Chylothorax Flashcards

Chylothorax

Basics

• Definition:
  • Accumulation of chyle in the pleural space.
  • Chyle: Triglyceride-rich fluid from intestinal lymphatics that empties into the venous system (usually cranial cava/jugular vein) in the thorax.
  • Pseudochylous effusion: Effusion with less triglycerides and more cholesterol compared to serum, but appears fatty grossly.
  • Thoracic lymphangiectasia: Tortuous, dilated lymphatics found in animals with chylothorax.
  • Fibrosing pleuritis: Pleural thickening leading to constriction of lung lobes; severe cases result in marked restriction of ventilation; commonly associated with chylothorax and pyothorax.

Pathophysiology

• Alteration of flow through the thoracic duct (TD) leading to leakage of chyle.
  • Can be related to increased pressure or permeability in TD or venous obstruction downstream.
  • Can be caused by diseases/processes that increase systemic venous pressure at the entrance of the TD to the venous system.
• Cardiac causes:
  • Pericardial disease, cardiomyopathy, heartworm disease, other causes of right-sided heart failure, thrombosis around pacing lead wire.
• Noncardiac causes:
  • Neoplasia (especially mediastinal lymphoma in cats), lung lobe torsion, diaphragmatic hernia, venous granuloma, venous thrombus.
• Rare TD rupture/trauma:
  • Surgical (thoracotomy), nonsurgical (e.g., hit by car).
• Idiopathic cases are considered most common.

Systems Affected

• Respiratory: Reduced lung expansion.
• Systemic signs: Can be present secondary to respiratory distress (e.g., decreased appetite, weight loss).

Genetics

• Unknown.

Incidence/Prevalence

• Unknown.

Geographic Distribution

• Worldwide.

Signalment

• Species: Dog and cat.
• Breed Predilections:
  • Dogs: Afghan hound and Shiba Inu.
  • Cats: Oriental breeds (e.g., Siamese and Himalayan).
• Mean Age and Range:
  • Any age affected.
  • Cats: More common in older cats, could indicate an association with neoplasia.
  • Afghan hound: Develop when middle-aged.
  • Shiba Inu: Develop when young (<1–2 years of age).
• Predominant Sex: None identified.

Signs

• General Comments:
  • Signs depend on the rate of fluid accumulation and volume of pleural effusion.
  • Usually not exhibited until marked impairment of ventilation.
  • Many patients appear to have the condition for prolonged periods before diagnosis.
• Historical Findings:
  • Tachypnea and respiratory difficulty.
  • Coughing: Can be present for months before examination, likely due to lung compression associated with pleural effusion.
  • Lethargy.
  • Anorexia and weight loss.
  • Exercise intolerance.
• Physical Examination Findings:
  • Vary with cause of effusion.
  • Muffled heart and lung sounds ventrally.
  • Increased bronchovesicular sounds, particularly in dorsal lung fields.
  • Pale mucous membranes or cyanosis.
  • Arrhythmia.
  • Heart murmur.
  • Signs of right-sided heart failure (e.g., jugular pulses, ascites, hepatomegaly).
  • Decreased compressibility of anterior chest—common in cats with a cranial mediastinal mass.

Causes

• Cranial mediastinal masses: Lymphoma, thymoma.
• Cardiac disease: Heartworm, cardiomyopathy, pericardial disease, congenital diseases.
• Lung lobe torsion.
• Venous obstruction: Granuloma, thrombi.
• Congenital abnormality of TD.
• Cardiac or thoracic surgery.
• Idiopathic: Most common cause.

Risk Factors

• Unknown.

Diagnosis

• Differential Diagnosis: Other causes of pleural effusion—neoplasia, pyothorax, heart failure, feline infectious peritonitis (FIP).
• CBC/Biochemistry/Urinalysis:
  • Often normal.
  • Lymphopenia and hypoalbuminemia can be found; hyponatremia and hyperkalemia sometimes noted due to fluid shifts with repeat thoracocentesis.
• Other Laboratory Tests: Heartworm testing.
• Fluid Analysis:
  • Classified as an exudate.
  • Color depends on fat content from diet and presence of concurrent hemorrhage—usually milky white and opaque, but can appear serosanguinous and range from yellow to pink.
  • Protein content varies, and high lipid content will make refractive index inaccurate.
  • Total nucleated cell count usually <10,000 cells/\muL.
  • Fluid triglycerides higher compared to serum.
  • Fluid cholesterol lower compared to serum.
• Cytology:
  • Place sample in an EDTA tube to allow cell count to be performed.
  • Initially, cytology comprises primarily small lymphocytes, neutrophils, and macrophages containing lipid.
  • Chronic effusions contain fewer lymphocytes due to continued loss and more non-degenerate neutrophils due to inflammation from multiple thoracocenteses or irritation of pleural lining by chyle.
  • Atypical lymphocytes suggestive of underlying neoplasia.
• Imaging:
  • Thoracic Radiography:
    • Two to four views if patient is stable.
    • Dorsoventral view associated with less stress than ventrodorsal view in animal with respiratory difficulty.
    • Repeat radiographs after thoracocentesis to assess for underlying causes of effusion or evidence of fibrosing pleuritis; if collapsed lung lobes do not appear to reexpand after pleural fluid is removed or if respiratory distress persists with only minimal fluid present, suspect underlying pulmonary parenchymal or pleural disease (e.g., fibrosing pleuritis).
  • Ultrasonography/Echocardiography:
    • Should be performed before thoracocentesis if patient is stable—fluid acts as an acoustic window, enhancing visualization of thoracic structures.
    • Assess for underlying causes—detect abnormal cardiac structure and function, pericardial disease, and mediastinal masses.
  • CT Lymphangiography:
    • Can quantify TD branches more accurately than standard radiographic lymphangiography.
    • In dogs, percutaneously inject 1–2 mL of nonionic contrast material into mesenteric lymph nodes using ultrasound or CT guidance.
    • Acquire helical thoracic CT images before and after injection of contrast media.
    • Can document location and character of TD and its tributary lymphatics; likely useful for surgical planning.
• Pathologic Findings:
  • Lymphatics (including TD) difficult to identify at necropsy.
  • Fibrosing pleuritis—lungs appear shrunken; pleural layers (visceral and parietal) are diffusely thickened.
  • Fibrosing pleuritis—characterized histologically by diffuse, moderate to marked thickening of the pleura by fibrous connective tissue with moderate infiltrates of lymphocytes, macrophages, and plasma cells.

Treatment

• Appropriate Health Care:
  • Dyspneic animal: Immediate thoracocentesis; removal of even small amounts of pleural effusion can markedly improve ventilation.
  • Identify and treat the underlying cause, if possible.
  • Medical management: Usually treated on outpatient basis with intermittent thoracocentesis as needed based on clinical signs (see Medications).
  • Chest tubes: Place only in patients with suspected chylothorax secondary to trauma (very rare), in cases with rapid fluid accumulation, or after surgery.
  • Surgery if medical management does not resolve the problem in 2–3 months (see Surgical Considerations); some clinicians believe earlier intervention is better to avoid potential for development of restrictive pleuritis.
• Nursing Care:
  • Patients undergoing multiple thoracocenteses can rarely develop electrolyte abnormalities (hyponatremia, hyperkalemia) that may need to be corrected with fluid therapy.
  • Thoracocentesis: Perform under aseptic conditions to reduce risk of iatrogenic infection; antibiotic prophylaxis generally unnecessary if proper technique is used.
• Activity: Patients will usually restrict their own exercise as pleural fluid volume increases or if they develop fibrosing pleuritis.
• Diet:
  • Low fat: Potentially decreases the amount of fat in the effusion, which would improve the patient’s ability to resorb fluid from the thoracic cavity; not a cure; may help in management by facilitating reabsorption.
  • Medium-chain triglycerides are transported via the TD in dogs and are no longer recommended.
• Client Education:
  • Inform client that no specific treatment will stop the effusion in all patients with the idiopathic form of the disease.
  • Inform client that the condition can spontaneously resolve in some patients after several weeks or months.
• Surgical Considerations:
  • TD Ligation and Pericardiectomy:
    • Recommended in patients that do not respond to medical management.
    • The duct usually has multiple branches in the caudal thorax where ligation is performed; failure to occlude all branches results in continued pleural effusion.
    • Always perform in conjunction with lymphangiography; methylene blue injected in the mesenteric lymph node greatly facilitates visualization and complete occlusion of all branches.
    • Thickening of the pericardium can prevent formation of lymphaticovenous communications—perform pericardiectomy simultaneously with TD ligation; reports of up to 100% success rate when both techniques are performed; second surgery can be necessary if all branches are not occluded.
    • Video-assisted thorascopic surgery for thoracic duct ligation and pericardiectomy is reported to have similar success rates to thoracotomy (86%).
  • Other:
    • Success rates of 83–88% reported for cysterna chyli ablation in combination with TD ligation.
    • Salvage procedures for recurrence after TD ligation include cisterna chyli and TD glue embolization, pleuroperitoneal or pleurovenous shunts, or placement of a PleuralPort®.
• Medications:
  • Drug(s) of Choice:
    • Rutin 50–100 mg/kg PO q8h; believed to increase macrophage removal of proteins, which promotes absorption of fluid; complete resolution of effusion appears to occur in some patients; further study is required to determine whether resolution occurs spontaneously or in response to this therapy.
    • Somatostatin analog (octreotide)—a naturally occurring substance that inhibits gastric, pancreatic, and biliary secretions and prolongs gastrointestinal transit time, decreases jejunal secretion, and stimulates gastrointestinal water absorption; in traumatic chylothorax, reduction of gastrointestinal secretions may aid healing of the TD by decreasing TD lymphatic flows; resolution of pleural fluid has occurred in dogs and cats with idiopathic chylothorax in which octreotide has been administered, but the mechanism is unknown; octreotide (Sandostatin®; 10 \mug/kg SC q8h for 2–3 weeks) is a synthetic analog of somatostatin that has a prolonged half-life and minimal side effects.
  • Contraindications: Cardiac disease or neoplasia—treat the underlying disease rather than the effusion (other than heartworm disease in cats where TD ligation may be beneficial while the heartworm infection clears).
• Follow-Up:
  • Patient Monitoring:
    • Monitor for signs of recurrence of pleural effusion (tachypnea, labored breathing, respiratory distress)—perform thoracentesis as needed.
    • Periodically reevaluate for several years to detect recurrence.
  • Possible Complications:
    • Fibrosing pleuritis.
    • Iatrogenic infection with repeated thoracocentesis—important to use aseptic technique.
  • Expected Course and Prognosis:
    • Can resolve spontaneously or after surgery.
    • Untreated or chronic disease—can result in severe fibrosing pleuritis and persistent dyspnea.
    • Euthanasia—frequently performed in patients that do not respond to surgery or medical management.
  • Miscellaneous:
    • Associated Conditions: Diffuse lymphatic abnormalities (e.g., intestinal lymphangiectasia, hepatic lymphangiectasia, pulmonary lymphangiectasia, and chylous ascites)—may be noted; may worsen the prognosis.
    • Age-Related Factors: Young patients may have a better prognosis than old animals because of the association of neoplasia with advanced age.
• Abbreviations:
  • FIP = feline infectious peritonitis.
  • TD = thoracic duct.