Congestive Heart Failure (CHF): While CHF typically causes bilateral pleural effusions, it can occasionally present unilaterally, especially if there is underlying pulmonary or pleural disease. The effusion is usually transudative.

Pneumonia: Bacterial, viral, or fungal pneumonia can cause a unilateral pleural effusion, especially if the infection is severe or complicated by a parapneumonic effusion.
Pulmonary Embolism (PE): A large PE can cause a unilateral pleural effusion, often with associated chest pain and shortness of breath.
Lung Cancer: Malignant pleural effusions can be unilateral and are a common complication of lung cancer.
Pulmonary Tuberculosis: TB can cause a unilateral pleural effusion, often with associated fever, night sweats, and weight loss.

Empyema: A collection of pus in the pleural space, which can be life-threatening if not promptly treated with antibiotics and drainage.
Traumatic Hemothorax: A collection of blood in the pleural space, which can be life-threatening if not promptly treated with drainage and possible surgery.
Esophageal Rupture: A rare but potentially life-threatening condition that can cause a unilateral pleural effusion, often with associated chest pain and vomiting.

Chylothorax: A rare condition where lymphatic fluid accumulates in the pleural space, often due to trauma, cancer, or lymphatic disorders.
Uremic Pleuritis: A rare condition where kidney failure causes inflammation of the pleura, leading to a unilateral pleural effusion.
Sarcoidosis: A rare autoimmune disorder that can cause a unilateral pleural effusion, often with associated lung nodules and skin lesions.
Asbestos-Related Pleural Disease: A rare condition where exposure to asbestos causes inflammation and fluid accumulation in the pleural space.