Which of the following conditions could lead to bilateral edema?

Bilateral edema refers to swelling that occurs symmetrically in both legs. This condition can arise from systemic issues or problems in the veins that return blood to the heart. The presence of a thrombus, or blood clot, in the inferior vena cava can significantly impair venous return from the lower extremities. When blood flow is obstructed, it can lead to increased venous pressure, resulting in fluid leakage into the interstitial space and causing edema in both legs. This mechanism explains why a thrombus in the inferior vena cava is linked to bilateral edema.

The other conditions listed do not typically lead to bilateral edema. A femoral hernia might cause localized swelling, but it would not usually affect both legs symmetrically. Popliteal vein thrombosis primarily affects the affected leg due to obstruction in the local venous drainage. Varicose veins typically lead to localized swelling and discomfort in the affected limb, rather than bilateral swelling. Therefore, thrombus formation in the inferior vena cava is the most appropriate choice associated with bilateral edema.