Intracranial tumors, sometimes referred to as “brain tumors”, are tumors located within the closed cavity (cranial cavity) surrounded by the skull. This type of tumor is primarily the province of neurosurgeons. It should be noted that intracranial tumors are different from “head tumors”, which includes not only the cranial cavity, but also the extra-cranial space such as face, eye, mouth, etc. Most of the extra-cranial space is not the specialty of neurosurgeons, but belongs to ophthalmology, dentistry, ENT, etc. Most of the extra-cranial space is not the specialty of neurosurgeons, but belongs to ophthalmology, stomatology, ENT and other specialties. Intracranial tumors can be divided into benign and malignant tumors, however, in some cases, benign and malignant are not clear-cut, some tumors are between benign and malignant, while some benign tumors are easy to recur after surgery and are cool like malignant tumors. Therefore, all tumor patients are advised to review regularly after surgery or other treatments to be alert to tumor recurrence. The diagnosis of benign and malignant tumors and their specific types depends on “pathological examination”, which means that after surgery, the cut tumors are sent to the pathology department, and the specialized staff will cut the tumors into thin slices and carefully observe the morphology of tumor cells under the microscope to make the final diagnosis of the nature of the tumors, which is called “confirm diagnosis”. In patients without surgical treatment, doctors will give a preliminary diagnosis based on CT or MRI film, which is not confirmed by pathology, and can only be called “clinical diagnosis”, most of the time, clinical diagnosis and pathology diagnosis are generally consistent, but sometimes clinical diagnosis still has errors, and only pathology diagnosis is the most authoritative. Only pathology diagnosis is the most authoritative. The most common malignant tumor is glioma, which also includes metastatic cancer, lymphoma, and follower cell tumor. The most common benign tumor is meningioma, followed by pituitary tumor, and others are nerve sheath tumor, hemangioblastoma, and lipoma. There are also some lesions with the word “tumor” in their names, but they are not strictly tumors, mainly congenital vascular malformations, including cavernous hemangiomas and aneurysms. There are also some “cyst” lesions, such as epidermoid cyst, dermatomal cyst, arachnoid cyst, etc. Most of them are also congenital and usually grow very slowly, but the symptoms may be similar to tumors, so the treatment is similar to tumors. In terms of treatment, malignant tumors generally require surgery plus radiotherapy or chemotherapy, and a few types may be treated without radiotherapy or chemotherapy. Benign tumors are mainly treated by surgery, but benign tumors that are only partially removed but not completely removed often require the addition of radiotherapy. Next, we will briefly mention some of the most common intracranial tumors (a) Glioma Glioma is the most common intracranial malignant tumor and the most common intracranial tumor, accounting for 40-50% of all intracranial tumors. Glioma is subdivided into many types, including astrocytoma, oligodendroglioma, ventricular meningioma, mesenchymal astrocytoma, glioblastoma, and so on. Patients do not need to know these specific terms in detail, but only the classification of gliomas. Gliomas are generally malignant tumors, but the degree of malignancy varies greatly, and they are internationally classified as grades 1-4, with grade 1 being the most benign and grade 4 being the most malignant. In terms of incidence, grade 4 is the most common, grade 3 is the second most common, and grade 1 is the least common. Grade 1 gliomas include hairy cell astrocytoma and ganglion cell tumor, etc. If the surgery is clean, radiotherapy is not necessary, and the prognosis is good. Grade 2 gliomas include astrocytoma, oligodendroglioma and ventricular meningioma, etc. Depending on the condition, radiotherapy or chemotherapy may be required after surgery, and if the surgery is complete, the 5-year survival rate can reach 80%. Grade 3 glioma includes mesenchymal astrocytoma, mesenchymal oligodendroglioma, mesenchymal ventricular meningioma, etc., which are more malignant and require radiotherapy and chemotherapy after surgery. grade 4 glioma is mainly glioblastoma, also known as glioblastoma multiforme, which is extremely malignant and has a poor prognosis, and requires radiotherapy and chemotherapy after surgery. (2) Metastatic cancer Metastatic cancer refers to the case where malignant tumors from other parts of the body (such as lung cancer, intestinal cancer, etc.) metastasize into the skull. For patients with advanced cancer, intracranial metastasis is very common. The general treatment principle is that if the primary cancer (lung cancer, etc.) is controlled and stable after treatment, no other metastases are found except for the head, and the intracranial metastases are single rather than multiple, surgery can be considered at this time, and radiotherapy can be considered after surgery according to the specific type of the primary cancer, with the hope of obtaining a better prognosis; if the above criteria are not met, often only radiotherapy can be given and the prognosis is poor. However, we also encountered many patients with good general condition, no serious symptoms, no tumor found anywhere outside the head examination, only tumor found in the head, and pathological diagnosis of metastatic cancer after surgery. In this case, most of the time (except for a few cases), the pathology department can only give the diagnosis of “metastatic cancer” in a very general way, and cannot precisely determine where the tumor is metastatic from. The reason for this is that the primary cancer is very small and does not cause any symptoms and cannot be seen on CT films, while the tumor cells have metastasized early. This situation is more tangled, and because the primary cancer is not found, targeted radiotherapy cannot be administered. The usual practice is to perform frequent whole-body examinations after surgery until the primary cancer is found to grow to the extent that it can be seen on the film, and then treat the primary cancer. (iii) Intracranial lymphoma Lymphoma can occur in many parts of the body, and only intracranial lymphoma is mentioned here. According to the results of pathological examination, lymphoma can be subdivided into types, and there are high and low malignant degrees. Treatment is mainly based on chemotherapy, and radiation therapy may be added depending on the specific type. This encounters a dilemma: should intracranial lymphoma be operated or not? In pure theory, a fully diagnosed lymphoma does not require surgery, only chemotherapy or radiation therapy, but in practice, such a “confirmed” diagnosis without surgery and pathology is almost non-existent. If lymphoma is not actually lymphoma but is treated with chemotherapy as lymphoma, the disease will be seriously delayed and the only means to obtain a “definitive diagnosis” is surgery and subsequent pathological examination. Therefore, the internationally accepted method is: surgery should be done, but it is not required to cut the whole tumor, and it is enough to take a little tumor for pathological examination, and then chemotherapy and radiotherapy should be carried out according to the pathological results. (D) Meningioma Most meningiomas are benign tumors, but a very small percentage of them are malignant. Generally speaking, meningioma grows on the peripheral “meninges” of the brain, inside the brain and outside the skull. Depending on the specific location, meningiomas can be divided into convex meningiomas and skull base meningiomas. Convex meningiomas are located superficially on the surface of the skull and are relatively easy to operate on, while meningiomas at the base of the skull are located deeper on the base of the brain and are more difficult to operate on. Treatment is mainly surgical and radiotherapy is not needed. In a few cases, the tumor is close to important blood vessels and nerves, which makes surgery very difficult and prevents total excision of the tumor, and then radiotherapy is needed. （Pituitary tumor is a tumor located in the pituitary gland, more than 99% of which are benign. The pituitary gland is a normal organ of human being, with a diameter of 1-50 px and a deep location, probably at the back of the nasal cavity next to the brain. The normal function of the pituitary gland is to produce a variety of hormones such as prolactin, growth hormone, gonadotropin, and corticotropin, which regulate a variety of human physiological functions. The symptoms of pituitary tumor are manifested in two aspects: on the one hand, the compression of peripheral nerves and brain tissues by the tumor, including blurred vision, double vision and headache, and on the other hand, abnormal secretion of pituitary hormones, including breast lactation, low sexual function, facial changes and abnormal obesity. Treatment is mainly transnasal minimally invasive surgery, and a few larger tumors require craniotomy. For prolactinoma pituitary tumors, oral medication can be considered. Endoscopic surgery is a new technique developed in recent years, which is an “upgraded” version of microscopic surgery and has better minimally invasive effect, and is now routinely performed in a few large hospitals in China. It should be added that pituitary tumors have a high recurrence rate among benign tumors and must be reviewed regularly. （Nerve sheath tumors are benign tumors that grow at the roots of these “wires”, which are the nerves in the brain that control human physiological functions. The most common intracranial tumors are auditory neuroma and trigeminal nerve sheath tumor. The main symptoms include compression of brain tissue, including headache and vomiting, and neurological dysfunction, such as hearing loss and deafness in the case of auditory neuroma and facial numbness or pain in the case of trigeminal nerve sheath tumor. Treatment is still mainly surgical. Since the tumor grows right on top of the nerve, the corresponding nerve function cannot be preserved after surgery, and symptoms such as hearing loss, facial palsy and facial numbness will occur.