Final answer:
Superior Vena Cava Syndrome (SVCS) is caused by conditions that compress or obstruct the superior vena cava, with a mediastinal tumor being the most relevant cause out of the options listed.
Step-by-step explanation:
The syndrome caused by the superior vena cava is known as Superior Vena Cava Syndrome (SVCS). SVCS can be caused by any condition that compresses or obstructs the superior vena cava, leading to a range of symptoms due to impaired blood flow from the upper body back to the heart. While the options provided include pulmonary embolism, constrictive pericarditis, chest trauma, and a mediastinal tumor, the most closely related cause to SVCS among them is a mediastinal tumor. This is because a tumor in the mediastinum could compress the superior vena cava, leading to the obstruction of blood flow. Other potential causes of SVCS include thrombosis within the vein and external pressure from an enlarged thymus or swollen lymph nodes.