Diagnosis

Pleuritic disease is suggested by thoracic pain on inspiration. More than 200 to 300 mL of fluid in the pleural space may also be detected by physical examination. Decreased breath sounds with dullness to percussion could suggest pleural fluid or lung consolidation, but pleural effusion may be distinguished by the presence of decreased tactile and vocal fremitus. Often, there is a small (1-2 cm) zone at the top edge of the pleural effusion where traditional signs of consolidation may be heard, including egophony. A pleural rub may be heard in areas of inflammation but disappears when significant fluid cushions the movement of visceral pleura against parietal pleura. For pneumothorax, significant air must be present in the pleural space to detect hyperreso-nance, although breath sounds are often decreased on the affected side. In the 1% to 2% of cases producing tension pneumothorax, in which air is able to enter the space but not equilibrate with either extrathoracic or bronchial air pressures, the clinician may detect tracheal shift, cardiac shift, or decreased heart sounds.

Chest radiography reveals blunting of the costophrenic angles and visible fluid when about 200 mL of fluid has accumulated in the pleural space. Decubitus positioning of the patient can reveal as little as 10 mL of fluid on the dependent side on chest films. Thoracentesis may be done blindly if the fluid layers out to at least 1-cm thickness on decubi-tus radiograph. Otherwise, ultrasound-guided thoracentesis may be indicated.

Pneumothorax is also visible on chest x-ray film, especially when it exceeds 10% or more than 100 mL of air is present in the pleural space. On radiographs, 2.5 cm of air space between the thoracic wall and the lung is equivalent to a 30% pneumothorax. This is best visualized on upright PA and lateral films or occasionally on the nondependent side when patients are in the decubitus position. Other imaging studies (CT, MRI) can give more anatomic detail in patients with mass lesions or scarring. These studies are also somewhat more sensitive than radiography in detecting small amounts of air in pneumothorax.

Diagnostic thoracentesis can help determine the type of fluid and potential causes. Transudates are serous fluids often associated with inflammatory conditions. Transudative fluid is thin and mildly yellow or straw colored, through which one can read newsprint. More specific laboratory criteria for differentiating exudate from transudate include a pleural/ serum protein ratio greater than 0.5, pleural/serum lactate dehydrogenase (LDH) level greater than 0.6 (or measured pleural LDH >200 IU/dL), and pleural protein greater than 3 g/dL.

Exudates indicate the presence of white blood cells and often a response to infection such as pleural abscess or TB. Parapneumonic effusions may be inflammatory transu-dates initially or may progress to exudative fluid as WBCs and even the infectious organism itself spread to the pleural space. Infectious exudates are suggested by pH higher than 7.2, which can be an indication for chest tube drainage. More specifically, TB may be suggested by an exudative pleural effusion with elevated WBC count, more lymphocytes than granulocytes, and pleural glucose/serum glucose ratio less than 0.5. Hemorrhage into the pleural space is indicated by the gross or microscopic presence of red blood cells, although poor technique can result in a bloody tap that is not diagnostic. For mass lesions or scarring, pleural biopsy may be obtained (revealing granulomas or malignancy) either percutaneously with needle or surgically in an open biopsy.

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