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
ultrasound
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
mri
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
PET CT
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