A 68-year-old man presents to the emergency room with a two-week history of severe cough and shortness of breath, worse when lying flat or bending over. He reports associated headaches, dizziness, lightheadedness, hoarseness of voice, and dysphagia. He has a 20-year history of smoking (one pack per day) and works as an electrician. Vital signs: Temperature: 99 °F Heart rate: 98 beats/min Respiratory rate: 34 breaths/min Blood pressure: 145/95 mm Hg Physical Examination: Swelling of the tongue, face, neck, and upper extremities. Dilated neck veins and collateral veins over the anterior chest wall. Positive Pemberton’s sign (reddish facial tinge with arm elevation). Imaging: Chest X-ray reveals unilateral widening of the superior mediastinum on the right side. Which of the following tests helps to confirm the diagnosis in this patient?
