Page 375 - Clinical Small Animal Internal Medicine

34 Pleural Effusion 343

mesenteric lymph node to highlight the thoracic duct, Hemothorax
VetBooks.ir has been utilized for over 30 years in veterinary medi- Hemothorax is defined as an exudative effusion in the pleu-
cine to guide surgical planning and assess postoperative
success. Mesenteric lymphangiography is an invasive
procedure as it requires an exploratory laparotomy and ral space with a PCV that is at least 25% of peripheral blood.
Iatrogenic hemorrhage during thoracocentesis should be
injection of contrast medium into a mesenteric lym- suspected if the sample contains platelets and lacks eryth-
phatic vessel or lymph node, followed by radiographs or rophagocytosis on cytology. In general, causes of hemotho-
CT under general anesthesia; therefore less invasive pro- rax can be divided into coagulopathic and noncoagulopathic.
cedures have since been developed for thoracic duct Anticoagulant rodenticide toxicity is the most common
imaging. More recent minimally invasive imaging cause of coagulopathic hemothorax in veterinary patients
modalities include percutaneous mesenteric lymphade- but disorders of primary hemostasis could also result in
nography, laparoscopic mesenteric lymphadenography, hemothorax. Reported noncoagulopathic etiologies include
percutaneous popliteal lymphangiography, and subcuta- neoplasia, thoracic trauma, lung lobe torsion, pancreatitis,
neous or submucosal lymphography, and CT has largely pulmonary parasitic disease (Spirocerca lupi, Dirofiliaria
replaced conventional radiography as the ideal imaging immitis, or Angiostrongylus vasorum), esophageal foreign
technique. body, and pulmonary infarction. Therapeutic thoracocen-
Surgical treatment is recommended if chylothorax is tesis should only be performed in patients with hemothorax
persistent despite medical therapy because chyle is if respiratory distress is present on physical examination
inflammatory and can cause severe fibrosing pleuritis because most of the blood will be reabsorbed once the
or pericarditis. Thoracic duct ligation at the entry underlying cause is treated. Coagulation tests should be
point of the duct into the thorax is the most com- performed prior to thoracocentesis and blood products
monly performed surgical technique for dogs and cats should be readily available. Fresh frozen plasma should be
with idiopathic chylothorax. The premise behind tho- administered to coagulopathic patients with hemothorax,
racic duct ligation is to create a stimulus for new lym- prior to or during therapeutic thoracocentesis, if this is
phaticovenous connections to the caudal vena cava or deemed necessary on patient evaluation. Thoracic ultra-
azygous vein outside the pleural space, thereby bypass- sound, echocardiography, and CT may be utilized to deter-
ing the thoracic duct and preventing intrathoracic mine the underlying cause along with standard blood tests,
flow of chyle. Surgical approach to the thoracic duct heartworm test, and fecal examination. Treatment is
can be through a caudal intercostal thoracotomy, par- directed at the underlying cause and emergency surgical
acostal or ventral midline celiotomy with transdia- treatment may be necessary in some dogs or cats that are
phragmatic extension, median sternotomy, or using nonresponsive to conservative management.
thoracoscopy.
Several adjunctive surgical procedures have been
combined with thoracic duct ligation in an effort to Bilothorax
increase success rate of treatment. Cisterna chyli abla-
tion was developed because hypertension within the Bilothorax is the accumulation of a nonseptic, exudative
cisterna chyli is thought to cause collateral lympathic effusion high in bilirubin within the pleural space and is rare
vessels to form around the thoracic duct ligation site. in both veterinary and human medicine. It has only been
Adjunctive subtotal pericardectomy is rationalized reported in a few veterinary patients, all of which had recent
because chronic chylous effusions can cause pericardi- hepatobiliary trauma (gunshot wound or penetrating
tis, which in turn can increase right‐sided venous pres- trauma) or biliary surgery. In one cat, the penetrating
sure and possibly impede chyle drainage from new trauma was iatrogenic; pleurobiliary fistulae occurred sec-
lymphaticovenous anastomoses. Other adjunctive or ondary to thoracotomy tube placement. The theorized
alternative procedures are thoracic omentalization to mechanism of bilothorax formation is from pleurobiliary
provide lymphatic drainage, pleurodesis to abolish the formation, with a presumptive diaphragmatic incongruity;
pleural space, and cisterna chyli and thoracic duct however, bile can also be carried across an intact diaphragm
embolization, with the latter being a salvage procedure by way of the lymphatic system. Diagnosis is confirmed if
if previous surgical attempts have failed. Surgical (con- the ratio of bilirubin in pleural fluid to serum is greater than
ventional or thoracoscopic) success rates vary between 1:1. Given the rarity of bilothorax, optimal treatment is con-
50% and 100% in dogs and 14.3% and 80% in cats. troversial. Medical management by placing thoracostomy
Persistence of chylous or nonchylous pleural effusion is tubes with frequent pleural fluid drainage is recommended
the most common surgical complication. If surgical to minimize bile pleuritis. If medical management fails, sur-
treatment fails, then implantation of an active pleurop- gical exploration is recommended. Bilothorax in dogs and
eritoneal shunt or PleuralPort device should be consid- cats appears to have a good prognosis, with a combined
ered to manage long‐term effusion. 100% survival rate of currently reported cases.