Necrosis of WG

This photo (from the same patient whose lung was shown on the previous page) shows consolidation of the superior segment of the lower lobe. Within the consolidated area is a small cavity that resulted from necrosis (arrow).

Microabscess

The cavity shown above probably began as a microabscess, a microscopic focus of necrosis.

 

Shown here is a small collection of PMNs (arrow), a so-called microabscess. In this case it is surrounded by epithelioid cells and multinucleated giant cells, but these need not be present to diagnose a microabscess. Typically, these lesions are embedded in areas of granulomatosis.

Palisaded, granulomatous necrosis

Irregular (geographic) areas of bluish necrosis may also occur in areas of granulomatosis. These foci may represent enlargement or confluence of microabscesses. Sometimes, they are surrounded by palisading histiocytes; that is, elongated histiocytes lined up perpendicular to the necrosis (between arrows). Cavitation may occur.

If cavitation does not occur, this basophilic necrosis may be replaced by pink-staining fibrosis.

The term "pathergic necrosis" has been used to describe this peculiar necrosis that occurs in WG. This term refers to degeneration of collagen in vessels, airways, or consolidated parenchyma that evolves into the microabscess or palisaded, granulomatous necrosis [1].

The microabscesses and palisading necrosis shown here resemble infectious granulomas caused by mycobacteria or fungi even though the terminology used in WG differs. Therefore, it is mandatory to exclude an infectious etiology before diagnosing WG.

Reference

1. Yousem S. Bronchocentric injury in Wegener's granulomatosis: a report of five cases. Hum Pathol 1991; 22:535-540.

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