The major categories of neuropathological conditions that the brain can sustain are: tumours, seizure disorders, cerebrovascular accidents, disorders of development, degenerative disorders, and disorders caused by infectious diseases. Tumour: a mass of cells whose growth is uncontrolled and that serves no useful function. Malignant tumour: a cancerous tumour, it lacks a distinct border and may metastasize. Metastasis: the processes by which cells break off tumours, travel through the vascular system, and grow elsewhere in the body. Tumours damage brain tissue by two means: compression and infiltration. Both benign and malignant tumours can cause damage by compression because they occupy space and push against the brain either destroying brain tissue or indirectly blocking the flow of cerebrospinal fluid and causing hydrocephalus. Tumours don"t arise from nerve cells (b/c they can"t divide) so they come other cells in the brain or from metastasis. Most serious types are metastases and the gliomas, which are usually very malignant/fast growing.