Elusive Unilateral Pleural Effusion: Keys to Clinching the Diagnosis

Unilateral pleural effusions may sometimes be difficult to diagnose. The cause may vary widely, including congestive heart failure, chronic liver and kidney disease, various drugs, and underlying undiagnosed disorders of the lung and pleura. With advancements in chest imaging, new biomarkers, and less invasive methods for obtaining tissue samples, it may be possible to identify the cause of the unilateral pleural effusions whose etiology is unclear. Even reviewing patient history, re-examining pleural fluid, classifying effusions based on Light's criteria, and ruling out pseudoexudates can help understand the cause. We aim to discuss a case of unilateral pleural effusion and, on its backdrop, discuss an approach to elusive unilateral pleural effusion.