Brain tumor formation time needs to depend on the type of tumor, there is no fixed value, and the formation time fluctuates approximately between a few months to a few years. 1. Benign intracranial tumors, such as meningiomas, tumors in the pterygoid region, acoustic neuromas, epidermoid cysts, dermoid cysts, and so on. They are slow-growing and may take three to five years or even longer to form. When they increase in size, they will compress the surrounding brain tissues and cause brain dysfunction. Generally, it can be relieved after surgical resection, and the possibility of recurrence and metastasis is very small. 2. Intracranial malignant tumors, such as glioma, medulloblastoma, ventricular meningioma, brain metastases, etc., grow fast and may be formed in a few months, with high degree of malignancy, and they will be transferred to other parts of the body, which is harmful to the human body.