Brain metastasis of lung cancer is caused by hematogenous spread of lung cancer to the brain. Brain metastasis typically presents with symptoms such as headaches, nausea, and vomiting, including projectile vomiting. The headaches may be severe, and there may be abnormalities in sensory perception and motor function, possibly accompanied by seizures, mental confusion, olfactory disturbances, visual impairments, and other symptoms. The specific symptoms can vary depending on the location of the metastasis in the brain. However, most patients experience headaches, nausea, and vomiting. Individual differences are significant, and it's important to analyze the specific issues and the specific areas of the brain affected.