<prompt> The commonest cause of pulmonary embolism is -Thrombosis of leg veinsThrombosis of prostatic veinsIVC thrombosisThrombosis of internal pudendal artery  <response>: Thrombi in a deep vein of the leg accounts for more than 95 of cases of pulmonary embolism.The most common source of emboli is DVT of femoropopliteal and iliac veins.But remember that :Most common site of DVT is calf veinsCalf veins thrombosis are itself associated with a low risk for embolism, but when the thrombosis progresses proximally to involve the larger veins above knee, then the risk becomes very high. 