Invasive pulmonary aspergillosis and acute leukemia. Limitations in the diagnostic utility of the air crescent sign.

The air crescent sign is regarded as an important diagnostic finding in invasive pulmonary aspergillosis (IPA). This study examined the incidence, clinical importance, and natural history of air crescents in 25 patients with acute leukemia and IPA. Twelve (50%) of the patients had cavities (ten with an air crescent) that appeared an average of 15 days after the initial infiltrate. The diagnostic utility of the air crescent sign was relatively minor; cavities developed after the diagnosis was established in 50% of cases and after therapy was started in 75% of cases. In each case, the pneumonia improved at the time of cavitation. In six patients (50%), the cavities resolved over 2-8 months. Three patients (25%), however, experienced massive hemoptysis. Air crescent formation, previously shown to be dependent on granulocyte recovery, was associated with improved survival (67%) compared with the group without cavitation (8%). In the latter group, the pneumonia in ten (77%) of 13 patients progressed to diffuse disease. In patients with leukemia, the diagnostic value of the air crescent sign is limited by cavities that develop relatively late, as the infection improves after white blood cell recovery; cavities that do not occur in patients who remain neutropenic; and associated hemorrhage, at times life-threatening, that obscures the air crescent. The diagnosis of IPA should not await observation of air crescents in these patients.