Chylothorax is a rare but complex disorder in domestic animals. Etiolo
gies include neoplasia, fungal infections, heartworm infestation, card
iac disease, thrombosis of the cranial vena cava, and congenital anoma
ly of the thoracic duct. Most cases of chylothorax in dogs and cats ar
e idiopathic. Positive contrast lymphangiography on dogs and cats with
chylothorax consistently reveals extensive lymphangiectasia of medias
tinal and pleural lymphatics. Reported treatment modalities for chylot
horax in animals include removal of the etiologic agent, such as a med
iastinal tumor, thoracic duct ligation, and implantation of active or
passive drainage devices such as a pleuroperitoneal shunt. Thoracic du
ct ligation has been most successful in our experience, but continued
study is needed since treatment failures are common.