A 54-year-old construction worker has smoked two packs of cigarettes daily for the past 25 years. He notes swelling in his upper extremity and face, along with dilated veins in this region. A computerized tomography (CT) scan and venogram of the neck are performed. What is the most likely cause of the obstruction?

Bronchogenic carcinoma accounts for 70-80% of all cases of superior vena cava (SVC) obstruction; primary mediastinal tumors are the second most common cause. The main bronchial lymphatics are located at the tracheal bifurcation and immediately to the right and left of the trachea. Tuberculosis and mycotic infections are the most likely causes of chronic fibrosing mediastinitis.