Brain cysts do not turn into brain tumors. Brain cysts, also known as arachnoid cysts, are benign lesions that develop congenitally, with the contents of cerebrospinal fluid and the walls of the cysts being the arachnoid membrane. Most patients with arachnoid cysts do not have obvious clinical symptoms, and they are found during physical examination or other reasons for head CT and MRI. The cysts progress very slowly and most of them are accompanied for life. And brain tumor refers to the tumor of brain parenchymal cells, originating from various tissues in the skull, caused by the proliferation of brain parenchymal cells, there are benign and malignant tumors, fast-growing tumors can be hemorrhage, necrosis, cystic degeneration within the tumor, but it is a different nature of the lesion with the brain cysts, and there is no inevitable connection between the two, so the brain cysts will not turn into brain tumors.