Final answer:
Superior vena cava syndrome affecting only one side of the body is potentially due to an obstruction in one of the brachiocephalic veins, which form the superior vena cava, responsible for returning blood from the upper body to the heart.
Step-by-step explanation:
The superior vena cava is a large systemic vein that returns blood to the heart from the superior portion of the body, including the head, neck, chest, shoulders, and upper limbs. In the event of superior vena cava syndrome that affects only one side of the body, it's possible that only one of the brachiocephalic veins, which merge to form the superior vena cava, is involved. The systemic circuit involves blood flow to and from virtually all of the body tissues. The superior vena cava handles the return of this blood from the upper body. Superior vena cava syndrome typically restricts blood flow, causing symptoms in the areas drained by the involved veins. Factors contributing to such unilateral superior vena cava syndrome could include a localized mass or thrombosis in one of the brachiocephalic veins.