Central nervous system (CNS) vasculitis encompasses a group of disorders characterized by inflammation and destruction of blood vessel walls within the brain and/or spinal cord, leading to vessel wall damage, stenosis, occlusion, and/or aneurysm formation with consequent ischemic or hemorrhagic injury to the nervous system. The most important entity in this group is primary angiitis of the central nervous system (PACNS), an idiopathic inflammatory disease confined exclusively to the CNS vasculature without systemic involvement. PACNS accounts for approximately 1% of all systemic vasculitides and has an incidence of approximately 2.4 per 1,000,000 person-years. CNS vasculitis can also occur secondary to systemic vasculitides (polyarteritis nodosa, granulomatosis with polyangiitis/GPA, eosinophilic granulomatosis with polyangiitis/EGPA, microscopic polyangiitis, Behcet disease, giant cell arteritis), systemic autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, sarcoidosis), infections (varicella-zoster virus is the most common infectious cause, HIV, syphilis, tuberculosis, fungal infections), drugs (cocaine, amphetamines), and malignancy (lymphomatoid granulomatosis, intravascular lymphoma). The pathogenesis of PACNS involves immune-mediated inflammation of the walls of small and medium-sized leptomeningeal and parenchymal arteries. The inflammatory infiltrate is predominantly composed of lymphocytes (CD4+ T cells predominate)...