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Pleural Effusion (Etiology and Different Varieties)

Mar 01, 2023


Pleural effusion is a common clinical finding with many potential underlying causes. It refers to fluid accumulation in the pleural space between the lung and the chest wall. This condition can result from various underlying conditions, such as heart failure, pneumonia, cancer, tuberculosis, and kidney disease.

Knowledge of pleural effusion is essential for medical professionals as it can be a significant diagnostic and therapeutic challenge.

In this blog we’ll discuss the etiology and different varieties of pleural effusion is important medicine topic for NEET PG exam preparation.

ENT Residency


  • Normal amount of fluid in Pleural space: 5-15 ml
  • Pleural fluid secreted by: Parietal Pleura
  • Rate of synthesis of pleural fluid : 0.01 ml/kg/hr (Some of this secreted fluid is reabsorbed by lymphatics)
  • Minimal Amount of fluid present in pleural cavity for Clinical Detection 300ml.
  • IOC for Minimal Pleural Effusion: CT chest > USG chest
  • Minimal Amount of fluid that should be present to confirm pleural effusion on CXR in Upright position
  • CXR Upright : Lateral view > 100ml
  • CXR Upright : Frontal view > 200ml
  • CXR Upright : Frontal view (Amount of fluid needed for obliteration of Hemi-diaphragm: > 500 ml
  • Characteristic of Pleural effusion on CXR
    • Obliteration /Blunting of CP angle (CP Angle → Costophrenic Angle)
    • Meniscus sign


  • 2 types of PE
    • Transudative
    • Exudative


Hydrostatic Pressure will drive the fluid out of vascular space/capillaries while Oncotic pressure will drive the fluid back into Intravascular compartment

  • Any condition causing
  • Conditions causing in Hydrostatic Pressure
    • CHF (MC)
    • Constrictive Pericarditis
    • Valvular lesions
  • Conditions causing in Oncotic pressure
    • Oncotic Pressure α Blood Albumin
    • ↓ Blood Albumin (HypoAlbuminemia) → ↓ Oncotic Pressure

Important information 

  • Hypoalbuminemiais seen in conditions like
  • Cirrhosis
  • Nephrotic Syndrome
  • Protein Losing enteropathy
  • Transudative Pleural Effusion is always B/Las pressure is distributed equally to left & Right Side.
  • Leading cause of B/L Pleural effusion →Heart Failure
  • Exudative Pleural effusioncan be U/L or B/L

Exudative Variety

  • Causes of Exudative Pleural Effusion
    • Parapneumonic Effusion (Pleural Effusion + Pneumonia)
    • Malignancy
    • TB
    • Rheumatoid Effusion
    • Meigs Syndrome

Important information 

  • On Thoracocentesis
    • Fluid Clotson standing in Exudate variety 
    • Fluid is transparent like water and Never Clots in Case of Transudate variety 
  • Thoracocentesis
    • Thoracocentesis is always done USG guided
    • >1 cm distance b/w Pleural surface & lung border (i.e. 1 cm of Fluid separating Lung border from Pleural Surface) on CXR is an Indication of Doing Thoracocentesis
    • Preferred site of Thoracocentesis 7th ICS (Inter Costal Space) in Scapular line

Different Varieties Of Pleural Effusion

  1. Pleural Effusion related to Malignancy
  • Usually there is occurs Massive Pleural Effusion in Malignancy (peripherally located cancer)

Important information 

  • Leading cause of Malignant Pleural Effusion → Ca Lung (Adenocarcinoma)
  • Leading cause of Malignant Ascites → Ca Ovary
  • Symptoms → Pt. C/O TREPEPNEA Dyspnea of Patient is Increasing on lateral Decubitus position.
  • Management
    • Diagnostic Thoracocentesis
      • Send the fluid to laboratory to confirm the Exudative variety based on LIGHT’s Criteria
    • Check for
      • Pleural Fluid Protein
      • Pleural Fluid LDH
    • Ideally any 1 of 3 present is sufficient for Diagnosis of Exudative Pleural Effusion.
      • However, in about 25% of cases light’s criteria may misdiagnose Transudate as Exudate.
    • Therefore we also check
      • Pleural fluid Sugar < 60 mg%
      • Cytology: Microscopic examination : Cancer Cells + nt
      • Pleural effusion in these cases of Malignancies recurs a lot after Thoracocentesis. To prevent this, we inject a sclerosing agent in pleural space which causes obliteration of pleural cavity and the fluid doesn’t reaccumulate. This procedure is k/as Pleurodesis
  • Rx: After Removing the fluid from pleural space, give the following drugs:
    • Injection Doxycycline Into pleural space via chest tube: Leads to formation of Adhesions in various layers of pleura ultimately causing Pleurodesis
    • Procedure of choice for Mx of patients with Malignant pleural effusion Pleurodesis

Important information 

  • Orthopnea:  Breathlessness ↑ing in supine position
    • Seen in Acute CHF
  • Platypnea
    • ↑ in Breathlessness in sittingposition
    • Seen in
    • Atrial Myxoma
    • Hepato pulmonary syndrome
  1. Parapneumonic Effusion
  • If Diagnosed later or failed to Diagnose: Can lead to Empyema which then is managed by Chest tube insertion in 5th ICS in Mid Axillary line.
  1. Tubercular Pleural Effusion
  • Classified as Extra-pulmonary TB
  • Adenosine Deaminase Levels ↑ in Pleural fluid
  • IOC - Pleural Biopsy gene Xpert / CBNAAT (Not Pleural Fluid gene Xpert)
  1. Rheumatoid Pleural Effusion
  • Inflammatory nodules in Lungs, Heart
  • On Skin present in Extensor Distribution
  • Inflammatory nodules undergo Breakdown that results in development of Exudates
  • On Microscopic Examination
  • Cholesterol crystals +nt in Pleural Fluid

Important information 

Low pleural Fluid Sugar: Seen in

  • Infection
  • Malignancy
  • Rheumatic Arthritis associated Pleural Effusion
  1. Meigs syndrome
  • Associated with
    • Ovarian Tumors
    • Fibroma / Thecoma
  • Ascites
  • Rt. sided Pleural effusion

Important information 

  • LEFT SIDED PLEURAL EFFUSION: Usually Encountered after surgical aspects
    • Acute Pancreatitis (Involving Tail of Pancreas)
    • Sympathetic Pleural Effusion
    • Boerhaave Syndrome (Rupture of Esophagus)
    • Esophageal Malignancy
  • Hemorrhagic Pleural Effusion 
    • Has Hematocrit Value 0.5 times that of blood
    • Seen with TB / Ca lung / Mesothelioma / Trauma
  • Mesothelioma→ A/w Asbestosis
    • Pleural Plaque Calcification
    • Hemorrhagic Pleural Effusion

Normal Pleural Fluid has the following characteristics              

  • Clear Ultrafiltrate of plasma that originates from the Parietal pleura
  • A pH of 7.60-7.64
  • Protein content of less than 2% (1-2 g/dL)
  • Fewer than 1000 white blood cells (WBCs) per mm3.
  • Glucose content similar to that of plasma
  • Lactate dehydrogenase (LDH) less than 50% of plasma


  1. Loculated Pleural Fluid / Empyema 
  2. Pleural fluid PH < 7.20
  3. Pleural Fluid glucose < 3.3 mmol/L (< 60 mg / dl)
  4. + ve Gram stain or culture of pleural fluid
  5. Presence of Gross pus in the pleural Space

Characteristics Of Important Exudative Pleural Effusion

Etiology or Type ofEffusionGross appearanceWhite Blood Cell Count(cells/mcL)Red Blood Cell Count(cells/mcL)GlucoseComments
MalignancyTurbid  to bloody: occasionally serous1000 to<  100,000 M100 to several hundred thousandequal to serum levels: < 60 mg/dl. In 15 % of casesEosinophilia uncommon; positive result on cytologicexamination
Uncomplicated parapneumonicClear to turbid5000-25,000 P< 5000equal to serum levelsTube  thoracostomyunnecessary
Empyematurbid to purulent25,000- 100,000 P< 5000Less than Serum levels: often very lowdrainage necessary; putrid odor suggests anaerobicinfection
TuberculosisSerous to serosanguineous5000- 10,000M< 10,000Equal  to serum levels: occasionally< 60 mg/dL.protein > 4.0 g/dL (may exceed 5 g/dL); eosinophils cells (> 10%) or mesothelial cells (>5%) make diagnosis unlikely: see text for additionaldiagnostic tests
RheumatoidTurbid; greenish yellow1000-20,000 M or P< 1000< 40 mg/dlSecondary empyema common; high LD, low complement, high rheumatoid factor, cholesterolcrystal areCharacteristic
Pulmonary infarctionserous to grossly bloody1000-50,000 M or P100 to100,000equal to serum levelsvariable findings: no pathognomonicfeatures
Esophageal ruptureturbid to purulent red- brown< 5000 to50,000 P1000-10,000usually, lowhigh amylase level (salivary origin); pneumothorax in 25% cases; effusion usually on left side: pH< 6.0 strongly suggestsDiagnosis
PancreatitisTurbid to serosanguineous1000-50,000 P1000-10,000equal to serum levelsUsually  left- sided; highamylase level


A. Haemorrhagic pleural effusion 

B. Chylous pleural effusion

c. Transudative Pleural effusion

  • Chylous Thoracic duct obstruction leads to Chylothorax: This Pleural Fluid is Milky White Colored and has ↑ Triglycerides
    • Cause of Chylothorax → Damage to lymphatics by Conditions such as Filariasis

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