The etiology of chylothorax is often not identified. Although trauma is listed as a potential cause in some sources, there
is no evidence that it would be responsible for persistent chylothorax. Causes included R-CHF, thoracic lymphangiectasia,
generalized lymphangiectasia, cranial mediastinal masses, fungal granulomas, venous thrombi, or congenital abnormalities of
the thoracic duct.
Breed predispositions include the Afghan hound (middle-aged), Shiba Inu (<1 year of age), and Oriental cat breeds.
Suggested medical therapy typically includes low-fat diets, thoracocentesis as needed, and Rutin (50-100 mg/kg TID PO). The
success of any one of these is questionable. Spontaneous resolution may occur without therapy. Rutin is a benzopyrone extracted
from plants. Its mechanism of action is unknown but it is suspected to reduce leakage of fluid from blood vessels, increase
proteolysis in extravascular sites, and enhance macrophage phagocytosis of chyle.
Suggested surgical therapy includes thoracic duct ligation with pericardiectomy. Complete ligation of the thoracic duct is
difficult without mesenteric lymphangiography. This author (Harkin) believes that continuous pleural evacuation following
surgery is important for guaranteeing success in addition to pericardectomy and TD ligation. Palliative procedures have also
been developed (pleuroperitoneal shunting) but are often fraught with complications and high expense.
In their study on thoracic duct ligation with concurrent cisterna chyli ablation (Hayashi K, Sicard G, et al. Cisterna chili
ablation with thoracic duct ligation of chylothorax: results in eight dogs. Vet Surg 2005;34:519-523.), the authors stated
that the goal of TD ligation is to block the flow of chyle to the area of leakage and result in the formation of new lymphaticovenous
anastomoses within 5-14 days to permanently divert chyle from the leaking thoracic duct and thoracic cavity. They point out
that TDL reportedly results in complete resolution 50-60% of the time. This failure could be related to development of collateral
lymphatics that bypass the ligature, failure to ligate all channels of thoracic duct, or ligation rostral to site of leakage.
The authors proposed that ablation of the CC (the cisterna chyli is an elongated saccular reservoir receiving lymph from the
lumbar and mesenteric lymphatic trunks that then empties into the thoracic duct at the level of the dorsal diaphragm) would
prevent recurrence of chylothorax. They looked retrospectively at 8 dogs with idiopathic chylothorax, three which had received
Rutin to no avail. One dog never resolved and was euthanized at 2 months; 1 dog had effusion for one month, then no additional
effusion for 4 months when it died suddenly; and 6 dogs had good long-term outcome with no additional fluid accumulation.
Whether CCA made the difference in these dogs is unknown without a comparison population of TDL alone. The efforts made to
identify all branches of the TD may have had the most significant contribution to success.
In their evaluation of pleuroperitoneal shunts (Denver shunt) (Smeak DD, Birchard SJ, McLoughlin MA, et al. Treatment of
chronic pleural effusion with pleuroperitoneal shunts in dogs: 14 cases (1985-1999). J Am Vet Med Assoc 2001;219:1590-1597.)
the authors noted short term complications of obstruction from tube kink, infection around external pump (2), pump chamber
dislodgement from thorax, pain on pumping, pump obstruction, owner compliance (2), and acute collapse just after discharge
(1). The long-term complications included pump obstruction (3), marked abdominal distension (3), pump dislodgement (1), pyothorax
(1), peritonitis (2), pleural compartmentalization (1), and owner compliance (1). Three dogs were reported not to have long-term
complications, although one was euthanized because rate of fluid accumulation exceeded rate at which it could be removed and
in one dog fluid accumulation stopped 6 weeks after removal of thymoma. Given the expense of the shunt itself (>$800), failure
to resolve fluid accumulation, and complications, I would not recommend this procedure to any client.
In this author's opinion, concurrent TDL and pericardiectomy are the preferred surgery. In one study (Fossum TW, Mertens
MM, Miller MW, et al. Thoracic duct ligation and pericardectomy for treatment of idiopathic chylothorax. J Vet Intern Med
2004;18:307-310.), in which 10 dogs and 10 cats with idiopathich chylothorax were treated (TDL and PC were performed simultaneously
in 13; PC was performed 2 and 9 months later in 2 dogs; 1 dog and 1 cat had PC without TDL; in 2 the PC was performed after
TDL elsewhere and one had repeated TDL; and other combinations of the above...) pleural fluid accumulation resolved in 10/10
dogs and 8/10 cats. Fibrosing pleuritis was evident in 5 cats and 1 dog. Decortication was performed in 2 cats, both of
which developed persistent post-op pneumothorax (resolved in both).