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Invasive Aspergillosis with Air Crescent

Gregory D N Pearson, MD, PhD
Andetta R Hunsaker, MD

May 16, 1996

Presentation

A 66-year-old man, having undergone chemotherapy for acute myelogenous leukemia, presented with neutropenia and fever.

Imaging Findings

Plain radiograph of the chest, PA view
Plain radiograph of the chest, lateral view
Plain radiograph of the chest, two weeks later
Magnification of latter radiograph

Posteroanterior (PA) and lateral views of the chest demonstrate right upper lobe consolidation as well as the stigmata of prior cardiac surgery. A posteroanterior view obtained two weeks later demonstrates a smaller region of consolidation with the new finding of a crescentic lucency (arrow) superiorly.

Differential Diagnosis

Findings from the original study are consistent with a right upper lobe pneumonia (bacterial of fungal etiology most likely). Given the history provided, the air crescent sign visible on the later study is virtually pathognomonic of invasive aspergillosis. Other entities that can occasionally produce air crescents include:

Diagnosis

Invasive aspergillosis with developing air crescent

Discussion

Aspergillosis fumigatus   is a ubiquitous dimorphic fungus that causes several types of pulmonary illness. Manifestations are primarily dependent upon the immune status of the patient. In noninvasive aspergillosis, fungus colonizes a preexisting cavity, bronchiectatic bronchus, or bulla and forms a mycetoma, or fungus ball. In semi-invasive aspergillosis, patients are mildly immounosuppressed due to sarcoidosis, alcoholism, or other debilitating illness. The fungus begins growing as an infiltrate, but over several months cavitates to form a thick-walled cavity with a mycetoma. In allergic bronchopulmonary aspergillosis, fungal spores elicit a hypersensitivity reaction in the tracheobroncheal tree, usually in asthmatics. This leads to the production of mucus which traps the fungal hyphae in the airway, eventually leading to mucoid impation.

The development of invasive aspergillosis, as in the current patient, requires severe impairment of host defense mechanisms, usually due to acute leukemia and granulocytopenia from chemotherapy. Fungus invades the lung, causing consolidation, and invades the blood vessels, causing pulmonary infarction. If cavitation and air crescent formation occurs, it is usually at the time that the patient's granulocyte count begins to recover. Air crescent formation is a good prognostic sign, with survival in one series 67% with air crescent and 8% without. Unlike noninvasive aspergillosis, the mass within the cavity is typically necrotic lung tissue and only rarely a true mycetoma.

References

1. Freundlich IM, Bragg DG. Radiologic approach to diseases of the chest. Baltimore: Williams and Wilkins 1992; 279-81.

2. Gefter, et al. Invasive pulmonary aspergillosis and acute leukemia: limitations in the diagnostic utility of the air crescent sign. Radiology 1985; 157:605-10.

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