Pulmonary vasculitis encompasses a group of pathological conditions characterized by systemic vasculitis involving the pulmonary vasculature. The core mechanism is destructive inflammation of the vessel wall leading to necrosis, thrombosis, and severe ischemia of the lung parenchyma.
Core PathologySystemic vasculitis with involvement of pulmonary vessels
PathogenesisImmune complex or ANCA-associated mechanisms
MorphologyTriad: necrotizing granulomas, vasculitis, and areas of necrosis
Key SyndromePulmonary-renal syndrome in combined organ involvement
Classification by Predominant Involvement
Depending on the extent of lung tissue involvement, these disorders are divided into three main groups:
Primary Pulmonary Vasculitides. Systemic vasculitides where the lungs are a primary target. These include granulomatosis with polyangiitis (Wegener granulomatosis), microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome).
Systemic Vasculitides with Potential Pulmonary Involvement. This group includes polyarteritis nodosa, microscopic polyangiitis, and Takayasu arteritis. Note: When a patient presents with simultaneous vascular involvement of the lungs and kidneys, the clinical term pulmonary-renal syndrome is used.
Secondary Vasculitides. These develop as complications of other disorders. They can occur secondary to systemic autoimmune diseases (systemic lupus erythematosus, sarcoidosis, Langerhans cell histiocytosis, lymphoproliferative disorders), severe infections, or following organ transplantation.
Pathogenesis
Pulmonary vasculitides are driven by two main immune mechanisms:
Immune Complex-Mediated. Circulating immune complexes form and subsequently deposit in blood vessel walls. This triggers complement activation, massive leukocyte recruitment, and an inflammatory cascade. This mechanism is most characteristic of systemic lupus erythematosus (SLE), polyarteritis nodosa, and other systemic connective tissue diseases.
ANCA-Associated. Vessel wall inflammation is directly linked to the production of antineutrophil cytoplasmic antibodies (ANCA).
Morphological Triad
The classic histopathological picture of pulmonary vasculitis consists of three mandatory elements:
Necrotizing Granulomas. These have irregular shapes. Their cellular composition includes neutrophils, lymphocytes, plasma cells, macrophages, eosinophils, and multinucleated giant histiocytes. Histiocytes may form characteristic palisading structures around the zone of necrosis. Diagnostic clue: sarcoid-like granulomas are not characteristic of this condition.
Vasculitis. This is distinctly destructive, affecting arteries, veins, and capillaries. Affected vessel walls exhibit polymorphous cellular infiltration, thrombosis, and fibrinoid necrosis.
Areas of Necrosis. These localize both within the granulomas themselves and in the surrounding lung parenchyma. Grossly, they resemble a geographic map and appear basophilic due to the accumulation of disintegrated nuclear debris. Necrosis forms via two mechanisms:
Heterolysis: neutrophil activation leads to the formation of microabscess-like structures.
Ischemia: ischemic pulmonary infarcts develop. This results from blood flow obstruction through vascular shunts from bronchial artery branches in the setting of widespread vasculitis. Similar ischemic necrosis may also be found in the brain.
Associated Morphological Findings
In addition to the classic triad, the lung parenchyma frequently demonstrates additional pathological processes. These include:
Alveolar hemorrhages.
Interstitial fibrosis.
Organizing pneumonia (OP) and bronchiolitis obliterans organizing pneumonia (BOOP).
Lipoid pneumonia and lymphoid hyperplasia.
Bronchial tree involvement: chronic or follicular bronchiolitis, bronchial stenosis, and bronchocentric granulomatosis.
Mnemonic
To quickly remember the morphological triad, use the rule "GVN": G — Granulomas (necrotizing), V — Vasculitis (destructive), N — Necrosis (geographic map-like).
Frequently asked questions
Which diseases cause pulmonary-renal syndrome?
Pulmonary-renal syndrome develops with simultaneous lung and kidney involvement. Key conditions include:
Microscopic polyangiitis — classically presents as pulmonary-renal syndrome, with renal and pulmonary pathology found in nearly all patients.
Granulomatosis with polyangiitis — affects the upper respiratory tract, lungs, and kidneys; necrotizing glomerulonephritis frequently develops.
Goodpasture syndrome — characterized by pulmonary involvement and rapidly progressive glomerulonephritis.
What ANCA types are identified in pulmonary vasculitis, and what are their target enzymes?
Two main types of antineutrophil cytoplasmic antibodies (ANCA) are recognized in pulmonary vasculitis, targeting enzymes found in primary granules of neutrophils and monocytes:
Cytoplasmic ANCA (c-ANCA) — target proteinase-3. These are characteristic of granulomatosis with polyangiitis.
Perinuclear ANCA (p-ANCA) — target myeloperoxidase. These antibodies are typical for microscopic polyangiitis and Churg-Strauss syndrome.
How do granulomatosis with polyangiitis and Churg-Strauss syndrome differ morphologically?
Morphological differences lie in granuloma composition, the nature of inflammatory infiltration, and the frequency of renal involvement.
Eosinophilic infiltration, granulomas at infarct margins
Renal Involvement
Necrotizing glomerulonephritis is common
Kidneys are rarely affected
Which vessel calibers are affected in microscopic polyangiitis?
Microscopic polyangiitis predominantly affects small-caliber vessels. The inflammatory process involves:
Arterioles;
Capillaries (including glomerular capillaries);
Venules.
Small- and medium-sized arteries may also be involved.
Which types of granulomas are atypical for pulmonary vasculitis?
Sarcoid-like granulomas are atypical. Vasculitis is classically characterized by irregular necrotizing granulomas where histiocytes form palisading structures around the necrotic zone.
What type of necrosis develops in the vessel wall during pulmonary vasculitis?
Fibrinoid necrosis develops within the vessel wall, accompanied by thrombosis and marked polymorphous cellular infiltration.
What causes ischemic pulmonary infarcts in vasculitis?
Ischemia results from widespread involvement of the pulmonary and bronchial arteries, leading to the occlusion of blood supply via vascular shunts and subsequent tissue infarction.
What does the term "pulmonary-renal syndrome" mean?
This clinical term is used when systemic vasculitis simultaneously affects the vascular beds of both the lungs and the kidneys.
Go deeper
Granulomatosis with polyangiitis: specific patterns of organ involvement
Churg-Strauss syndrome: the role of eosinophils in pathogenesis
Microscopic polyarteritis and polyangiitis: morphological distinctions
Mechanisms of ANCA-associated vasculitis development
Bronchocentric granulomatosis and bronchiolitis obliterans