Diseases of the Pleura and Pleural Space

By Charbel on Jul 6, 2011 | In Health, Pulmonary Diseases

Diseases of the Pleura and Pleural Space

Steven A. Sahn

S.A. Sahn: Division of Pulmonary and Critical Care Medicine, Medical University of South Carolina, Charleston, South Carolina 29425.

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Pleural Effusions

Transudates

Exudates
Pneumothorax

Classification

Primary Spontaneous Pneumothorax

Secondary Spontaneous Pneumothorax
Bibliography

PLEURAL EFFUSIONS
The clinical recognition of a pleural effusion signifies that an abnormal physiological state exists whereby there is a dysequilibrium between the formation and removal of pleural fluid. The pleural fluid usually is the sequela of primary pulmonary disease but can also result from disease in an extrapulmonic focus such as the heart (congestive heart failure), kidneys (nephrotic syndrome), liver (cirrhosis), and pancreas (acute pancreatitis). Pleural fluid can also result from systemic diseases, such as systemic lupus erythematosus, metastatic malignancy, and iatrogenic causes such as drug therapy (nitrofurantoin) and extravascular migration of central venous catheters. Thus, patients with pleural effusions may present not only to the pulmonologist but to the internist, family physician, medical specialist, and surgeon.
The clinical presentation, chest radiographic findings, pleural fluid analysis, treatment, and outcome of the most common causes of transudates and exudates are discussed (see Chapter 12).
Transudates
Congestive Heart Failure
Congestive heart failure is the most common cause of a transudative effusion and probably is the most common cause of all pleural effusions, certainly in those over the age of 60 years. The precise incidence of pleural effusion with congestive heart failure is difficult to ascertain, as there is variance in the study populations, the techniques of detecting the effusions, and the stage and degree of heart failure at the time of evaluation. Clinically, about 40% of patients with congestive heart failure have pleural effusions; however, if a more sensitive technique such as ultrasonography is used to evaluate such patients, the incidence would be substantially higher. Pleural effusions in the presence of congestive heart failure are related to elevated pulmonary venous pressures, and most patients with congestive heart failure effusions have pulmonary capillary wedge pressures ³24 mmHg. Interestingly, this is the pulmonary venous pressure associated with visualization of Kerley B-lines on a chest radiograph. It appears that pleural effusions result when high pulmonary venous pressures cause increased filtration of fluid from the microvessels into the lung interstitium, and this interstitial fluid moves along a pressure gradient between mesothelial cells into the pleural space.
If pleural fluid formation exceeds pleural space lymphatic drainage, then fluid will accumulate in the pleural space. Patients with an isolated increase in right atrial pressures or patients with primary pulmonary hypertension do not develop pleural effusions, thus supporting the association of elevated pulmonary venous pressures and the development of pleural effusions. For example, patients with COPD and cor pulmonale rarely have pleural effusions. Patients with pleural effusions from congestive heart failure always have left ventricular failure and frequently associated right ventricular failure.
Most patients with pleural effusions secondary to congestive heart failure have the classic symptoms and signs. The chest radiograph shows cardiomegaly and bilateral small to moderate-size pleural effusions of relatively equal size, with the right being slightly greater than the left. There is usually evidence of pulmonary congestion on chest radiograph, and the severity of pulmonary edema appears to correlate with the presence of pleural effusions.
The pleural fluid is a transudate with mesothelial cells and lymphocytes accounting for the majority of the cells; it is unusual for the neutrophil count to exceed 10%. Acute diuresis over several days can transform the congestive heart failure transudate into a pseudoexudate.
In the patient with clinical congestive heart failure, bilateral pleural effusions, and an enlarged cardiac silhouette, finding a transudative effusion makes a presumptive diagnosis. Treatment consists of decreasing pulmonary venous hypertension and improving cardiac output with diuretics, digitalis, and afterload reduction. When heart failure is managed successfully, the effusions resolve over days to weeks. In patients with refractory heart failure and symptomatic pleural effusions, unilateral chemical pleurodesis should be considered.
Hepatic Hydrothorax
Pleural effusions occur in approximately 6% of patients with cirrhosis of the liver and clinical ascites. However, in rare cases, hepatic hydrothorax can occur without clinical ascites. Pleural fluid results from movement of ascitic fluid through diaphragmatic defects. When enough ascitic fluid is present, peritoneal pressure exceeds pleural pressure, and fluid moves through the diaphragmatic defects into the pleural space.
The patient usually has the physical stigmata of cirrhosis and clinically apparent ascites. With a large to massive pleural effusion, the patient may present with acute dyspnea, but with a smaller effusion, dyspnea may be present only with exertion, or the effusion may be detected on a routine chest radiograph.
The typical chest radiograph shows a normal cardiac silhouette and a right-sided pleural effusion (70%) that can vary from small to massive (<10%); effusions are sometimes isolated to the left pleural space (15%) or are bilateral (15%). Thoracentesis shows a serous transudate with a low nucleated cell count and a predominance of mononuclear cells, a pH > 7.40, a glucose similar to that in serum, and a low amylase concentration. Fluid can be hemorrhagic in the presence of an underlying coagulopathy.
A transudative right pleural effusion in the setting of cirrhosis with ascites provides a presumptive diagnosis. To be more certain, the clinician can compare pleural and ascitic fluid protein and LDH values, which should be similar. On occasion, the protein and LDH may be slightly higher in the pleural fluid than in ascitic fluid; this occurs when the increased portal pressure prevents reabsorption of non-protein-containing fluid by the peritoneum. To absolutely confirm the diagnosis, injection of a radiolabeled tracer into the ascitic fluid with detection on chest imaging within 1 to 2 hrs supports pleural–peritoneal communication through a diaphragmatic defect. Spontaneous bacterial empyema has been noted and occurs by hematogenous seeding or transfer of infected ascites through a diaphragmatic defect.
The treatment of hepatic hydrothorax is directed at the ascites with sodium restriction and diuresis. A pleural effusion frequently persists unchanged until all the ascites have been mobilized clinically. Patients refractory to therapy who remain symptomatic from a large pleural effusion can best be treated by thoracoscopy with repair of the diaphragmatic defect and pleural abrasion/talc pondrase. These patients should not undergo chest tube drainage because it can lead to hypovolemia, protein depletion, and immunosuppression. Patients with spontaneous bacterial empyema usually can be treated with antibiotics without chest tube drainage.
Nephrotic Syndrome
Pleural effusions are frequent in nephrotic syndrome (21% in one series), with the incidence varying with the degree of hypoalbuminemia. The mechanism responsible for pleural fluid accumulation is decreased oncotic pressure in the pleural microvascular circulation as a result of hypoalbuminemia; increased hydrostatic pressure from salt and water overload may also be contributory.
Patients with pleural effusions from nephrotic syndrome usually have anasarca by the time pleural effusions develop. In the evaluation of a pleural effusion in a patient with nephrotic syndrome, pulmonary thromboembolism needs to be considered, as this complication occurs in approximately a third of patients. The chest radiograph in patients with nephrotic syndrome usually shows small to moderate bilateral pleural effusions without evidence of pulmonary edema.
Thoracentesis reveals a serous transudate with a small number of mononuclear cells, a normal glucose concentration, and a pH > 7.40. The presence of hemorrhagic fluid, an increased protein concentration, or neutrophil predominance suggests thromboembolic disease or another diagnosis. Treatment should be directed at arresting the protein-losing nephropathy. A therapeutic thoracentesis should be done only for increasing dyspnea. If medical therapy is ineffective for the symptomatic pleural effusion, chemical pleurodesis should be considered.
Hypoalbuminemia from any cause is associated with bilateral pleural effusions. When the albumin concentration is £1.8 g/dl, pleural effusions may develop. It is unusual for patients with hypoalbuminemia to have edema fluid isolated only to the pleural space, as the pleural lymphatics are effective in clearance of a moderate amount of increased pleural fluid formation. Therefore, by the time patients with hypoalbuminemia develop pleural effusions, they have anasarca. Other causes of hypoalbuminemia that result in pleural effusions include severe malnutrition, which is commonly seen in patients admitted to the ICU and in end-stage AIDS, and in patients with protein-losing enteropathy.
Atelectasis
Atelectasis is a common cause of small pleural effusions in the postoperative patient, especially following upper abdominal surgery, and in patients in medical intensive care units. Atelectasis was the cause of pleural effusions in 23% of patients admitted to a medical intensive care unit. Atelectatic effusions also occur with major bronchial occlusion from lung cancer, a mucus plug, or foreign body. The mechanism producing atelectatic effusions is decreased pleural pressure. With alveolar collapse, the lung and chest wall separate further, creating local areas of increased negative pressure. This decrease in pleural pressure favors the movement of fluid into the pleural space, presumably from the parietal pleural surface. Fluid accumulates until the parietal pleural interstitium/pleural space pressure gradient returns to normal. The chest radiograph typically shows small unilateral or bilateral pleural effusions with normal heart size and absence of parenchymal infiltrates. Pleural fluid in acute atelectasis has not been studied in detail; however, in patients with mainstem bronchial obstruction and a chronic effusion, the fluid is a serous transudate with a small number of mononuclear cells, a normal glucose concentration, and a pH > 7.40. It is not known whether effusions from atelectasis remain transudates or transform into exudates over time. If the stoma remain patent and there is no preferential removal of liquid over protein, the fluid should remain a transudate. The diagnosis is presumptive in the proper clinical setting. Treatment should be directed at reversing the cause of the atelectasis. If it is successful, the pleural effusion resolves over several days.
Peritoneal Dialysis
Although peritoneal dialysis frequently is associated with small, transient pleural effusions, massive right pleural effusions are occasionally seen. These large effusions usually occur within 48 hr after the initiation of peritoneal dialysis and presumably result from opening of a congenital diaphragmatic defect from the increased peritoneal pressure, causing a rapid transfer of fluid from the peritoneal to the pleural cavity. Patients generally present with the acute onset of dyspnea. The chest radiograph shows a large to massive right pleural effusion with contralateral mediastinal shift. Thoracentesis shows pleural fluid resembling the dialysate. The total protein is usually <1 g/dl with a nucleated cell count of <100/ml and a glucose concentration in the 300 to 400 mg/dl range. The combination of a protein concentration <1 g/dl and a markedly elevated glucose concentration virtually confirms the diagnosis. Rapid movement of a radiolabeled tracer from the peritoneal to the pleural cavity confirms the diaphragmatic defect if there is doubt about the diagnosis. Continued drainage from the peritoneal catheter should be allowed to occur and will result in pleural space drainage as well. If the patient has severe dyspnea or cardiovascular instability, a therapeutic thoracentesis should be performed promptly. The most effective long-term treatment is to change to hemodialysis. The effusion will resolve completely with discontinuation of peritoneal dialysis, but success also has been reported after switching from continuous ambulatory peritoneal dialysis to intermittent dialysis in the semierect position.
Urinothorax
Urinothorax, a pleural effusion secondary to obstructive uropathy, has been associated with carcinoma of the genitourinary system, nephrolithiasis, trauma, surgical stent manipulation, and following renal transplantation. With urinary tract obstruction and hydronephrosis, perirenal and retroperitoneal fluid collections can occur. Pleural fluid moves from the retroperitoneal space through diaphragmatic defects into the pleural space. Patients present with evidence of urinary tract obstruction; the pleural effusion is suspected because of acute dyspnea or is discovered on a routine chest radiograph. The pleural effusion is always ipsilateral to the obstructed kidney; the chest radiograph shows a small to moderate pleural effusion without other abnormalities. Thoracentesis shows a straw-colored transudate with the odor of urine. The nucleated cell count is low, with a predominance of mononuclear cells. Pleural fluid glucose is similar to blood glucose; pleural fluid pH has been reported from 7.00 to 8.00. The pleural fluid pH depends on the urinary pH and on how rapidly the fluid moves from the perirenal area into the pleural space. The pH of a urinothorax is probably determined by the rate of hydrogen ion back-diffusion into the blood from extravasated acidic urine during passage from the retroperitoneal to the pleural space. As the hydrogen ion gradient is dissipated during the movement of fluid, the fluid pH approaches blood pH. Thus, the pH of urinothorax should lie intermediate between that of urine and blood, generally acidic, but can be alkaline if the urine pH is high. Urinothorax is the only cause of pleural fluid acidosis in the setting of a transudative effusion.
The diagnosis of urinothorax can be established by finding a pleural fluid/serum creatinine ratio >1.0. Early thoracentesis may be an important factor for diagnostic sensitivity, as the longer the fluid remains in the pleural space, the more likely equilibration between pleural fluid and serum will occur. In a patient with urinary tract obstruction, a low-pH transudate with a pleural fluid/serum creatinine ratio >1.0 establishes the diagnosis of urinothorax. Relief of the urinary tract obstruction results in prompt resolution of the effusion.
Trapped Lung
A trapped lung is the result of pleural inflammation that causes a pleural peel to develop over a portion of the lung surface. It is most commonly observed after empyema but can be seen with rheumatoid pleurisy, uremic pleuritis, benign asbestos pleural effusion (BAPE), malignancy and any other inflammatory pleural process. The trapped lung cannot expand to the chest wall, creating increased negative pleural pressure and increasing the parietal pleura/pleural space pressure gradient, leading to increased formation of pleural fluid. The formation of pleural fluid continues until a new steady state is reached. The patient may be asymptomatic if the effusion is small or complain of dyspnea if the area of trapped lung is large. The chest radiograph generally will show a small to moderate unilateral pleural effusion without other chest radiographic abnormalities. Thoracentesis usually shows fluid that is borderline between a transudate and exudate and has a small number of mononuclear cells with a normal pH and glucose. Diagnosis can be confirmed by finding a pleural liquid pressure of more negative than –7 cm H2O at the initial entry of the needle into the pleural space and a rapid decrement in pleural liquid pressure when a small volume of fluid is removed. Therapeutic thoracentesis usually results in rapid reaccumulation of a similar volume of pleural fluid. In the asymptomatic patient with a small effusion, no treatment is indicated; if the patient has a large symptomatic effusion, decortication is the treatment of choice. Decortication can be done years after the initial event with an excellent result as long as the underlying lung parenchyma is normal.
Constrictive Pericarditis
It is common knowledge that pleural effusions are associated with constrictive pericarditis, but it is not generally appreciated that a pleural effusion may be the presenting manifestation of constrictive pericarditis. Pleural effusion was the presenting feature in 60% of patients in one series of 30 patients, with some presenting as a pleural effusion of unknown origin. The most common cause of constrictive pericarditis today is cardiac surgery. Other causes include uremia, radiation therapy, tuberculous pericarditis, bacterial pericarditis, connective tissue diseases, malignancy, or fibrosing mediastinitis.
Constrictive pericarditis is an uncommon disorder with a varied presentation. It is misdiagnosed frequently as chronic liver disease, abdominal carcinomatosis, malignant pleural effusions, tuberculous pleurisy, and restrictive cardiomyopathy. The presenting symptoms include exertional dyspnea, peripheral edema, and increased abdominal girth. Jugular venous distention is the cardinal physical finding, with pleural effusions occurring in 50% to 60% of cases. Pedal edema and ascites are commonly present. The pleural effusions are caused by a combination of pulmonary and systemic venous hypertension, low oncotic pressure, and possibly inflammatory pericardial disease. The chest radiograph is abnormal in most patients, with the majority showing nonspecific findings such as pleural effusion and increased cardiac silhouette. Pericardial calcification, if present, is a specific finding in association with a typical presentation. The pleural fluid is serous and may be an exudate or a transudate, with the total protein concentration being <4 g/dl. Nucleated cell count is modest, usually being <5000/ml with a lymphocyte predominance. The pleural fluid glucose is equal to the serum glucose, and the pH is >7.30. When the diagnosis is suspected clinically, it can be confirmed by echocardiography, CT scan, or cardiac catheterization. Treatment is pericardiectomy.