Pleural tumors can be categorized into primary and secondary types, with the latter referring to metastasis of tumors from other sites to the pleura. Virtually any primary malignancy can metastasize to the pleura, with breast cancer and lung cancer being the most common primary tumors. Patients with pleural metastases may be asymptomatic or may present with symptoms such as chest tightness, shortness of breath, or respiratory difficulty due to pleural effusion. Diagnosis of pleural metastases may be achieved through cytological analysis of pleural fluid obtained by thoracentesis or pleural biopsy via thoracoscopy. Treatment primarily focuses on addressing the primary tumor. For patients with significant pleural effusion causing respiratory distress, thoracentesis or closed drainage may help relieve compression of lung tissue. Intrathoracic administration of drugs or biological agents may be employed to reduce pleural fluid exudation.
Primary pleural tumors are relatively rare. For example, the incidence rate of pleural mesothelioma ranges between 0.02% and 0.4%. Primary tumors originating from the subpleural connective tissues are even less common and include tumors of smooth muscle, blood vessels, lymphatic vessels, nerves, and adipose tissue, each of which may present as either benign or malignant tumors.
Pleural mesothelioma is a rare tumor derived from mesodermal tissue, with the majority being malignant. Its occurrence is closely associated with prolonged asbestos exposure. Clinically, pleural mesotheliomas are classified into two types: diffuse and localized.
Diffuse Malignant Pleural Mesothelioma
This type represents a primary pleural tumor originating from mesothelial cells, characterized by high malignancy, extensive disease involvement, and, in some cases, rapid progression and poor prognosis. Diffuse malignant pleural mesothelioma can occur at any age but is most commonly diagnosed between the ages of 40 and 70, with a higher prevalence among men. Symptoms are often nonspecific at the onset and may include dyspnea, persistent severe chest pain, and dry cough. Hemorrhagic pleural effusion is frequently observed, and minor hemoptysis may occur if the tumor invades the lung or bronchi. Rare clinical findings include ipsilateral Horner's syndrome or superior vena cava obstruction syndrome. Advanced stages may lead to anorexia, weight loss, and systemic decline. Chest CT scans are useful in assessing the extent of the disease and the involvement of intrathoracic organs. Diagnosis may be aided by cytological analysis of pleural fluid, percutaneous pleural biopsy, thoracoscopic pleural biopsy, or thoracotomy with pleural biopsy. Treatment for diffuse pleural mesothelioma remains challenging. Extrapleural pneumonectomy is rarely performed due to its high morbidity, significant complications, and uncertain survival benefits. Recent advancements in pharmacological treatments have led to some therapeutic progress.
Localized Pleural Mesothelioma
This type tends to grow slowly and is clinically more common than diffuse malignant mesothelioma. Most cases are benign, with approximately 50% of patients remaining asymptomatic. Symptomatic cases may present with cough, chest pain, or fever, occasionally accompanied by pleural effusion. Chest CT scans often reveal localized pleural masses or nodular elevations. Localized fibrous mesotheliomas are typically treated through surgical resection, with relatively favorable outcomes.