"Primary" angiitis/vasculitis of the central nervous system (PACNS) is said to be present if there is no underlying cause. The exact mechanism of the primary disease is unknown, but the fundamental mechanism of all<unk> es is autoimmunity. Other possible secondary causes of<unk>  are infections, systemic auto-immune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis, medications and drugs (amphetamine, cocaine and heroin), some forms of cancer (lymphomas, leukemia and lung cancer) and other forms of systemic<unk>  such as granulomatosis with polyangiitis, polyarteritis nodosa or Behçet's disease. It may imitate, and is in turn imitated by, a number of other diseases that affect the blood vessels of the brain diffusely such as fibromuscular dysplasia and thrombotic thrombocytopenic purpura.
Cerebral vasculitis
Infectious intracranial aneurysm
Cerebral atherosclerosis
Meningism
Giant cell arteritis
Cerebral amyloid angiopathy
Intracranial aneurysm
Cerebral vasospasm