Inflammatory and Fibrosing Pleural Processes

Clinical Features

Effusions can develop at any age and are associated with a multiplicity of diseases and treatments. Parapneumonic effusions are quite common and are found in up to 40% of patients with bacterial pneumonia. Symptoms may be related to the primary disease or the presence of the fluid and include cough, chest pain, sputum production, and varying degrees of shortness of breath. Chest radiographs enable diagnosis.

Pathologic Features

Grossly, a layer of gray or tan material typically coats the pleura. The histologic changes can be divided into exudative, fibrinous, and organizing stages. In the exudative stage, the pleural capillaries are dilated, and there are reactive changes with enlargement of mesothelial cells, which remain in a single layer; small deposits of fibrin can be found adherent to the pleura. The fibrinous stage is characterized by layered fibrin deposition, granulation tissue, and mesothelial reaction ( Fig. 34.1A ). The mesothelial cells may be cytologically atypical, but the atypia is confined to the area of the organizing effusion, and mesothelial cells are never found in the underlying adipose tissue. The organizing stage is characterized by progressive fibrosis and a chronic inflammatory cell infiltrate ( Fig. 34.1B ). The fibrous tissue is most dense adjacent to the chest wall.

Prognosis and Therapy

The course of the effusion depends on its etiology and the responsiveness of the underlying condition to therapy. Many effusions require drainage, and some will require surgical intervention. Diagnostic thoracentesis is appropriate in cases of significant parapneumonic effusions to differentiate infected, complicated effusions from uncomplicated effusions, with the former requiring tube thoracostomy. In effusions complicating other diseases, drainage is initiated on a case-by-case basis. Decortication is reserved for those patients who have inadequate drainage after tube thoracostomy and for those patients with persistent pleural thickening and significant pulmonary function deficits.

Clinical Features

Approximately 60% of empyemas develop from parapneumonic effusions. At the present time, anaerobic organisms are more commonly isolated than aerobic organisms, with most patients having more than one organism identified. Postsurgical (pneumonectomy) empyemas are an important clinical problem, and empyemas uncommonly follow thoracentesis. Empyema is infrequently found as a complication of pleural rheumatoid nodules, probably because of the formation of bronchopleural fistulas with necrosis of the nodules.

Symptoms (cough, sputum production) may be those of the adjacent pneumonic process, when empyema complicates a parapneumonic effusion. Other symptoms and signs include fever and leukocytosis, expectoration of pleural fluid (if a bronchopleural fistula is present), air–fluid levels in the pleural space, or drainage of purulent material from an incision or needle tract.

Pathologic Features

Grossly, the pleura is usually coated with a layer of tan or yellow-green material ( Fig. 34.2A ). Microscopically, empyemas progress through the same general stages as uncomplicated effusions, but the fibrinous stage is characterized by a thick layer of neutrophils ( Fig. 34.2B ). Chemical analysis of pleural fluid shows a low pH (less than 7.2) and a low glucose level (less than 30 mg/dL).

Prognosis and Therapy

Tube thoracostomy combined with antibiotic therapy represents the usual primary therapy; multiple tubes may be required if more than one locule is present. Decortication may be necessary if pleural sepsis is not controlled by the tube thoracostomies. Development of a bronchopleural fistula is an important complication; if the infected pleural fluid is not drained exteriorly, it is likely to drain interiorly and produce a severe bronchopneumonia.

Clinical Features

Eosinophilic pleuritis is classically induced by pneumothorax and is often seen in resected bullae. It can, however, also be found as a consequence of a pleural effusion or hemothorax, or in settings of infections with parasites (hydatid disease, amebiasis, ascariasis) or fungi. Occasionally, it may be associated with an adjacent eosinophilic pneumonia.

Pathologic Features

Numerous eosinophils infiltrate the pleura and are often accompanied by macrophages, giant cells, and other inflammatory cells ( Fig. 34.3 ). Reactive mesothelial cell proliferation may also be present.

Prognosis and Therapy

Infective eosinophilic pleuritis must be treated with antimicrobial agents and drainage. Simple reactive eosinophilic pleuritis due to pneumothorax has no consequence, whereas those cases secondary to hemothorax may require drainage or decortication.