This is a basic article for medical students and other non-radiologists
Pleural fluid describes fluid within the pleural space. Fluid may be simple fluid, pus, hemorrhage and therefore is a broad description that includes, but not synonymous with pleural effusion. Pus in the pleural space may become loculated and in some cases, may have solid elements.
On this page:
Reference article
This is a summary article; we do not have a more in-depth reference article.
Summary
-
pathophysiology
- fluid within the pleural space
- causes
- simple fluid: pleural effusion
- high protein: exudate, e.g. infection
- low protein: transudate, e.g. pulmonary edema
- pus
- hemorrhage
- simple fluid: pleural effusion
-
role of imaging
- is there a pleural effusion?
- a chest x-ray is first line test
- US and CT are more sensitive and specific but not always required
- are there other features that suggest a cause?
- air-space opacification in pneumonia or heart failure
- cardiomegaly in heart failure
- focal lung lesion or collapse in lung cancer
- is it complex (septations or loculations)?
- ultrasound is best, but CT may help
- is it infected (enhancement)?
- CT is best; ultrasound is less sensitive
- what is the best way to drain it?
- ultrasound is helpful - most drainage will be ultrasound-guided
- is there a pleural effusion?
- common pathology
Radiographic features
Chest radiograph
- unilateral opacification without volume loss or air bronchograms
- usually basal
-
blunting of the costophrenic angle
- this may be the only sign in smaller effusions
- if it can be seen on a
- frontal chest x-ray, it measures at least 300-500 mL
- lateral chest x-ray, about 200 mL
Ultrasound
- fluid is dark (hypoechoic) on ultrasound
- the underlying lung may be consolidated
- additional features:
- septations: parapneumonic effusion or early empyema
- loculation: established pleural infection
- thick turbid fluid with echogenic material: empyema
CT chest
- the volume required for detection is much smaller than CXR
- fluid on CT is an intermediate density: 0-30 HU
- the density may help to determine the type of fluid
- simple fluid will have a lower HU than blood
- the density may help to determine the type of fluid
- if IV contrast is given, evidence of pleural enhancement may point to an infective cause