densities adjacent to body wall of ligation. Pericardectomy is recommended at the time of
Neoplasia thoracic duct ligation and is associated with an improved
Lung lobe torsion outcome (Fossum et al., 2004). Ablation of the cisterna chyli
has also been reported to enhance success (McAnulty, 2011).
Heartworm Antibody and Antigen Tests Placement of pleuroperitoneal or pleurovenous shunts or
Heartworm disease mesh within the diaphragm to allow fluid to drain away from

Computed Tomography the pleural space has also been recommended for the man-
Often more sensitive than radiography or agement of chylothorax and should be considered if medical
ultrasonography and surgical treatment is unsuccessful. These drainage pro-
With contrast, to identify central venous thromboses cedures provide a route by which the leaking chyle can
reenter the circulation without producing the respiratory
Lymphangiography compromise associated with pleural effusion. Unfortunately,
Preoperative and postoperative assessment of thoracic drains often become nonfunctional within months of
duct placement.
Prognosis
The prognosis for chylothorax is fair, unless the chylothorax
surgical treatment that includes thoracic duct ligation and was traumatically induced or was the result of a reversible
pericardectomy is recommended. condition. Most studies report a positive response to surgical
Medical management consists primarily of intermittent intervention in the range of 50% to 80% of patients (Singh
thoracocentesis and a low-fat diet. Thoracocentesis is per- et al., 2012b). It is not possible to predict the contribution of
formed as needed on the basis of the owner’s observation of fibrosing pleuritis to clinical signs in cats with this complica-
increased respiratory rate or effort or decreased activity or tion. In cats with continued respiratory difficulties after reso-
appetite. Initially, thoracocentesis may need to be performed lution of effusion, decortication of the lung is considered.
every 1 to 2 weeks. The interval between thoracocenteses
will gradually lengthen if the chylothorax is responsive to
medical management. Ultrasound guidance of the needle NEOPLASTIC EFFUSION
during thoracocentesis is especially helpful in removing
pockets of chyle from the pleural cavity. By increasing the Neoplastic effusions resulting from mediastinal lymphoma
effectiveness of drainage, it can prolong the interval between are treated with radiation or chemotherapy (see Chapter 79).
thoracocenteses. Effusions caused by mesothelioma or carcinoma of the