Thank you for choosing DoctorSpring.
I am sorry to hear about your illness.
Regarding the seriousness, yes this lesion is something to be concerned about. The lesion itself is large and so possibly it is compressing few brains structures nearby. The proximity to the Internal Carotid artery is another concern as this can make the removal of the tumor challenging.
On the positive side, you has symptoms for 3 years, so the lesion could have been there for 4 years or so. Such a long standing lesion means it is either non cancerous (benign) or a slow growing tumor. It can also be a cyst or growth from the sinus.
I would like to know whether you have any additional symptoms ? Such as weakness / numbness along arms or legs / loss of vision / hormonal imbalances / urinary symptoms .
If you more medical history or iformation to share, please feel free to add as a followup
HOpe this helps