Pleural Pathology Special Pathology

Pathologic involvement of the pleura; most often, a secondary complication of some underlying disease common pleural findings at autopsy Secondary infections and pleural adhesions Important primary disorders include; (1) primary intrapleural bacterial infections imply seeding of this space as an isolated focus in the course of a transient bacteremia (2) a primary neoplasm of the pleura: mesothelioma

Pleural effusion; common manifestation of both primary and secondary pleural diseases may be inflammatory or noninflammatory Normally, no more than 15 mL of serous, relatively acellular, clear fluid lubricates the pleural surface. Accumulation of pleural fluid occurs in the following settings:    Increased hydrostatic pressure, as in congestive heart failure    Increased vascular permeability, as in pneumonia       Decreased osmotic pressure, as in nephrotic syndrome      Increased intrapleural negative pressure, as in atelectasis    Decreased lymphatic drainage, as in mediastinal carcinomatosis

Inflammatory pleural effusions Serous, serofibrinous, and fibrinous pleuritis all are caused by essentially the same processes. Fibrinous exudations generally reflect a later, more severe exudative reaction might have presented as a serous or serofibrinous exudate, in an earlier developmental phase Common causes of pleuritis are inflammatory diseases within the lungs; tuberculosis pneumonia lung infarcts lung abscess bronchiectasis

Serous or serofibrinous pleuritis Rheumatoid arthritis disseminated lupus erythematosus uremia diffuse systemic infections, other systemic disorders metastatic involvement of the pleura can also cause. Serofibrinous pleuritis Radiation therapy for tumors in the lung or mediastinum Mostly the serofibrinous reaction is only minimal fluid exudate is resorbed with either resolution or organization of the fibrinous component. Accumulation of large amounts of fluid can sufficiently encroach on lung space to cause respiratory distress

Empyema A purulent pleural exudate usually results from bacterial or mycotic seeding of the pleural space Mostly seeding occurs by contiguous spread of organisms from intrapulmonary infection, but Occasionally occurs through lymphatic or hematogenous dissemination from a more distant source Rarely, infections below the diaphragm, subdiaphragmatic or liver abscess, may extend by continuity through the diaphragm into the pleural spaces, more often on the right side.

Empyema characterized by loculated, yellow-green, creamy pus composed of masses of neutrophils admixed with other leukocytes may accumulate in large volumes (up to 500 to 1000 mL), usually the volume is small, and the pus becomes localized Empyema may resolve, but this outcome is less common Organization of the exudate, with the formation of dense, tough fibrous adhesions frequently obliterate the pleural space or envelop the lungs; either can seriously restrict pulmonary expansion

True hemorrhagic pleuritis manifested by sanguineous inflammatory exudates is infrequent Found in hemorrhagic diatheses, rickettsial diseases, and neoplastic involvement of the pleural cavity The sanguineous exudate must be differentiated from hemothorax When hemorrhagic pleuritis is encountered, careful search should be made for the presence of exfoliated tumor cells

Hydrothorax Noninflammatory collections of serous fluid within the pleural cavities The fluid is clear and straw colored may be unilateral or bilateral, depending on the underlying cause most common cause; cardiac failure, usually accompanied by pulmonary congestion and edema. Transudates may collect in any other systemic disease associated with generalized edema found in renal failure and cirrhosis of the liver.

Hemothorax Chylothorax escape of blood into the pleural cavity almost invariably a fatal complication of a ruptured aortic aneurysm or vascular trauma may occur post-operatively. Pure hemothorax is readily identifiable by the large clots that accompany the fluid component of the blood Chylothorax accumulation of milky fluid, usually of lymphatic origin, in the pleural cavity. Chyle is milky white because it contains finely emulsified fats most often caused by; thoracic duct trauma obstruction that secondarily causes rupture of major lymphatic ducts malignant conditions within the thoracic cavity that cause obstruction of the major lymphatic ducts. More distant cancers may metastasize via the lymphatics and grow within the right lymphatic or thoracic duct to produce obstruction.

Pneumothorax air or gas in the pleural cavities may be spontaneous, traumatic, or therapeutic Spontaneous pneumothorax may complicate any form of pulmonary disease that causes rupture of an alveolus An abscess cavity that communicates either directly with the pleural space or with the lung interstitial tissue may also lead to the escape of air. In the latter circumstance the air may dissect through the lung substance or back through the mediastinum (interstitial emphysema), eventually entering the pleural cavity Pneumothorax is most commonly associated with; emphysema, asthma, tuberculosis Traumatic pneumothorax usually caused by some perforating injury to the chest wall, but sometimes the trauma pierces the lung and thus provides two avenues for the accumulation of air within the pleural spaces Resorption of the pleural space air occurs slowly in spontaneous and traumatic pneumothorax, provided that the original communication seals itself

One that attracts greatest clinical attention is spontaneous idiopathic pneumothorax encountered in relatively young people, seems to be due to rupture of small, peripheral, usually apical subpleural blebs, and usually subsides spontaneously as the air is resorbed. Recurrent attacks are common and can be quite disabling.

When the defect acts as a flap valve Pneumothorax may have as much clinical significance as a fluid collection in the lungs also causes compression, collapse, and atelectasis of the lung may be responsible for marked respiratory distress Occasionally the lung collapse is marked When the defect acts as a flap valve permits the entrance of air during inspiration but fails to permit its escape during expiration, it effectively acts as a pump that creates the progressively increasing pressures of tension pneumothorax, which may be sufficient to compress the vital mediastinal structures and the contralateral lung

Pleural tumors Pleura may be involved by primary or secondary tumors Primary pleural tumors Solitary (Localized) Fibrous Tumors Malignant mesotheliomas Secondary pleural tumors primary neoplasms of the lung and breast Any organ of body

Secondary metastatic involvement far more common than are primary tumors most frequent metastatic malignancies arise from primary neoplasms of the lung and breast malignancy from any organ of the body may spread to the pleural spaces. Ovarian carcinomas, for example, tend to cause widespread implants in both the abdominal and thoracic cavities In most metastatic involvements, a serous or serosanguineous effusion follows that often contains neoplastic cells For this reason, careful cytologic examination of the sediment is of considerable diagnostic value

Solitary (Localized) Fibrous Tumors Previously called "benign mesothelioma" or "benign fibrous mesothelioma" in the pleura and "fibroma" in the lung, localized fibrous tumors are now recognized as soft tissue tumors with a propensity to occur in the pleura and, less commonly, in the lung, as well as other sites. often attached to the pleural surface by a pedicle may be small (1 to 2 cm in diameter) or may reach an enormous size, but it tends to remain confined to the surface of the lung do not usually produce a pleural effusion.

Solitary (Localized) Fibrous Tumors Grossly, they consist of dense fibrous tissue with occasional cysts filled with viscid fluid; microscopically, the tumors show whorls of reticulin and collagen fibers among which are interspersed spindle cells resembling fibroblasts. Rarely, these tumors may be malignant, with pleomorphism, mitotic activity, necrosis, and large size (>10 cm). The tumor cells are CD34+ and keratin-negative by immunostaining This feature can be diagnostically useful in distinguishing these lesions from malignant mesotheliomas ( which show the opposite phenotype The solitary fibrous tumor has no relationship to asbestos exposure.

Malignant mesotheliomas in the thorax arise from either the visceral or the parietal pleura Although uncommon, they have assumed great importance in the past few years because of their increased incidence among people with heavy exposure to asbestos In coastal areas with shipping industries in the United States and Great Britain and in Canadian and South African mining areas, up to 90% of reported mesotheliomas are asbestos-related. The lifetime risk of developing mesothelioma in heavily exposed individuals is as high as 7% to 10%. There is a long latent period of 25 to 45 years for the development of asbestos-related mesothelioma, and there seems to be no increased risk of mesothelioma in asbestos workers who smoke. This is in contrast to the risk of asbestos-related lung carcinoma, already high, markedly magnified by smoking. Thus, for asbestos workers (particularly those who are also smokers), the risk of dying of lung carcinoma far exceeds that of developing mesothelioma.

Clinical Course presenting complaints are; chest pain, dyspnea, and, recurrent pleural effusions. Concurrent pulmonary asbestosis (fibrosis) is present in only 20% of patients with pleural mesothelioma The lung is invaded directly, and there is often metastatic spread to the hilar lymph nodes and, eventually, to the liver and other distant organs. Fifty per cent of patients die within 12 months of diagnosis few survive longer than 2 years. Aggressive therapy appears to improve this poor prognosis in some patients extrapleural pneumonectomy, chemotherapy, radiation therapy

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