Definition/General
Introduction:
Chylothorax is accumulation of lymphatic fluid (chyle) in pleural space
Contains high triglyceride levels (>110 mg/dL)
Results from thoracic duct injury or obstruction
Characterized by milky white appearance
Lymphocytic predominance in cellular composition.
Origin:
Results from thoracic duct disruption or obstruction
Traumatic causes: surgery, trauma (50% cases)
Non-traumatic causes: malignancy, congenital (50% cases)
Lymphatic malformations
Increased central venous pressure.
Classification:
Classified as traumatic vs non-traumatic
High-output (>1L/day) vs low-output (<1L/day)
Congenital vs acquired
Based on triglyceride levels: Chylous (>110 mg/dL), Pseudochylous (<110 mg/dL).
Epidemiology:
Rare condition: 1-2% of pleural effusions
Bimodal distribution: neonates and adults >50 years
Male predominance in traumatic causes
Equal gender distribution in non-traumatic causes
Right-sided more common (60% cases).
Clinical Features
Presentation:
Insidious onset of dyspnea
No fever or pleuritic pain
Gradually increasing pleural effusion
Weight loss and malnutrition
Fatigue and weakness
Immunodeficiency due to lymphocyte loss.
Symptoms:
Progressive dyspnea (90% cases)
Weight loss and malnutrition (60% cases)
Fatigue and weakness (50% cases)
Recurrent infections (30% cases)
Peripheral edema (25% cases)
Night sweats (20% cases).
Risk Factors:
Cardiac surgery (especially in children)
Esophageal surgery
Lung resection
Lymphoma (most common malignant cause)
Mediastinal tumors
Central venous cannulation
Birth trauma.
Screening:
Chest X-ray shows pleural effusion
CT thorax may show lymphadenopathy
Lymphangiography (rarely used)
Pleural fluid triglycerides >110 mg/dL
Chylomicron electrophoresis.
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Gross Description
Appearance:
Pleural fluid has characteristic milky white appearance
Creamy consistency
Odorless
Does not clear with centrifugation (unlike empyema)
Separates into cream layer on standing
May be blood-tinged if traumatic.
Characteristics:
Triglycerides >110 mg/dL (diagnostic)
Cholesterol <200 mg/dL
Protein 2.5-6 g/dL
Specific gravity 1.012-1.025
pH 7.4-7.8
Sudan III stain positive for fat globules.
Size Location:
Usually unilateral (80% cases)
Right-sided more common due to thoracic duct anatomy
May be bilateral in malignancy
Volume varies from small to massive
Rapidly reaccumulating after drainage.
Multifocality:
Predominantly right-sided (anatomy of thoracic duct)
Left-sided in upper thoracic duct injury
Bilateral in 20% cases (malignancy)
Free-flowing usually
Loculation uncommon.
Microscopic Description
Histological Features:
Pleural fluid shows lymphocytic predominance (>80%)
Small mature lymphocytes
Occasional large lymphocytes
Macrophages with lipid vacuoles
Lipid droplets in background
Low mesothelial cell count.
Cellular Characteristics:
Small lymphocytes with round nuclei and scant cytoplasm
Predominantly T-lymphocytes
Macrophages containing lipid vacuoles
Rare neutrophils
Few mesothelial cells
Fat globules visible with Sudan stain.
Architectural Patterns:
Dispersed lymphocytes
No clustering pattern
Lipid droplets scattered in background
Macrophages with foamy cytoplasm
Clear background with lipid material
No inflammatory debris.
Grading Criteria:
Diagnosis based on triglyceride levels >110 mg/dL
Lymphocyte count >80%
Cholesterol/triglyceride ratio <1.0
Chylomicron presence
Sudan III positive fat globules.
Immunohistochemistry
Positive Markers:
CD3 positive T-lymphocytes (predominant)
CD20 positive B-lymphocytes (fewer)
CD68 positive macrophages
Oil Red O positive lipid droplets (frozen sections)
Sudan III positive fat globules.
Negative Markers:
Cytokeratins (except rare mesothelial cells)
CEA, TTF-1 to exclude adenocarcinoma
CD15, CD30 to exclude lymphoma
S-100 to exclude melanoma
Calretinin in few mesothelial cells only.
Diagnostic Utility:
IHC rarely needed for chylothorax diagnosis
T-lymphocyte predominance supports diagnosis
Lipid stains demonstrate fat globules
Flow cytometry shows polyclonal T-cell population
Triglyceride level most important diagnostic test.
Molecular Subtypes:
T-helper cells (CD4+) predominant
T-cytotoxic cells (CD8+) present
Polyclonal T-cell population
Normal T-cell receptor rearrangement
No clonal lymphoid population.
Molecular/Genetic
Genetic Mutations:
No specific genetic mutations
Polyclonal lymphocyte population
Normal T-cell receptor genes
No immunoglobulin gene rearrangement
Reactive lymphocyte population.
Molecular Markers:
Triglycerides >110 mg/dL (diagnostic)
Cholesterol <200 mg/dL
Chylomicrons present
Apolipoprotein A-I elevated
Lipoprotein electrophoresis shows chylomicron band.
Prognostic Significance:
Etiology determines prognosis
Traumatic chylothorax: good prognosis with treatment
Malignant chylothorax: poor prognosis
Congenital cases: variable outcomes
Early treatment prevents complications.
Therapeutic Targets:
Conservative management: dietary modification (MCT diet)
Octreotide to reduce lymph flow
Pleurodesis for recurrent cases
Thoracic duct ligation for high-output cases
Treatment of underlying malignancy.
Differential Diagnosis
Similar Entities:
Pseudochylous effusion (cholesterol crystals)
Empyema (also milky but infectious)
Malignant pleural effusion (may be chylous)
Lymphoma with chylous effusion
Lipoid pneumonia with pleural involvement.
Distinguishing Features:
Chylothorax: Triglycerides >110 mg/dL
Chylothorax: Lymphocytic predominance
Pseudochylous: Cholesterol crystals
Empyema: Neutrophilic predominance
Malignant: Cytological atypia
Lipoid: Lipid-laden macrophages.
Diagnostic Challenges:
Distinguishing from pseudochylous effusion
Underlying malignancy may not be obvious
Traumatic vs non-traumatic etiology
Bilateral effusions may suggest malignancy
Need for triglyceride measurement.
Rare Variants:
Congenital chylothorax (neonates)
Post-surgical chylothorax
Malignant chylothorax (lymphoma)
Idiopathic chylothorax
Chylous ascites with chylothorax.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Pleural fluid, volume [X] mL, milky white, creamy consistency
Adequacy
Adequate for cytological and biochemical evaluation
Biochemical Analysis
Triglycerides: [X] mg/dL (>110 mg/dL diagnostic of chylothorax), Cholesterol: [X] mg/dL
Cellularity
Moderate cellularity with [X] cells/μL
Cell Differential
Lymphocytes: [X]% (>80%), Macrophages: [X]%, Mesothelial cells: [X]%, Neutrophils: [X]%
Morphological Features
Predominance of small mature lymphocytes. Macrophages with lipid vacuoles present. Background shows lipid droplets and clear fluid.
Special Stains
Sudan III stain: [Positive/Negative] for fat globules
Malignant Cells
No malignant cells identified
Final Diagnosis
Chylothorax (chylous pleural effusion)
Comment
Findings consistent with chylothorax based on elevated triglycerides and lymphocytic predominance. Recommend evaluation for underlying etiology including malignancy workup.