Vasculitis is inflammation and necrosis of blood vessel walls, classified by the 2012 revised Chapel Hill Consensus Conference (CHCC) nomenclature according to the predominant size of affected vessels. Large vessel vasculitis (LVV) affects the aorta and its major branches: giant cell arteritis (GCA/temporal arteritis) targets the extracranial branches of the carotid artery (especially the temporal artery) and the aorta in patients >50 years, causing granulomatous inflammation with multinucleated giant cells that narrow the vessel lumen and risk ischemic complications including permanent vision loss from anterior ischemic optic neuropathy (AION); Takayasu arteritis affects the aorta and its primary branches in patients <40 years, causing stenosis, occlusion, or aneurysm formation (pulseless disease). Medium vessel vasculitis (MVV) includes polyarteritis nodosa (PAN), which causes segmental necrotizing inflammation of medium muscular arteries (particularly renal, mesenteric, and coronary arteries) with microaneurysm formation visible on angiography -- PAN is NOT associated with ANCA and does NOT affect the lungs or glomeruli (distinguishing it from ANCA-associated vasculitis); Kawasaki disease affects medium-sized arteries with predilection for coronary arteries in children. Small vessel vasculitis (SVV) is divided into ANCA-associated vasculitis...