Recognizing a Pleural Effusion

Chapter 6 Recognizing a Pleural Effusion



Normal Anatomy and Physiology of the Pleural Space



image Normal anatomy
• The parietal pleura lines the inside of the thoracic cage and the visceral pleura adheres to the surface of the lung parenchyma, including its interface with the mediastinum and diaphragm (see Chapter 2, The Normal Frontal Chest Radiograph). The enfolds of the visceral pleura form the interlobar fissures—the major (oblique) and minor (horizontal) on the right, only the major on the left. The space between the visceral and parietal pleura, i.e., the pleural space, is a potential space normally containing only about 2-5 mL of pleural fluid.

image Normal physiology
• Normally, several hundred milliliters of pleural fluid are produced and reabsorbed each day. Fluid is produced primarily at the parietal pleura from the pulmonary capillary bed and is resorbed at the visceral pleura and by lymphatic drainage through the parietal pleura.


Causes of Pleural Effusions



image Fluid accumulates in the pleural space when the rate at which the fluid forms exceeds the rate by which it is cleared.
• The rate of formation may be increased by:
• Increasing hydrostatic pressure, as in left heart failure.

• Decreasing colloid osmotic pressure, as in hypoproteinemia.

• Increasing capillary permeability, as can occur in toxic disruption of the capillary membrane in pneumonia or hypersensitivity reactions.

• The rate of resorption can decrease by:
• Decreased absorption of fluid by lymphatics, either from lymphangitic blockade by tumor or from increased venous pressure, which decreases the rate of fluid transport via the thoracic duct.

• Decreased pressure in the pleural space, as in atelectasis of the lung due to bronchial obstruction.

image Pleural effusions can also form when there is transport of peritoneal fluid from the abdominal cavity through the diaphragm or via lymphatics from a subdiaphragmatic process (Table 6-1).

TABLE 6-1 SOME CAUSES OF PLEURAL EFFUSIONS

























Cause Examples
Excess formation of fluid Congestive heart failure
Hyponatremia
Parapneumonic effusions
Hypersensitivity reactions
Decreased resorption of fluid Lymphangitic blockade from tumor
Elevated central venous pressure
Decreased intrapleural pressure
Transport from peritoneal cavity Ascites


Types of Pleural Effusions



image Pleural effusions are divided into exudates or transudates, depending on their protein content and their lactate dehydrogenase (LDH) concentrations.

image Transudates tend to form when there is increased capillary hydrostatic pressure or decreased osmotic pressure, such as occurs in:
• Congestive heart failure, primarily left heart failure, which is the most common cause of a transudative pleural effusion

• Hypoalbuminemia

• Cirrhosis

• Nephrotic syndrome

image Exudates
• Most common cause of an exudative pleural effusion is malignancy.

• Empyema—an exudate containing pus

• Hemothorax—has a fluid hematocrit >50% blood hematocrit

• Chylothorax—contains increased triglycerides or cholesterol


Side Specificity of Pleural Effusions



image Certain diseases tend to produce pleural effusions on one side or the other, or bilaterally.

image Diseases that usually produce bilateral effusions:
• Congestive heart failure
• Usually about the same amount of fluid in each hemithorax.

• If markedly different amounts are in each hemithorax, suspect a parapneumonic effusion or malignancy on the side with the greater volume of fluid.

• Lupus erythematosus—usually bilateral, but when unilateral, the effusions are usually left-sided.

image Diseases that can produce effusions on either side (but are usually unilateral):
• Tuberculosis and other exudative effusions associated with infectious agents, including viruses

• Pulmonary thromboembolic disease

• Trauma

image Diseases that usually produce left-sided effusions:
• Pancreatitis

• Distal thoracic duct obstruction

• Dressler syndrome (Box 6-1, Fig. 6-1)

image Diseases that usually produce right-sided effusions:
• Abdominal disease related to the liver or ovaries—some ovarian tumors can be associated with a right pleural effusion and ascites (Meigs syndrome)

• Rheumatoid arthritis—the effusion can remain unchanged for years

• Proximal thoracic duct obstruction


Box 6-1 Dressler Syndrome



Postpericardiotomy/postmyocardial infarction syndrome

Typically occurs 2-3 weeks after a transmural myocardial infarct producing a left pleural effusion, pericardial effusion, and patchy airspace disease at the left lung base

Associated with chest pain and fever, it usually responds to high-dose aspirin or steroids

image

Figure 6-1 Dressler syndrome (postpericardiotomy/postmyocardial infarction syndrome).


A left pleural effusion (A) is present (solid black arrows). This syndrome typically occurs 2 to 3 weeks after a transmural myocardial infarct. It also can occur following pericardiotomy such as occurs in patients undergoing coronary artery bypass surgery, as in this case. The combination of chest pain and fever, left pleural effusion, patchy left lower lobe airspace disease, and pericardial effusion several weeks following a myocardial infarction or open-heart surgery should suggest the syndrome. It usually responds to high-dose aspirin or steroids. This patient has a dual lead pacemaker in place and, on the lateral projection (B), the leads are seen in the region of the right atrium (dotted black arrow) and right ventricle (arrowhead).



Recognizing the Different Appearances of Pleural Effusions



image Forces that influence the appearance of pleural fluid on a chest radiograph depend on the position of the patient, the force of gravity, the amount of fluid and the degree of elastic recoil of the lung.

image The descriptions that follow, unless otherwise indicated, assume the patient is in the upright position.


Subpulmonic Effusions



image It is believed that almost all pleural effusions first collect in a subpulmonic location beneath the lung between the parietal pleura lining the superior surface of the diaphragm and the visceral pleura under the lower lobe.

image If the effusion remains entirely subpulmonic in location, it can be difficult to detect on conventional radiographs except for contour alterations in what appears to be the hemidiaphragm but is actually the fluid-lung interface beneath the lung.

image The different appearances of subpulmonic effusions are summarized in Table 6-2 (Figs. 6-2 and 6-3).

TABLE 6-2 RECOGNIZING A SUBPULMONIC EFFUSION

image

image

Figure 6-2 Right-sided subpulmonic effusion.


In the frontal projection (A), the apparent right hemidiaphragm appears to be elevated (solid black arrow). This edge does not represent the actual right hemidiaphragm, which has been rendered invisible by the pleural fluid that has accumulated above it, but the interface between the effusion and the base of the lung (thus the term “apparent hemidiaphragm”). There is blunting of the right costophrenic sulcus (solid white arrow). On the lateral projection (B), there is blunting of the posterior costophrenic sulcus (solid white arrow). The apparent hemidiaphragm is rounded posteriorly but then changes its contour as the effusion interfaces with the major fissure on the left side (solid black arrow).


image

Figure 6-3 Left-sided subpulmonic effusion.


In the frontal projection (A), more than 1 cm distance is seen between the air in the stomach and the apparent left hemidiaphragm (double black arrow). The edge between the aerated lung and the dotted white arrow

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Mar 2, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Recognizing a Pleural Effusion

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