A 68-year-old woman with a 6-month history of progressive dyspnea and weight loss presents with a unilateral right-sided pleural effusion on chest X-ray. Thoracentesis shows an exudative fluid with positive cytology for adenocarcinoma. CT chest reveals a 3 cm mass in the right lower lobe with irregular borders, mediastinal lymphadenopathy, and a moderate right pleural effusion. The pleural fluid also shows elevated LDH (950 IU/L) and low pH (6.8). What is the most important imaging finding that would change the staging and treatment approach?