They may result from a variety of pathological processes which overwhelm the pleura's ability to reabsorb fluid. The lack of specificity is mainly due to the limitations of the imaging modality. Given that most effusions are detected by x-ray, which generally cannot distinguish between fluid types, the fluid in question maybe simple transudative fluid, blood, pus, chylous fluid, etc. If simple fluid, then the term hydrothorax may be employed, although this is rarely used other than in combination terms e. If additional corroborative evidence is available, certain mostly non-transudative effusions are preferentially designated using more specific terminology. This is important because these effusions may be managed distinctly.
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They may result from a variety of pathological processes which overwhelm the pleura's ability to reabsorb fluid. The lack of specificity is mainly due to the limitations of the imaging modality. Given that most effusions are detected by x-ray, which generally cannot distinguish between fluid types, the fluid in question maybe simple transudative fluid, blood, pus, chylous fluid, etc. If simple fluid, then the term hydrothorax may be employed, although this is rarely used other than in combination terms e.
If additional corroborative evidence is available, certain mostly non-transudative effusions are preferentially designated using more specific terminology. This is important because these effusions may be managed distinctly. These are discussed separately:. As the accumulation of fluid in the pleural space occurs in a broad range of disparate clinical scenarios, no single demographic is affected; rather the epidemiology will match that of the underlying condition.
However, it is probably safe to say that as congestive cardiac failure and malignancy are some of the most common causes, older patients would be over-represented. A small amount of fluid is completely asymptomatic. In fact, depending on the respiratory reserve of the patient, even large amounts of fluid can accumulate within the pleural space before any symptoms are recognized.
Physiologically, the pleural cavities normally contain approximately 15 mL of serous fluid 6. Any process which results in more fluid forming than can be absorbed will produce a pleural effusion. There are many causes of pleural effusion that are broadly split into transudates and exudates.
This categorization relies upon the biochemical analysis of aspirated pleural fluid 5 :. It occurs due to the increase in permeability of the microcirculation or alteration in the pleural space drainage to lymph nodes. It occurs when there is an increase in hydrostatic pressure or a decrease of capillary oncotic pressure. They are usually found in the context of gas or blood in the pleural cavity, and do not exclude a malignant cause.
Chest radiographs are the most commonly used examination to assess for the presence of a pleural effusion; however, it should be noted that on a routine erect chest x-ray as much as mL of fluid is required before it becomes evident 6.
A lateral decubitus projection is most sensitive, able to identify even a small amount of fluid. At the other extreme, supine projections can mask large quantities of fluid. A lateral decubitus film obtained with the patient lying on their side, effusion side down, with a cross table shoot through technique can visualize small amounts of fluid layering against the dependent parietal pleura.
Lateral films are able to identify a smaller amount of fluid as the costophrenic angles are deepest posteriorly. A subpulmonic effusion a. It can be difficult to identify on frontal radiographs. They are more common on the right, and usually unilateral. The following features are helpful 6 :. Large amounts of fluid can be present on supine films with minimal imaging changes, as the fluid is dependent and collects posteriorly.
There is no meniscus, and only a veil-like increased density of the hemithorax may be visible. It is therefore especially difficult to identify similar sized bilateral effusions as the density of the lungs will be similar. Ultrasound allows the detection of small amounts of pleural locular fluid, with positive identification of amounts as small as mL, that cannot be identified by radiographs, which is only capable of detecting volumes above 50 mL of liquid.
Contrary to the radiological method, ultrasound allows an easy differentiation of loculated pleural fluid and thickened pleura.
Moreover, it is effective in guiding thoracentesis thoracocentesis , even in small fluid collections 4. When viewed in a coronal plane, with the ultrasound transducer at the mid to posterior axillary line, the space above the hemidiaphragm is typically occupied by an artifactual reflection of hepatic or splenic architecture, with inspiratory obscuration of the projected location of the posterior costophrenic sulcus as the lung descends.
The spine is also obscured as it extends into the thorax. One may observe how, with the collection of fluid superior to the hemidiaphragm 13 :. Homogeneously anechoic effusions may be either transudates or exudates, but any degree of heterogeneity is pathognomonic of a complex effusion non-transudative. Exudative effusions often demonstrate punctate, hyperechoic foci floating within the effusion, referred to as the plankton sign.
Septations may be seen in the pleural fluid, and may indicate underlying infection but can be seen in chylothorax or hemothorax 8. The appearance of the " hematocrit sign " may be observed in hemothorax, with a surface layer of anechoic fluid sitting atop a settled, fine echogenic sediment.
Ultrasound can be used in the assessment of pleural effusion volume. Refer to the article " Pleural effusion volume ultrasound " for more information. CT scanning is excellent at detecting small amounts of fluid and is also often able to identify the underlying intrathoracic causes e. CT is not able to differentiate between a transudative or exudative pleural effusion with similar fluid densities and non-differentiating rates of loculation and pleural thickening 9, However, CT can help distinguish between a pleural effusion and a pleural empyema see pleural effusion vs pleural empyema.
The treatment of pleural effusions is usually targeted to the underlying condition e. Symptomatic patients with large effusions may be treated by therapeutic aspiration thoracentesis. When effusions are very large, this can safely be done 'blind' although increasingly ultrasound is used to at least mark an appropriate site.
Ultrasound-guided aspiration is reliable and fast and enables loculated effusions to be drained. A catheter can be left in situ, although care must be taken to ensure that it is connected either to an underwater drain or to a sealed system such that air cannot enter the pleural cavity.
If effusions reaccumulate despite repeated aspirations and systemic therapy where appropriate , a tunnelled semipermanent pleural drain or video-assisted thoracic surgery VATS pleurodesis can be considered. Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys.
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Article information. System: Chest. Section: Gamuts. Tag: pleura. Synonyms or Alternate Spellings: Hydrothoraces Hydrothorax Differential of a pleural effusion Differential diagnosis of a pleural effusion Differential diagnosis for a pleural effusion Pleural effusions. Support Radiopaedia and see fewer ads. Cases and figures. Figure 1 Figure 1. Case 1: from fluid overload Case 1: from fluid overload.
Figure 2: meniscus photo Figure 2: meniscus photo. Case 2: on ultrasound Case 2: on ultrasound. Case 3: pleural metastases Case 3: pleural metastases. Case 4: subpulmonic effusion Case 4: subpulmonic effusion. Case 5: pleural effusion Case 5: pleural effusion.
Case 6: meniscus well illustrated Case 6: meniscus well illustrated. Case 7: the thoracic spine sign Case 7: the thoracic spine sign. Case 8: on right Case 8: on right. Case 9 Case 9. Case 10 Case Case loculated Case loculated. Case massive with midline shift Case massive with midline shift.
Case supine pleural effusion Case supine pleural effusion. Imaging differential diagnosis. Inferior pulmonary ligament Inferior pulmonary ligament. Phrenic nerve palsy Phrenic nerve palsy. Lower lobar collapse and consolidation Lower lobar collapse and consolidation.
Pleural effusion is the abnormal accumulation of fluid in the pleural space the area between the two layers of the thin membrane that covers the lungs. Fluid can accumulate in the pleural space as a result of a large number of disorders, including infections, tumors, injuries, heart, kidney, or liver failure, blood clots in the lung blood vessels pulmonary emboli , and drugs. Symptoms may include difficulty breathing and chest pain particularly when breathing and coughing. Diagnosis is by chest x-rays, laboratory testing of the fluid, and often computed tomography angiography. See also Overview of Pleural and Mediastinal Disorders. Normally, only a thin layer of fluid separates the two layers of the pleura.
A pleural effusion is excess fluid that accumulates in the pleural cavity , the fluid-filled space that surrounds the lungs. This excess fluid can impair breathing by limiting the expansion of the lungs. Various kinds of pleural effusion, depending on the nature of the fluid and what caused its entry into the pleural space, are hydrothorax serous fluid , hemothorax blood , urinothorax urine , chylothorax chyle , or pyothorax pus commonly known as pleural empyema. In contrast, a pneumothorax is the accumulation of air in the pleural space, and is commonly called a "collapsed lung". The most common causes of transudative pleural effusion in the United States are heart failure and cirrhosis. Nephrotic syndrome , leading to the loss of large amounts of albumin in urine and resultant low albumin levels in the blood and reduced colloid osmotic pressure, is another less common cause of pleural effusion. Pulmonary emboli were once thought to cause transudative effusions, but have been recently shown to be exudative.
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