Malignant Mesothelioma of the Pleura
Section snippets
HISTORICAL BACKGROUND
One of the first clues leading to the eventual link between asbestos and mesothelioma was the observation that tumors occurred more frequently in coastal cities than elsewhere.3 Subsequently, investigations in South African coal miners confirmed that exposure to asbestos was associated with an increased incidence of mesothelioma.4 This observation, made in 1960, has been confirmed in numerous studies.5, 6, 7 Although malignant mesothelioma probably was initially described before 1900,8 it was
EPIDEMIOLOGIC FEATURES
Approximately two-thirds of the patients with diffuse malignant pleural mesothelioma are between the ages of 50 and 70 years.12 Rarely, the tumor occurs in children.13 The incidence of malignant mesothelioma is 2 to 6 times higher in men than in women. Wives of men employed in asbestos-related work also have an increased incidence of mesothelioma.14
The incidence of malignant mesothelioma in populations considered minimally exposed to asbestos was estimated at one case per million per year in
CLINICAL FEATURES
The gradual onset of chest pain is the most common (60%) initial manifestation in most series of patients with diffuse malignant mesothelioma.32, 38, 39 This pain is typically nonpleuritic. Dyspnea is the next most frequent respiratory complaint (40%). Fever, chills, sweats, or weakness and malaise have been reported in a considerable number of patients. Cough is relatively uncommon (10%). A small percentage of patients have an acute onset of severe pain and dyspnea, usually related to either
RADIOLOGIC FINDINGS
The most common chest x-ray finding in patients with malignant mesothelioma is a unilateral pleural effusion; the incidence varies from 30 to 95%.32, 38, 39, 40, 41, 42 A mediastinal shift toward the affected side, even in the presence of a large amount of fluid, should suggest the possible presence of mesothelioma. Most reported series describe a small number of patients with mesothelioma who have bilateral pleural effusions; thus, this finding should not be used as evidence against the
LABORATORY DATA
Serum chemistries, hemoglobin concentration, and leukocyte counts are typically normal at the time of diagnosis of malignant mesothelioma. Thrombocytosis (more than 400,000 platelets/mm3) was noted in 90% of patients in one series.27 The erythrocyte sedimentation rate can exceed 100 mm in 1 hour.
Laboratory features of pleural fluid obtained from patients with mesothelioma have been well described,5, 12, 27 but they are not diagnostic. Half the effusions are bloody. Most are exudates with a
DIAGNOSIS
Among patients with mesothelioma, a needle biopsy specimen of the pleura is usually insufficient to make the diagnosis. Because of its small size, it was considered diagnostic in only 25% of cases in one series12 and 39% in another.46 Needle biopsy often fails to provide enough tissue to enable the pathologist to exclude reactive mesothelial proliferations confidently. In addition, needle biopsy does not permit gross inspection and palpation of the pleura, both of which may be helpful in
PATHOLOGIC FEATURES
Localized fibrous mesotheliomas (so-called benign mesotheliomas) are probably mesenchymal tumors derived from submesothelial mesenchymal cells rather than tumors of the mesothelial lining cells.11, 49 They are single masses9, 10, 11, 49 (rarely multiple) usually attached by a pedicle to the visceral pleura. Histologically, they are composed of spindle cells with intervening dense collagen, and most of these lesions are histologically benign, lacking mitotic figures and cellular anaplasia.
DIFFERENTIAL DIAGNOSIS
Several entities can cause considerable diagnostic confusion and therefore warrant discussion of their distinguishing features: localized fibrous mesothelioma, benign asbestos-related effusion, rounded atelectasis, and metastatic adenocarcinoma. A summary of the various clinical, radiologic, and pathologic findings in these and other conditions is shown in (Table 4).
Localized fibrous mesothelioma has a tendency to occur more often in women than in men (2:1), is not associated with exposure to
NATURAL HISTORY
Early in its course, malignant mesothelioma may primarily cause recurrent pleural effusions that necessitate repeated therapeutic thoracenteses. As the tumor expands and enlarges, eventually encasing a substantial amount of the surface area of the lung, effusions become less of a management problem. Dyspnea becomes a factor as tumor encasement begins to restrict lung expansion. Local spread to ribs and intercostal nerves is a late occurrence and may precipitate intractable chest wall pain.
THERAPY
Therapy for malignant mesothelioma has included three modalities used individually or in combination: operation, irradiation, and chemotherapy. The extent of surgical treatment is based on preoperative goals. Surgical attempts to remove all tumor usually entails pleuropneumonectomy and, occasionally, excision of the ipsilateral hemidiaphragm and pericardium. Palliative surgical intervention, most commonly pleurectomy, is aimed at preventing recurrent effusions and decreasing pain from chest
CONCLUSION
Malignant mesothelioma of the pleura is increasing in incidence in the United States and is beginning to be seen more often in persons without clear-cut occupational exposure to asbestos. The clinical features of dyspnea and chest pain accompanied by pleural thickening with or without effusion have been well described. The pathologic diagnosis usually necessitates acquisition of a generous specimen; thus, open pleural biopsy is necessary in most cases. Unfortunately, this procedure may be
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