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Basics ⬇

Basics

Definition

  • Accumulation of chyle in the pleural space.
  • Chyle-triglyceride-rich fluid from the intestinal lymphatics that empties into the venous system in the thorax.
  • Pseudochylous effusion-effusion that contains less triglycerides and more cholesterol compared to serum.
  • Thoracic lymphangiectasia-tortuous, dilated lymphatics found in many animals with chylothorax.
  • Fibrosing pleuritis-condition in which pleural thickening leads to constriction of the lung lobes; when severe, results in marked restriction of ventilation; can be caused by any chronic pleural exudate but is most commonly associated with chylothorax and pyothorax.

Pathophysiology

  • Alteration of flow through the thoracic duct leading to leakage of chyle-can be related to increased pressure or permeability in the thoracic duct or venous obstruction downstream.
  • Can be caused by any disease or process that increases systemic venous pressure at the entrance of the thoracic duct to the venous system.
  • Cardiac causes-pericardial disease, cardiomyopathy, heartworm disease, other causes of right-sided heart failure.
  • Non-cardiac causes-neoplasia (especially mediastinal lymphoma in cats), lung lobe torsion, diaphragmatic hernia, venous granuloma, venous thrombus.
  • Less commonly thoracic duct rupture/trauma-surgical (thoracotomy), non-surgical (e.g., hit by car).
  • Idiopathic most common.

Systems Affected

  • Respiratory-due to reduced lung expansion.
  • Systemic signs can be present secondary to the 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 hounds and Shiba Inus
  • 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 hounds-develop when middle-aged.
  • Shiba Inus-develop when young (<1–2 years of age).

Predominant Sex

None identified

Signs

General Comments

  • Signs will depend on the rate of fluid accumulation and volume of pleural effusion.
  • Usually not exhibited until there is 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 the 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 the 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 thoracic duct.
  • Cardiac or thoracic surgery.
  • Idiopathic-most common cause.

Risk Factors

Unknown

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

Other causes of pleural effusion-neoplasia, pyothorax, heart failure, 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 will depend 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/µL.
  • 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 is comprised of primarily small lymphocytes, neutrophils, and macrophages containing lipid.
  • Chronic effusions contain less 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-pleural effusion.
  • Dorsoventral view associated with less stress than ventrodorsal view in an 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 re-expand 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 non-ionic 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 the thoracic duct and its tributary lymphatics; likely useful for surgical planning.

Pathologic Findings

  • Lymphatics (including the thoracic duct)-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 ⬆ ⬇

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 an 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”).

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 the 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 thoracic duct 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

Thoracic Duct 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; a 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 thoracic duct ligation.
  • Salvage procedures for recurrence after thoracic duct ligation include cisterna chyli and thoracic duct glue embolization, pleuroperitoneal or pleurovenous shunts or placement of a PleuralPort.

Medications ⬆ ⬇

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 µg/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 ⬆ ⬇

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 ⬆

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

  • CT = computed tomography
  • EDTA = ethylene diamine tetra-acetate
  • FIP = feline infectious peritonitis
  • TD = thoracic duct

Suggested Reading

Allman DA, Radlinsky MG, Ralph AG, Rawlings CA. Thoracoscopic thoracic duct ligation and thoracoscopic pericardiectomy for treatment of chylothorax in dogs. Vet Surg 2010, 39 (1):21–27.

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.

Johnson EG, Wisner ER, Kyles A, Koehler C, Marks SL. Computed tomographic lymphography of the thoracic duct by mesenteric lymph node injection. Vet Surg 2009, 38(3):361–367.

Author Jill S. Pomrantz

Consulting Editor Lynelle R. Johnson

Acknowledgment The author and editors acknowledge the prior contribution of Theresa Fossum.

Client Education Handout Available Online