The air crescent sign of invasive pulmonary mucormycosis in acute leukemia.

An unusual radiographic sign of crescentic cavitation appeared in a case of invasive pulmonary mucormycosis complicating the treatment of a patient with acute myelogenous leukemia and having a normal admission chest radiograph. The first manifestation was a large, wedge-shaped pleural-based consolidation, which evolved about 10 days later into a fungus ball-like lesion, usually known as the air crescent sign. Amphotericin B and 5-fluorocytosine, which were initiated immediately after appearance of the sign, proved to be effective, probably in association with hematologic improvement. Transbronchial lung biopsy was not only helpful in establishing a definitive diagnosis, but also suggested that an intracavitary mass could have resulted from pulmonary infarction. This experience thus showed that the sign may appear in greater frequency in mucormycosis as well as in aspergillosis, and may be useful as a clinical index for initiating antifungal therapy in immunocompromised patients.