Histopathological implications of Aspergillus infection in lung

Abstract

This paper opens with a discussion on the significance of invasive fungal infections in advanced contemporary medicine, with an emphasis on the intractability of disease management and the difficulties of diagnosis. This is followed by a discussion concerning classification, histopathological features, and pathophysiology. While it has been largely accepted that Aspergillus species is recognized by cellular receptors and attacked by neutrophils, the radiological and macroscopic findings linking infection with neutropenia remain unconfirmed. In an effort to gain a better understanding of the pathophysiology and pathogenesis of invasive aspergillosis, we wish to emphasize the utility of radiological and histopathological examinations since these can provide detailed information on the extremely complex interaction between the causative microbes and tissue responses. A review of noninvasive or semi-invasive aspergillosis is also provided, with particular emphasis on chronic necrotizing pulmonary aspergillosis, which is recognized as a transition form of simple pulmonary aspergilloma and invasive pulmonary aspergillosis, although few findings have been reported in this area.

Figure 1

Invasive pulmonary aspergillosis, discrete nodule. (a) The nodule comprises coagulation necrosis of the lung tissue (‡) and acute hemorrhage usually accompanies the necrosis (¶) and may mimic a halo sign on CT (Hematoxylin-Eosin, X20). (b) Zone formation (mimicking an annual ring) of hyphae aligned in a radial pattern. Few inflammatory infiltrates are accompanied in the lesion (Hematoxylin-Eosin, X200). (c) Acute hemorrhage can be seen. No hyphae can be observed.

Figure 2

Invasive pulmonary aspergillosis, fused lobular consolidation. (a) The lesion comprising a fusion of solidified lobules is seen on a section of lung (white arrow head). The necrotic cavity is usually present at the center. (b) Ordinary bronchopneumonia can be seen (Hematoxylin-Eosin, X20). (c) Alveoli present due to the invasion of hyphae are filled with neutrophils (Hematoxylin-Eosin, X200). (d) Growth of fungus is present in the airspace (GMS, X400).

Figure 3

Invasive pulmonary aspergillosis with infarction. (a) There is a sharply demarcated nodule on a section of the lung (white arrow head). (b) Fungus hyphae can be seen in the vessel. Coagulation necrosis can be seen surrounding the vessel (Hematoxylin-Eosin, X20). (c) The pulmonary structure is not destroyed by the fungi (Elastica van Gieson, X20). (d) Hyphae aligned in a radial pattern within the vessel and airspace (GMS, X20).

Figure 4

Invasive pulmonary aspergillosis with huge embolism. There is a huge embolism in the large vessel (black arrow head) with obstructive pneumonia. This was a case with long-term followup, and the annual ring can be seen in the embolism.

Figure 5

Simple pulmonary aspergilloma. There is a preexisting cavity (black arrow head) and few changes surrounding the cavity.

Figure 6

Chronic pulmonary aspergillosis. There is a cavity filled with fungus (white arrow head) surrounded by the secondary organization.