Aspergillus is a ubiquitous fungus, found throughout nature which may cause disease in susceptible hosts when inhaled. The risk groups for invasive aspergillosis are patients who have severe, prolonged granulocytopenia secondary to hematologic malignancy; hematopoietic stem cell/solid organ transplant recipients; and patients who are taking high-dose corticosteroids. Rarely, persons who have HIV infection develop aspergillosis.  Aspergillus fumigatus is the most important species that causes infection in humans.

 

Angioinvasive aspergillosis results when Aspergillus invades the pulmonary vasculature and causes thrombosis, pulmonary hemorrhage, and infarction. It is characterized at histologic analysis by the invasion and occlusion of small- to medium-sized pulmonary arteries by fungal hyphae that lead to the formation of necrotic hemorrhagic nodules or pleural-based, wedge-shaped, hemorrhagic infarcts.

 

 CXRs often are abnormal, but nonspecific, and reveal patchy segmental or lobar consolidation or multiple, ill-defined nodular opacities.

 

Characteristic CT findings consist of nodules that are surrounded by a halo of ground glass attenuation (“halo sign”) or pleural-based, wedge-shaped areas of consolidation. These findings correspond to hemorrhagic infarcts. In severely neutropenic patients, the halo sign is highly suggestive of angioinvasive aspergillosis; however, a similar appearance has been described in several other conditions, such as candida, mucor, herpes simplex, CMV, and Kaposi\'s sarcoma.

 

As the patient\'s immune system recovers, about 2 weeks after the onset of infection, CXR or CT may demonstrate an “air crescent sign,” corresponding to necrotic lung around retracted infarcted lung. Although this finding is not specific for angioinvasive aspergillosis, it is highly characteristic in the proper clinical setting, especially when the initial lesion is consolidation or a mass. Air crescent formation was shown to be associated with improved survival.