Malignant Pleural Effusion - An Overview

Introduction

The pleura is a membrane that lines the lungs and the thoracic cavity and reduces friction between them. An abnormal fluid collection in the pleural cavity (a thin space between the parietal and visceral pleura) is known as pleural effusion. It can occur due to inflammatory disorders, pneumonia, lung cancer, and other conditions. Pleural effusion compresses the lungs, reducing their ability to expand completely during breathing, resulting in chest pain, cough, and shortness of breath. Malignant pleural effusion is an advanced form of the condition wherein the malignant cells from lung cancer or metastatic diseases spread into the pleural space causing pleural effusion. It is a frequent complication of malignancy and a serious disorder that significantly affects the quality of life of patients. Malignant pleural effusion requires a team of healthcare specialists to manage it, along with supportive care.

What Is Malignant Pleural Effusion?

Malignant pleural effusion (MPE) is the fluid accumulation between the lung and the chest wall due to cancerous cells in the pleura. Effusions usually indicate advanced malignancy and ipsilateral pleural involvement is seen in most cases with lung cancer. The cancer cells increase the production of pleural fluid and also reduce absorption. The majority of MPE in males is caused by lung cancer and in females by metastasis of breast cancer. The majority of cases of MPE are associated with pleural mesothelioma, a rare tumor of the pleura. Every year, the United States and Europe report around 500,000 new cases of MPE. Most malignant pleural effusions associated with breast cancer have a poor prognosis and are caused by lymphatic spread. Bilateral pleural effusions are observed in approximately 55 percent of patients who are critically ill and in about 15 percent of individuals who are noncritically ill.

What Causes Malignant Pleural Effusion?

Malignant pleural effusion occurs when cancerous cells from either lung cancer or any other type of cancer spread to the pleural space. However, the development of this condition MPE depends on several factors, such as:

• Anatomical factors such as reduction in pleural fluid resorption can cause excess fluid buildup in the pleural cavity.

• Overproduction of pleural fluid can also be caused by molecular factors such as chemical mediators, including tumor necrosis factor (TNF) and inflammatory cytokines, which increase vascular permeability. Gene mutations of MET, RET, BRAF, EGFR, and KRAS can also contribute to the development of MPE. Reduced partial pressure of oxygen in the blood can also cause pleural fluid accumulation, which can activate mechanoreceptors and alter lung volumes, leading to dyspnea or breathing difficulties.

What Are the Symptoms of Malignant Pleural Effusion?

Symptoms of malignant pleural effusion vary among patients as it may be asymptomatic in some and extremely bothersome in others. The tumor cells invade the pleura by direct infiltration from neighboring structures or via lymphatic spread or bloodstream and float in pleural fluid or adhere to the mesothelium by tumor seeding. These cancerous cells invade the immune system, acquire nutrients and growth factors, and cause symptoms such as:

• Fever.

• Cough.

• Fatigue.

• Dyspnea (difficulty breathing).

• Reduced physical activity.

• Clubbing.

• Muscle weakness.

• Chest pain and discomfort.

• Pain during deep breathing.

How Is Malignant Pleural Effusion Diagnosed?

A combination of clinical evaluation, laboratory analysis, and imaging studies is used to diagnose malignant pleural effusion. Depending on the signs and symptoms of the patient, the doctor may recommend one or more radiological examinations and laboratory tests. Imaging studies are vital in MPE as they help to evaluate and assess the extent of pleural involvement and fluid buildup, guide thoracentesis (removal of excess fluid), detect underlying malignancies and monitor treatment response. These include:

• Chest X-ray: It is the first line of investigation in the diagnosis of MPE. A minimum of 200 mL (milliliter) of fluid must be present in the pleural cavity to be detected in a posteroanterior view. The presence of severe effusion, loss of lung volume, and loculation may suggest MPE.

• Ultrasound: It is one of the best methods to view the pleural space, and guide to drain the pleural fluid. It detects smaller amounts of fluid, does not involve any radiation, and also differentiates between an effusion, thickened pleura, and consolidation.

• Computed Tomography (CT Scan) of the Chest: It provides a better view and gives more detailed information about the condition. Contrast-enhanced CT scan is considered the gold standard for suspected patients with pleural malignancy.

• Magnetic Resonance Imaging (MRI): It gives a better soft tissue resolution than computed tomography and is more sensitive in diagnosing chest wall and diaphragm.

• Diagnostic Thoracentesis: It is a standard test performed by removing a small amount of pleural fluid and analyzing for the presence of pleural fluid protein, pH, glucose, cytology, and microbiology. Approximately 40 to 60 cc of pleural fluid is necessary for diagnosing MPE.

• Plural Biopsy: It includes removing a small tissue of pleura from the chest cavity and examining for any malignant condition. It can be done using a needle or by surgery and is performed in patients whose cytology results are negative.

• Pleural Fluid Analysis: It is the testing of the pleural fluid sample using one or more laboratory techniques to determine the cause of pleural effusion. Pleural fluid tumor marker levels are mainly used to confirm the diagnosis of malignant pleural effusion.

• Thoracoscopy: It is an invasive procedure performed if thoracentesis is not effective or if more tissue is required for detecting molecular markers. It is a technique in which a camera is inserted into the thoracic cavity to visualize the pleura, drain the pleural fluid, and also take samples for biopsy to analyze the condition.

How Is Malignant Pleural Effusion Managed?

MPE is managed by a team of expert medical professionals, including pulmonologists, oncologists, and radiologists. The primary goal is to treat the underlying malignancy with immunotherapy, radiation, or chemotherapy and prevent fluid accumulation. Several other treatments are available to remove the pleural fluid or to avoid reaccumulation and enhance breathing. These include:

• Thoracentesis: It is performed using a needle or a catheter, which is inserted into the pleural cavity to drain the excess fluid. It helps confirm MPE but further fluid build-up or continuous drainage may not be possible.

• Pleurodesis: In this method, a chemical or a sclerosing agent is instilled into the thoracic cavity after draining the excess pleural fluid to obliterate the space between the parietal and visceral pleura. As a result, the pleural surfaces become sticky and adhere together, thus minimizing the risk of fluid build-up.

• Indwelling Pleural Catheter: It is a small catheter inserted under the skin and into the pleural fluid to allow repeated drainage which helps relieve the symptoms of MPE. It is placed under local anesthesia and is completely safe and easy to use. It also facilitates lung expansion and promotes breathing. The catheter is removed once the patient’s condition improves or fluid-up resolves.

Conclusion

Malignant pleural effusion occurs when fluid accumulates in the pleural cavity due to the presence of malignant cells. Dyspnea is one of the most common symptoms of this condition, which substantially affects the patient’s quality of life. It is diagnosed by various imaging tests and histopathological examinations along with clinical assessment. The treatment of malignant pleural effusion is challenging and may also be associated with certain complications. However, an interprofessional approach using advanced medical care, periodic monitoring, and timely interventions can benefit the patients in managing this condition.