[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Blood vessels](https://durgical.com/en/general-pathology/areas/vessels/) › Vasculitis: classification and mechanisms

# Vasculitis: classification and mechanisms

- Topic

Vasculitis is inflammation of the vessel wall. The size of the vessels involved and the immune mechanism decide the disease.

Updated Nov 12, 2026

## Key points

- Large vessels (aorta and branches): giant cell arteritis (over 50) and Takayasu arteritis (under 50).
- Medium vessels (main visceral arteries): polyarteritis nodosa, Kawasaki disease, thromboangiitis obliterans.
- Small vessels, ANCA-associated (few immune deposits, ‘pauci-immune’): GPA (PR3-ANCA), MPA and EGPA (MPO-ANCA).
- Small vessels, immune complex: IgA vasculitis, cryoglobulinemic vasculitis, hypocomplementemic urticarial vasculitis, anti-GBM disease, lupus.
- Mechanisms: immune complexes, ANCA, anti-endothelial antibodies (Kawasaki), autoreactive T cells (granulomatous forms).
- Biopsy of an affected vessel confirms most forms; a long segment is needed when lesions are patchy.

## What it is

Vasculitis means inflammation of the vessel wall. It can come from direct infection of the wall or, more often, from immune mechanisms: immune complexes deposited in the wall, antineutrophil cytoplasmic antibodies (ANCA) that activate neutrophils, antibodies against endothelial cells, or T-cell mediated granulomatous inflammation. The consensus classification groups the non-infectious vasculitides by the calibre of vessel they mainly attack: large, medium or small; small-vessel disease is split into ANCA-associated and immune-complex types.

## Step by step

- A trigger (infection, drug, tumour antigen or unknown) starts an immune response.
- Immune complexes deposit in the wall, or ANCA bind primed neutrophils, or T cells react against wall antigens.
- Complement and Fc receptors call in neutrophils; their enzymes and oxidants destroy the wall (fibrinoid necrosis).
- The damaged vessel thromboses, bleeds or forms aneurysms; the tissue downstream becomes ischemic.
- Healing leaves fibrosis and narrowing of the vessel.

## Non-infectious vasculitis at a glance

| Disease | Vessel size | Key pathology | Key clue |
| --- | --- | --- | --- |
| [Giant cell arteritis](https://durgical.com/en/conditions/giant-cell-arteritis/) | Large (and medium) arteries of the head and aorta | Granulomatous arteritis with giant cells, fragmented elastic lamina | Over 50, headache, jaw claudication, high ESR, blindness risk |
| [Takayasu arteritis](https://durgical.com/en/conditions/takayasu-arteritis/) | Aorta and its main branches | Granulomatous arteritis, then fibrosis | Young women, weak arm pulses (‘pulseless disease’) |
| [Polyarteritis nodosa](https://durgical.com/en/conditions/polyarteritis-nodosa/) | Medium (and small) muscular arteries | Segmental fibrinoid necrosis, lesions of different ages, aneurysms | Kidney, gut, nerve, skin; spares lungs; hepatitis B in some |
| [Kawasaki disease](https://durgical.com/en/conditions/kawasaki-disease/) | Large to medium, especially coronary arteries | Transmural arteritis, coronary aneurysms | Child under 5, fever, mucocutaneous signs |
| [Thromboangiitis obliterans](https://durgical.com/en/conditions/thromboangiitis-obliterans/) | Medium and small arteries and veins of limbs | Inflammatory thrombus with microabscesses | Young heavy smokers, digital gangrene |
| [Granulomatosis with polyangiitis](https://durgical.com/en/conditions/granulomatosis-with-polyangiitis/) | Small to medium | Necrotizing granulomas plus vasculitis | Upper and lower airways and kidney; PR3-ANCA |
| [Microscopic polyangiitis](https://durgical.com/en/conditions/microscopic-polyangiitis/) | Small | Fibrinoid necrosis, lesions of one age, no granulomas | Lung capillaritis and glomerulonephritis; MPO-ANCA |
| [Eosinophilic granulomatosis with polyangiitis](https://durgical.com/en/conditions/eosinophilic-granulomatosis-with-polyangiitis/) | Small to medium | Eosinophil-rich necrotizing granulomas and vasculitis | Asthma, eosinophilia; MPO-ANCA in about half |
| [IgA vasculitis](https://durgical.com/en/conditions/iga-vasculitis/) | Small | Leukocytoclastic vasculitis with IgA deposits | Child, palpable purpura of buttocks and legs, arthralgia, abdominal pain, nephritis |
| [Cryoglobulinemic vasculitis](https://durgical.com/en/conditions/cryoglobulinemic-vasculitis/) | Small | Cryoglobulin deposits, leukocytoclastic vasculitis | Hepatitis C, purpura, low complement |

## Clinical notes

- Common signs: fever, weight loss, palpable purpura, mononeuritis multiplex, glomerulonephritis, lung hemorrhage, ischemic pain.
- ANCA testing, complement levels and hepatitis serology help sort the small-vessel forms.

## Memory aid

Size first, mechanism second: big pipes get granulomas, middle pipes get necrosis and aneurysms, small pipes are either ANCA or complexes.

## Test yourself

Think of the answer, then tap the question to see it.

## Which vasculitides are associated with PR3-ANCA and with MPO-ANCA?

PR3-ANCA: granulomatosis with polyangiitis. MPO-ANCA: microscopic polyangiitis and, in about half, eosinophilic GPA.

## Why are ANCA-associated vasculitides called pauci-immune?

Because the vessel lesions show little or no immunoglobulin and complement by immunofluorescence, unlike immune-complex vasculitis.

## What two large-vessel vasculitides are separated mainly by age?

Giant cell arteritis (over 50) and Takayasu arteritis (usually under 50, mostly young women).

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## Elsewhere in DurgiPedia

- [Type III hypersensitivity (immune complexes)](https://durgical.com/en/immunology/type-iii-hypersensitivity/)
- [Autoantibodies: the table to know](https://durgical.com/en/immunology/autoantibodies-the-table-to-know/)
- [Hypersensitivity: the four types compared](https://durgical.com/en/immunology/hypersensitivity-the-four-types-compared/)

## Connections

## Related 6

- [Large-vessel vasculitis: giant cell vs Takayasu](https://durgical.com/en/general-pathology/large-vessel-vasculitis-giant-cell-vs-takayasu/)
- [Medium-vessel vasculitis](https://durgical.com/en/general-pathology/medium-vessel-vasculitis/)
- [ANCA-associated vasculitis](https://durgical.com/en/general-pathology/anca-associated-vasculitis/)
- [Immune-complex small-vessel vasculitis](https://durgical.com/en/general-pathology/immune-complex-small-vessel-vasculitis/)
- [Infectious vasculitis and aortitis](https://durgical.com/en/general-pathology/infectious-vasculitis-and-aortitis/)
- [Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous](https://durgical.com/en/general-pathology/patterns-of-necrosis-coagulative-liquefactive-caseous-fat-fibrinoid-gangrenous/)

## Related conditions 12

- [Giant cell arteritis](https://durgical.com/en/conditions/giant-cell-arteritis/)
- [Takayasu arteritis](https://durgical.com/en/conditions/takayasu-arteritis/)
- [Polyarteritis nodosa](https://durgical.com/en/conditions/polyarteritis-nodosa/)
- [Kawasaki disease](https://durgical.com/en/conditions/kawasaki-disease/)
- [Granulomatosis with polyangiitis](https://durgical.com/en/conditions/granulomatosis-with-polyangiitis/)
- [Microscopic polyangiitis](https://durgical.com/en/conditions/microscopic-polyangiitis/)
- [Eosinophilic granulomatosis with polyangiitis (Churg–Strauss)](https://durgical.com/en/conditions/eosinophilic-granulomatosis-with-polyangiitis/)
- [IgA vasculitis (Henoch–Schönlein purpura)](https://durgical.com/en/conditions/iga-vasculitis/)
- [Cryoglobulinemic vasculitis](https://durgical.com/en/conditions/cryoglobulinemic-vasculitis/)
- [Cutaneous small-vessel (leukocytoclastic, hypersensitivity) vasculitis](https://durgical.com/en/conditions/cutaneous-small-vessel-vasculitis/)
- [Thromboangiitis obliterans (Buerger disease)](https://durgical.com/en/conditions/thromboangiitis-obliterans/)
- [Behçet disease](https://durgical.com/en/conditions/behcet-disease/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Vasculitis| Angiitis | MedlinePlus](https://medlineplus.gov/vasculitis.html) (MedlinePlus, US National Library of Medicine, 2025).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/vasculitis-classification-and-mechanisms/