Brain metastases mainly originate from lung cancer, breast cancer, gastrointestinal tract tumors, genitourinary tract tumors, etc. Among them, 50% originate from lung cancer, and adenocarcinoma and undifferentiated carcinoma are more prone to intracranial metastases than squamous carcinoma. In addition, gastrointestinal tumors and pelvic tumors are prone to metastasis to the cerebellum.
Some patients may have stroke-like changes, and the course of the disease may develop more rapidly. If metastases are multiple, severe symptoms may appear early, and about 50% of patients have a history within six months. Most patients present with brain symptoms first, and some patients have a diagnosis of metastases, but the primary site is still uncertain. About 15-20% of patients present with cerebral symptoms after the primary lesion is diagnosed.
The common clinical symptoms are increased intracranial pressure and neurological dysfunction, with headache as the first symptom in about 50% of patients, accompanied by nausea and vomiting. 10% of patients have optic papilledema. Hemiparesis is a common sign, occurring in about 40% of patients. Subcortical metastases often occur as seizures, mostly limited seizures, with about 15-20% having the first symptom. Multiple brain metastases have a high incidence of epilepsy, and other symptoms include hemianesthesia, aphasia, and hemianopia. Metastases located in the cerebellum may have nystagmus, ataxia, and posterior group cranial nerve palsies.
The imaging of metastases has certain characteristics. CT non-enhanced lesions tend to be round-like or hypointense, or slightly dense. Most of them are located in the cerebral hemisphere cortex or subcortex, but also in the deep brain, thalamus, cerebellum and brainstem, with obvious brain edema. 60-70% of them are multiple foci of different sizes. After enhancement, brain metastases mostly show homogeneous or ring-strengthening, and the hypodense area within the ring is necrotic tissue, which does not strengthen. MRI is superior to CT, especially for resolving posterior cranial recess tumors.
The treatment of brain metastases is difficult and the efficacy is poor. Currently, comprehensive treatment, including surgery, radiotherapy and chemotherapy, is mostly advocated. However, for brain metastases, the most important thing is the choice of treatment timing, and it is necessary to have a full understanding and assessment of the systemic conditions, rather than just understanding the local changes. This is especially important when determining whether the patient will benefit from surgical treatment. It is important to consider not only the size, location, histologic features, age, neurologic status, and general condition of the intracranial metastases, but also the potential for occult intracranial metastases, the extent of cancer progression, response to treatment, and damage to other organs.
Many factors influence the survival of patients undergoing surgery for brain metastases, including the preoperative neurological classification, the diagnosis of the primary cancer and the interval between brain metastases, and most importantly, the degree of progression of the primary lesion, as the main cause of death in metastases is related to the progressive development of the primary cancer.
The current main treatments include: Surgery: Surgical removal of metastases can eliminate the source of brain edema. For those with obvious symptoms of increased intracranial pressure, surgical removal of the tumor can rapidly lower the cranial pressure to relieve the symptoms. For those with unclear diagnosis, histological diagnosis can be clarified. Surgical resection is the only treatment for tumors that are insensitive to radiation therapy.
Chemotherapy: Chemotherapy currently has a limited role in the treatment of brain metastases, although it can reduce the size of the tumor. The literature reports that 20-50% of patients treated with intravenous and arterial chemotherapy have minimal complete tumor disappearance. The reason for this ineffectiveness may be the difficulty of crossing the blood-brain barrier. However, for intracranial multiple metastases, it is not a lost treatment. Commonly used chemotherapeutic drugs include nitrogen mustard, cycloheximide, etc. According to the histological type of the primary tumor, appropriate anti-cancer drugs should be selected.
Hormone therapy: Hormone is effective in the treatment of most brain metastases. It is effective in reducing tumor-mediated peri-white matter edema, reducing surgical trauma edema and edema caused by radiation therapy. Hormone therapy alone can significantly reduce the neurological signs and symptoms of metastases, especially multiple brain metastases, so hormone therapy can provide short-term relief of clinical symptoms.
Radiation therapy: The combination of radiation therapy and hormone therapy can significantly prolong the survival rate of some patients with metastases and maintain the relative stability of the lesions. The response of metastatic tumors to radiation therapy depends on the sensitivity of the primary tumor to ionizing radiation. Radiation therapy is preferred for highly sensitive tumors such as lymphoma, germ cell tumors, and oat cell carcinoma. Moderately sensitive tumors include breast cancer, small cell lung cancer, inoperable, and those surviving more than three months should be given radiation therapy. There is no significant effect of radiation therapy for brain metastases from melanoma or sarcoma of the intestine, kidney, or thyroid.
Stereotactic surgery: With the development of stereotactic radiosurgery, γ-knife and X-knife have been widely used in the treatment of intracranial tumors indeed. Its accurate positioning, small radiation dose, and small damage to surrounding normal brain tissue make it a convenient and safe treatment method, but it cannot replace whole brain radiation therapy. As a systemic disease, metastases are often undetectable, so whole brain radiation therapy is necessary. Clinical treatment has proven that single lesion resection plus whole brain radiation therapy is superior to whole brain radiation therapy. Currently, surgical resection plus whole-brain radiation therapy is still the treatment of choice for single metastases. For deep and multiple metastases stereotactic radiation therapy is the preferred method.