The incidence of intracranial metastases (also called brain metastasis A) refers to the transfer of tumor cells from other parts of the body into the skull. The peak age of onset is 20-50 years old, and there are more males than females. Brain metastases account for 10%-15% of intracranial tumors, and about 30% of patients with malignant tumors are found to have brain metastases during autopsy. The primary sites of metastases are lung, breast, gastrointestinal tumors and kidney cancer, among which lung cancer brain metastases account for 30%-40%, with small cell lung cancer and adenocarcinoma being the most common, and some articles reported that the brain metastasis rate of small cell lung cancer reaches 80% if the survival period is more than two years. Most brain metastases have a chronic onset, but the course of the disease often progresses rapidly. Most patients have symptoms of central nervous system dysfunction, including headache in about 50% of patients, as well as common nausea, vomiting, speech disorders, limb weakness, ataxia, cranial nerve palsy, etc. 25% of patients have optic papilledema. The site of disease is mainly in the blood supply area of the middle cerebral artery, which accounts for more than half of the disease, and it easily occurs at the junction of gray matter and white matter, and is more common in the frontal, temporal and parietal lobes and less common in the occipital lobe. Small cell lung cancer often occurs in cerebellar metastases. Intracranial metastases are multiple in 70%-80% of cases. Headache, vomiting, blurred vision, hemiparesis or monoparesis, slurred speech, unconsciousness, bilateral pupil narrowing, and increased intracranial pressure are symptoms. Brain metastases often metastasize to the skull via blood flow, subarachnoid space, lymphatic system or direct invasion. The site of tumor occurrence is related to the amount of blood supply and tissue volume in the disease area, which is usually found in the cerebral symphysis, and meningeal and cranial metastases can also be seen. Although there are many kinds of primary tumors in the brain, most of them are rare or even rare. The relatively common primary tumors in the brain are: glioblastoma and meningioma. The incidence of brain metastases is much higher than that of primary tumors, as the brain is one of the five organs (lung, liver, brain, bone and adrenal gland) that are prone to metastases. The clinical diagnosis of brain tumor mainly relies on MRI and CT examination of the brain. Due to the special location of the brain and the limitation of the skull, it is often difficult to obtain clear pathological evidence for the diagnosis of occupying brain lesions before treatment. It can only rely on imaging examination combined with clinical judgment. Although brain metastases may occur in various malignant tumors, the most common types clinically are brain metastases occurring in lung cancer, breast cancer and malignant melanoma, while other histological types are less common. In particular, brain metastases occurring from lung cancer account for almost a large proportion of all brain metastases, with lung adenocarcinoma and small cell carcinoma being more common. Brain metastases from lung adenocarcinoma account for approximately more than 50% of all brain metastases. Studies have shown that lung cancer is neurotropic and is prone to neurological metastases. Therefore, once an occupying brain lesion is detected clinically, a CT scan of the chest must be performed promptly. Conversely, if lung lesions are found, patients who are considered to be lung cancer should also have brain MRI examination in time. Brain metastases are mostly multiple metastases. Once the clinical diagnosis is established, the basic treatment mode is preferable to whole brain radiation therapy, based on which chemotherapy is used. At the same time, treatment of the primary tumor should be taken into account. In the past, it was thought that most chemotherapeutic drugs were difficult to cross the blood-brain barrier to exert therapeutic effects, and chemotherapy was not considered as the preferable treatment for brain metastases. However, in recent years, with the advancement of clinical research, new small molecule chemotherapeutic drugs and targeted therapeutic drugs have emerged, which can cross the blood-brain barrier, and some other studies have confirmed that the blood-brain barrier can be opened under the induction of some factors, chemotherapy for brain metastases is still useful. Especially for those patients with systemic multiple metastases, chemotherapy is the main treatment tool. Although brain metastases are mostly multiple, recent larger literature data show that about 1 /3 of brain metastases are solitary. According to the staging and treatment guidelines of various malignant tumors, brain metastases from organs are all in advanced stage, and there are no surgical guidelines. This concept is changing after years of clinical practice and some basic research. Some patients first presented with brain symptoms and were found to have brain occupancy. After timely management by brain surgery, the symptoms were relieved and the postoperative pathology confirmed that the brain metastasis was a brain tumor. Some patients with single brain metastases after lung cancer surgery have also achieved a good survival rate after undergoing surgery, and these clinical practices provide experiences that can be learned from surgical involvement in the treatment of brain metastases. However, surgical involvement in the treatment of brain metastases must be strictly justified and carefully implemented. For those histological types that are insensitive to radiotherapy (e.g. renal cancer, melanoma brain metastases, etc.), in conclusion, a correct understanding of MRI diagnosis and differential diagnosis of brain metastases can help in accurate clinical staging and reasonable treatment of tumors and prognostic assessment of patients. For brain metastases with a typical tumor history, MRI can mostly make a correct diagnosis. For intracerebral tumors with unclear medical history, the diagnosis of metastases needs to be made with caution and adequate differentiation from the primary intracranial tumor and other diseases in the brain. A positive attitude should be adopted for single resectable cases. VII. With the observation and research on the occurrence, development and metastasis rules of various malignant tumors, many malignant tumors exhibit specific metastatic pathways and manifestations. For example, malignant tumors of digestive system (esophageal cancer, cardia cancer, gastric cancer, colorectal cancer, etc.) mainly have liver metastasis; prostate cancer mainly has bone metastasis; liver cancer and kidney cancer mainly have lung metastasis; while lung cancer shows multi-organ metastasis, especially lung adenocarcinoma and small cell carcinoma are prone to brain metastasis, bone metastasis, liver metastasis, adrenal metastasis and intrapulmonary metastasis. Lung adenocarcinoma even accounts for more than half of all brain metastases, which deserves special attention. Physicians in thoracic oncology surgery, radiotherapy department and internal medicine should fully understand these characteristics and keep a good check during the diagnosis and treatment. The most common brain metastases originate from lung cancer, especially lung adenocarcinoma; 3. The diagnosis mainly relies on imaging examination combined with clinical examination, and MRI of brain is recommended; 4. 6.Surgical treatment for some brain metastases that are not sensitive to radiotherapy and single-site brain metastases has a positive effect and deserves attention; 7.Advocate comprehensive treatment and personalized treatment. For a long time, the medical profession has taken brain metastasis of malignant tumors as one of the criteria to judge the advanced stage of tumors. Once a patient is found to have brain metastases, it means that the patient enters the terminal stage of the disease; and the patient is even more frightened and waiting for death. However, clinicians fighting in the front line of tumor treatment have not given up their efforts. The ever-advancing imaging technology detects micro metastases in the brain earlier; the ever-improving radiation technology (linear gas pedal, X-ray knife, gamma knife) and the emergence of new chemotherapeutic drugs and targeted drugs; the surgical treatment of some single or resectable multiple metastases, etc. have enabled many patients to obtain better results, and some of them have achieved long-term survival (more than 10 years). Patients have achieved long-term survival (more than 10 years of survival), so that clinicians see hope and dawn.