Unilateral Pleural Effusion as The Initial Manifestation of Occult Lung Carcinoma: A Case Report

Pleural effusion is a common clinical condition with a wide differential diagnosis, ranging from benign inflammatory processes to advanced malignancy. In some patients, malignant pleural effusion may represent the first manifestation of an underlying lung cancer. Early recognition and systematic evaluation are therefore essential for timely diagnosis and management. We report the case of a fifty eight year old Saudi male who presented with progressive shortness of breath and right sided chest discomfort of three weeks duration. The patient had a long history of cigarette smoking but no previous diagnosis of malignancy. Physical examination revealed reduced chest expansion and markedly diminished breath sounds over the right lower lung zone. Initial chest radiography demonstrated a moderate right sided pleural effusion without a clearly visible lung mass. Further diagnostic evaluation included contrast enhanced computed tomography of the chest, which confirmed a large right sided pleural effusion with partial lung collapse, mild pleural thickening, and a small irregular lesion in the right upper lobe. Diagnostic thoracentesis yielded exudative pleural fluid according to Light criteria. Microbiological studies were negative for bacterial infection and tuberculosis. Cytological examination of the pleural fluid revealed atypical epithelial cells suspicious for malignancy, and repeat analysis supported the diagnosis of malignant pleural effusion. Subsequent CT guided biopsy of the right upper lobe lesion demonstrated histopathological features consistent with pulmonary adenocarcinoma. Management initially focused on symptomatic relief through pleural fluid drainage and supportive care. Following confirmation of the diagnosis, the patient was referred for oncologic evaluation and further staging. This case highlights the importance of considering malignancy in patients presenting with unexplained pleural effusion, particularly in individuals with significant smoking history, and emphasizes the role of pleural fluid analysis and tissue biopsy in establishing the diagnosis.