Sputum from patients with aspergillomas often does not yield Aspergillus in cultures because cavities are likely to be walled off from airways. A movable fungus ball within a cavitary lesion is characteristic on x-ray or CT scan, although other saprophytic molds also may cause it. Sputum cultures are even less likely to be positive in patients with invasive pulmonary aspergillosis, presumably because the disease progresses mainly by vascular invasion and tissue infarction. Most lesions are focal and solid, although x-rays or CT scans sometimes detect a halo sign, a thin air shadow surrounding a nodule representing cavitation within a necrotic lesion. Diffuse, generalized infiltrates occur in some patients.
Progression usually is extremely rapid.
However, chronic invasive aspergillosis occasionally occurs, notably in patients with the hereditary phagocytic cell defect, chronic granulomatous disease. Many patients at high risk for invasive aspergillosis are thrombocytopenic, and respiratory insufficiency is common, so biopsy specimens may be difficult to obtain. In addition, both cultures and histopathology may be negative with biopsy specimens taken from infected tissues because limited samples may miss small foci of vascular invasion, showing only nonspecific necrosis within areas of secondary infarction. Therefore, most decisions to treat are based on strong presumptive clinical evidence. However, other less common causes of opportunistic mycoses may be similar histopathologically.