Imaging pleural effusion

chest radiograph
  • small subpulmonary effusions not seen
  • minimal fluid best detected in lateral decubitus radiograph
  • 200 to 500 ml fluid needed for blunting of posterior and lateral costophrenic angles
  • homogenous opacification of lower chest
  • obliteration of costophrenic angle and hemidiaphragm
  • superior margin of opacity concave to lung and higher laterally than medially
  • above and medial to meniscus, hazy increase in opacity due to fluid posterior and anterior to lungs
  • 1000 ml of fluid when reaches 4th anterior rib
massive effusions
  • dense opacification of hemithorax with contralateral mediastinal shift
  • if mediastinal shift is absent in massive effusion – consider obstructive collapse of ipsilateral lung or extensive pleural malignancy like mesothelioma or metastatic carcinoma
  • large effusions can cause diaphragmatic inversion, usually left side due to lack of liver. can cause paradoxical diaphragm motion in affected side
subpulmonary effusion
  • < 200 ml of fluid localised under the lung.
  • presents as high hemidiaphragm with unusual contour that peaks more laterally than usual, has straight medial segment, and falls rapidly to costophrenic angle laterally.
  • separation of > 2 cm of stomach bubble from lung, particularly if displaced inferomedially
loculated / encysted / encapsulated effusion
  • between visceral pleural layers in fissures
  • between visceral and parietal pleural layers against chest wall
  • due to adhesions usually
  • transudates form without adhesions, usually within interlobar fissures, causing pseudotumors or vanishing tumors
  • differential: pleural mass. fluid is homogeneous, smooth when seen in tangent. poorly circumscribed when seen en face, changes configuration in supine and erect films. ultrasound helps identify fluid nature
supine patient
  • fluid layers posteriorly, no meniscus
  • veil like hazy opacity, with preserved vascular markings, no air bronchograms
  • apical cap that disappears on upright imaging
  • 175 ml only needed for apical cap
  • haziness of diaphragm margin
  • blunting of costophrenic angle
  • thickening of minor fissure
  • widening of paraspinal interface
  • transudate: echo free, marginated on deep aspect by bright line at fluid lung interface
  • exudates, hemorrhagic fluid: echogenic with pleural thickening . homogenous, complex or septated. change in form with position, mobile contents with respiratory movement favor fluid over a mass
  • key tool for distinguishing lung mass from fluid
  • fluid bronchograms and vessels favor consolidation
  • pleural lesions make obtuse angle with chest wall
  • intrapulmonary lesions make acute angle with chest wall
  • ultrasound confirms subpulmonary effusions
  • guided drainage of fluid and biopsy of masses
  • often reveals cause of effusion like subphrenic abscess or metastasis
computed tomography
  • distinguishes free and loculated fluid
  • identify extent and location
  • distinguish lung and pleural disease
  • distinguish empyema from lung abscess
  • characterize pleural thickening (benign or malignant)
  • identify thoracic or upper abdominal etiologies
  • dependent sickle shaped opacity of lower attenuation than pleura
  • does not distinguish transudate and exudate unless: parietal and visceral pleural thickening and enhancement (split pleura sign) suggests exudates due to malignancy or infection
  • loculated effusion has lenticular configuration
  • hemothorax shows high density due to clotted blood
  • chylothorax has high density due to protein content
  • limited role
  • helps distinguish transudate and exudate
  • effusion is T1 dark and T2 brighy
  • exudates are T2 brighter, with septations and nodules showing Gd enhancement
  • transudates have lower ADC
  • poor role in detecting pleural infection, best for identifying pleurocutaneous fistulae and osteomyelitis
  • superior contrast resolution helps to pick ups small nodules within the effusion
  • chylous effusion has high T1 similar to fat
  • bloody effusions show signals changes according to age of blood
  • increased glucose uptake by malignant cells, those responding to infection and inflammation
key points
  • left ventricular failure: usually bilateral large effusions, more on the right
  • post-cardiac injury syndrome: bilateral, associated consolidation and pericardial effusion
  • pulmonary embolism: small effusion, usually hemorrhagic
  • drugs: pleural thickening more than effusion. methotrexate, procarbazine, mitomycin, busulfan, bleomycin, interleukin-2, nitrofurantoin, ergotamine, methysergide, amiodarone, propylthiouracil, bromocriptine, gonadotrophins
  • pancreatitis: fluid rich in amylase
  • acute pancreatitis: exudative, blood stained, elevation of hemi diaphragm, basal lung consolidation
  • chronic pancreatitis: large, recurrent, patients present with dyspnea
  • sub-phrenic abscess: effusion with basal lung collapse and consolidation, elevated hemi diaphragm, subdiaphragmatic air-fluid level
  • uremia: exudative effusions, with pericarditis
  • peritoneal dialysis, cirrhosis: transdiaphragm passage of fluid. right sided, high glucose levels
  • obstructive uropathy: urinothorax
  • effusion in immune deficiency: due to pleural infections or NHL
  • suppurative exudate
  • parapneumonic
  • Three stages:
    1. exudative: >15000 WBC / ml
    2. fibrinopurulent: prominent adhesion formation
    3. organising: thick pleural peel
  • loculated effusion
  • split pleura sign
  • stranding, widening of extra pleural space
  • lung abscess: thicker more irregular wall, destruction of underlying lung
  • tuberculous: loculated with pleural calcification and enlargement of overlying ribs
  • disruption / obstruction of thoracic duct or collaterals
  • non traumatic: lymphoma
  • traumatic: most common surgical
  • right effusion: lower third thoracic duct injury
  • left effusion: upper two third duct injury
  • milky, contain triglycerides
  • associated with lymphangioleiomyomatosis