Pulmonary Coccidioidomycosis Mimicking Aspergillosis Fungus Ball

The genus Coccidioides is composed of C. immitis and C. posadasii. Both can cause coccidioidomycosis and are geographically restricted to certain areas of endemicity. The histopathologic features in pulmonary coccidioidomycosis include necrotizing granulomatous inflammation and the presence of spherules, which is considered to be a key diagnostic finding. Cavitary lung disease containing a fungal ball with branching septate hyphae is an unusual funding in pulmonary coccidioidomycosis but is typical for aspergillosis. We present a case of 42 year old man who underwent wedge resection of the lung for a persistent cavitary lesion. The microscopic examination shows a fungal ball composed of acute-angle branching septate hyphae, consistent with a diagnosis of aspergillosis. However, cultures and molecular testing by DNA sequencing of the 28S ribosomal DNA gene confirmed the identification of C. posadasii. This finding highlights the importance of exposure history and organism identification by either conventional cultivation or molecular testing in rendering an accurate diagnosis.