The workup of a pleural abnormality begins with a complete history and physical examination. A thorough review of systems should be taken including specific queries about local symptoms such as pain, dyspnea, or cough, as well as more systemic findings such as fevers, weight loss, or neurologic symptoms.
A complaint of chest pain should be explored further—is the pain pleuritic? Was there antecedent trauma? Does the pain radiate to the top of the shoulder or scapula or back? The sensation of pain by the afferent nerve fibers of the parietal pleura secondary to inflammation or infection may be observed with hemothorax, parapneumonic effusion, or empyema (i.e., purulent fluid in the pleural space). On the other hand, changes in intrapleural pressures and stretching of parietal pleural surfaces on the chest wall or diaphragm may account for sensations of discomfort in cases of pneumothorax. The time course of the pain also might yield insight into the pathologic process. For example, a history of retching followed by acute epigastric or substernal pain and then progression to left-sided chest pain would suggest an esophageal rupture with initial mediastinitis followed by contamination of the left chest.
Dyspnea may reflect a true decrement in the lung function if the pathologic process usurps a significant volume within the hemithorax. This can be seen in patients in whom fluid or solid volume prevents full lung expansion. The respiratory mechanics also can be disrupted, such as may occur in cases of pneumothorax, where there is an uncoupling of the mechanical forces of the chest wall and diaphragm from the lung, with a resulting diminution of lung volume caused by the lung's intrinsic elastic recoil. However, dyspnea also may result without a significant loss of lung function. The sensation of incomplete chest expansion that accompanies some pleural processes may lead to dyspnea in the absence of hypoxia or hypoventilation.
A history of cough should be elicited to determine the characteristics of the sputum produced: color, odor, viscosity, amount, and frequency. A period of coughing that is productive of purulent sputum, in conjunction with a fever and chest pain, followed later by a persistent dry cough, may be an indication that a chronic empyema cavity has formed (see Chapter 107). A history of hemoptysis, weight loss, and heavy tobacco use in a patient with a pleural effusion would be suspicious for a malignant effusion or pleural malignancy.
A comprehensive physical examination often, but not always, corroborates the suspicions raised by an abnormal history. Auscultation, percussion, palpation, and testing for tactile fremitus or egophony all represent important aspects of the respiratory examination. It is equally important to detect pathology in other systems because the pleural space may represent only one manifestation of many in a particular disease. For example, a patient complaining of shortness of breath with stair climbing also may relate a long-standing history of joint pain and swelling. On examination, in addition to a dullness to percussion that shifts to the dependent aspects of the chest when the patient is moved from the sitting to the decubitus positions, one also might observe the severely gnarled joints and ulnar deviation of rheumatoid arthritis.
In practice, few diagnoses are made solely by physical examination. Radiologic examination of the pleural space is accomplished with plain chest radiographs, ultrasound, CT scan, and MRI. Plain films are usually the initial investigation of benign conditions from any of the three categories described earlier (Fig. 126-5). The scant volume of pleural fluid present in the healthy state is not visible on chest x-ray, but a pleural effusion of 50 mL should be detectable on a lateral chest film, evidenced as blunting of the posterior costophrenic sinus. A 200-mL effusion is evidenced by blunting of the lateral sulcus.12 On anteroposterior (portable) films, often the meniscus of the pleural effusion is indistinct, and atelectatic or consolidated lung may contribute to the basilar opacification. An upright posteroanterior and lateral film is preferable because it should be technically superior, but even that technique still may not distinguish the fluid component of such a finding. In these cases, a lateral decubitus chest x-ray may be performed to assess the effusion, which should layer dependently if it is free flowing and not loculated.
A. Spontaneous pneumothorax in the right pleural space. Note the absence of lung markings in the right hemithorax. Inset shows a coned-down view of the pleural edge of the collapsed right lung (white arrows). B. Right-sided hemothorax. This example of fluid in the pleural space is notable for a meniscus at the costophrenic sulcus. C. Fibrothorax. The arrow points to an area of opacification that represents the thickest portion of the chronic empyema cavity. At operation, the full extent of the fibrothorax ranged from the upper third of the hemithorax to the hemidiaphragm, as suggested by the more bland opacity seen on this plain film.
A plain upright chest x-ray is also the mainstay of radiologic evaluation of pneumothorax. Small amounts of air in the pleural space may be detected by observing the visceral pleural line (Fig. 126-5, inset) or noting the absence of lung markings. In an otherwise normal pleural space, the first location of detectable pneumothorax is usually the apex. Thus, in most instances, an upright plain film is the appropriate study to order, although there is experimental evidence from cadaver studies that a lateral decubitus film may be even more sensitive.13,14 The progressive collapse of the lung with increasing pneumothorax will continue to shorten the radial distances between the visceral pleural surfaces of the pulmonary lobes and the hilum. In a supine patient, the distribution of air within the pleural space is altered, and the pneumothorax may be noted as the “deep sulcus sign,” where the lateral sulcus is sharper and more lucent on the affected side or as lucency over the right or left upper quadrants.15,16
Chest CT scanning increases the sensitivity of detection of solid, liquid, and gas within the pleural space. Fluid collections can be further characterized by measuring Hounsfield units to distinguish between simple effusions and hemothorax or evolving empyemas.17 CT scanning is also more sensitive for the detection of pneumothoraces.18,19 It is worth stating that tension pneumothorax is not a diagnosis that should be made with CT or chest x-ray, but rather clinical assessment. Distinguishing between exudative and transudative pleural effusions is not reliably accomplished with CT scanning alone.20 In terms of surgical planning, a chest CT scan can be extremely useful in planning video-assisted thoracic surgery (VATS) port sites or even thoracotomy to avoid lung adhesions and obtain optimal access to the intrapleural pathology.
MRI of the chest may be useful in the workup of malignant disease because it demonstrates tumor invasiveness and thus resectability. It has a sensitivity of up to 100% and a specificity of up to 93% in the detection of malignant disease during a workup of pleural masses.21 Its role in the workup of benign disease is less clear. Although it is not accurate in distinguishing between exudate and transudate, MRI can detect hemothorax reasonably well.22 In practice, however, it is unlikely to be a necessary adjunct to clinical evaluation.
Ultrasound is less sensitive than CT scanning for the detection of pleural fluid and pneumothorax,18,19,23 although it may have increased specificity for distinguishing pleural thickening from pleural fluid.24 Ultrasound is also a portable tool, which has implications in the rapid assessment of critically ill patients in the trauma or intensive care settings. Compared with plain radiography, ultrasound is more sensitive for detecting and quantifying pleural fluid.25,26 For reasons of safety and efficacy, it is now recommended that procedures for evaluation of pleural effusion (e.g., thoracentesis) be performed with ultrasound guidance.27
Thoracentesis represents the first invasive modality in the workup of a pleural effusion. It bears mentioning that thoracentesis typically is not necessary in patients with bilateral pleural effusions and clinical scenarios that point to transudative causes.28 In one analysis it was found that the clinical judgment of the physician was correct in predicting a transudative effusion in 16 of 16 cases and in 15 of 17 exudative effusions.29
The British Thoracic Society guidelines for workup of a unilateral pleural effusion are depicted in Figure 126-6. The first goal of pleural fluid analysis is to distinguish between exudative effusions (e.g., cloudy serum signifying disease of the pleura itself) and transudative effusions (e.g., clear serum but abnormally high concentration). The different diagnoses associated with each type of effusion are listed in Table 126-1. As recommended, the fluid is then sent in three separate tubes for pleural chemistries (e.g., lactate dehydrogenase [LDH], pH, and protein), microbiologic analysis (e.g., aerobic and anaerobic culture, Gram stain, fungal culture, and AFB stain and culture), as well as cytology. Light's criteria are used to determine whether the fluid is transudative or exudative (pleural:serum LDH >0.6, pleural:serum protein >0.5, or pleural LDH >two-thirds of upper normal serum value).29,30 Whereas other assays have been described to distinguish exudates from transudates, Light's criteria have been validated and in clinical practice remain a mainstay of the workup.31 It is important to remember that the data may not return as classic profiles of malignant or benign disease. Certain data will “trump” others. For example, the finding of malignant cells on cytology yields a definitive diagnosis of malignant pleural effusion regardless of the protein and LDH levels. Similarly, the finding of pleural food particles suggests viscus (esophageal) perforation, independent of other findings. Other specific analyses can be run on the fluid, depending on the clinical situation. For example, the presence of milky fluid, suggestive of chylous effusion, would prompt the addition of a triglyceride level to the fluid analysis. Amylase levels of the pleural fluid specimen may be determined in suspected cases of pancreatic disease, keeping in mind that malignancy, esophageal rupture, tuberculosis, abdominal trauma, uremia, and radiation pleuritis also have been found to be associated with increased levels of amylase.32
Table 126-1Etiologies of Pleural Effusion ||Download (.pdf) Table 126-1Etiologies of Pleural Effusion
|FREQUENCY ||TRANSUDATE ||EXUDATE |
|Very common ||Left ventricular failure |
|Less common ||Hypothyroidism |
|Lung infarction |
Benign asbestos effusion
Postmyocardial infarction syndrome
|Rare ||Constrictive pericarditis |
Superior vena cava syndrome
|Yellow nail syndrome |
In cases of exudative effusion, when the diagnosis is still suspect, a pleural biopsy is warranted.33 The preferred route at our institution is by means of VATS. This is done under general anesthesia, with single-lung ventilation on the nonaffected side. The exploration and biopsy usually can be accomplished through a single 12-mm port. It is important to bear in mind that the pleural tissue obtained should be sent for both pathologic and microbiologic analyses.
Flow diagram for workup of unilateral pleural effusion based on British Thoracic Society guidelines.