Though the information given is very limited but three factors, which have a bearing on the prognosis are known that the symptoms have been there for the last 5 months, the patient has been getting swelling of the legs and the fact that patient is 36 years old. I can conclude that the patient has Inferior vena cava thrombosis and almost certainly is due to the antiphospholipid syndrome or one of the thrombotic disorders like hypercysteinemia or other medical conditions, which predispose to the thrombosis.
The caval thrombosis is always a serious condition but it may not be life threatening all the time, more so if the condition has been there for the last 5 months then perhaps it has already passed through the dangerous period, that is when it can cause embolism and be life threatening. I still cannot minimise the seriousness of the condition so I suggest following line of action.
The investigations should be done urgently for the following:
1. To decide on the cause of the thrombosis. These investigations are both blood test and also general examination and x-rays and Ultra sound of the abdomen.
2. To decide on the level and size of the obstruction of the vena cava. (That is to decide if there is any lumen left in the cava and if the Renal vein is involved) The contrast-enhanced spiral CT is very helpful for this purpose. This will also focus on the collaterals which function as alternate conduit to the vena cava.
Once the investigations are sent for the patient should receive anticoagulant therapy if he is not already receiving the anticoagulants.
The results of the investigations should help in the decision of the further course of action. If the cause is antiphospholipid syndrome then he will need life long anticoagulant therapy. The intervention if needed and helpful (surgery or endovascular procedure should be left for few months or years and only undertaken if there is severe limitation). The cause could be some other disease, like tumour which will need to be addressed expeditiously.
Overall experience of the surgical treatment of vena cava thrombosis has not been very rewarding and has high morbidity and even mortality so medical therapy and other physical measures are mainstay and preferable.
One has also to remember that if the anticoagulant therapy is started then it will perhaps need to continue for life and should only be discontinued in consultation with the treating physician.