Definitions of key inflammatory lesions:
(1) Palisading granuloma = an aggregate of histiocytes with parallel nuclei radiating around a necrotic nidus with neutrophils and nuclear dust; a granuloma < 1 mm in diameter is called a microgranuloma; a granuloma >= 1 mm in diameter is called a mcrogranuloma
(2) Diffuse granulomatous tissue = sheets of epithelioid histiocytes and multinucleated giant cells mixed with eosinophils, lymphocytes and plasma cells
(3) Leukocytoclastic capillaritis = fibrinoid necrosis, neutrophils and nuclear dust in the wall of a capillary
(4) Leukocytoclastic endovasculitis = fibrinoid necrosis, neutrophils and nuclear dust limited to the intima of a blood vessel (transmural inflammation absent)
Vascular lesions:
(1) microabscesses
(2) leukocytoclastic vasculitis
(3) leukocytoclastic capillaritis
(4) leukocytoclastic endovasculitis
(5) fibrinoid necrosis
(6) palisading granulomas
(7) fresh or organized thrombosis
Nonvascular lesions:
(1) palisading granulomas
(2) microabscesses
(3) diffuse granulomatous tissue
(4) neutrophilic infiltration of nasal glands
Key histologic features for making the diagnosis of Wegener's granulomatosis:
(1) vascular or nonvascular palisading granulomas
(2) microabscesses in vessel walls
(3) leukocytoclastic vasculitis
Signs of poor prognosis:
(1) leukocytoclastic vasculitis
(2) leukocytoclastic endovasculitis (seen only in fatal cases)
