Arthroconidia in lung tissue: an unusual histopathological finding in pulmonary coccidioidomycosis

Abstract

Coccidioides immitis/posadasii presents in mycelial form with branching hyphae and arthroconidia when cultured in the laboratory. On histopathology, the presence of endospore-containing spherules is considered diagnostic of coccidioidomycosis. Here we report an unusual case of coccidioidomycosis with hyphae and arthroconidia in pulmonary tissue sections. A 49-year-old male patient with intermittently treated pulmonary coccidioidomycosis sought treatment for residual pulmonary complaints. A cavity in the left upper lobe was seen on computed tomographic scan. Due to minimal improvement of symptoms despite treatment with fluconazole, a left upper lobectomy was ultimately performed. Coccidioides mimmitis/posadasii was identified by culture and DNA probe from the lobectomy specimen. The histopathology showed a fibro-cavitary lesion, with arthroconidia and hyphal structures, but no typical endospore-forming spherules. While uncommon, C. immitis/posadasii may present with hyphae and arthroconidia on histopathology. Pathologists should be aware of this unusual presentation; culture remains the most reliable method for definitive diagnosis.

Keywords: Arthroconidia; Coccidioides immitis; Coccidioides posadasii; Coccidioidomycosis; Histopathology of endemic fungi; Laboratory diagnosis of Coccidiodomycosis.

Figure 1

Cellophane tape mount of the mold from a Saboureaud Dextrose agar plate; stained with Lactophenol Cotton Blue (100X magnification), demonstrating alternating, barrel-shaped arthroconidia of Coccidioides species.

Figure 2

Representative H&E section (100× magnification) taken from the 7cm dominant lesion within the lobectomy specimen. The background is largely comprised of an amorphous, necrotic background with surrounding neutrophilic and lymphocytic inflammatory cells. Rare, but clearly visible alternating arthroconidia of Coccidioides are seen within the debris. Faintly-outlined spherical and ovoid endospores are also seen within the debris.

Figure 3

Higher-power representative H&E section (200× magnification) highlights the alternating pattern of the arthroconidia structures in greater detail.

Figure 4

Representative GMS section (100× magnification) highlights both arthroconidia and endospore structures of Coccidioides within the necrotic and inflammatory debris. Compared to the H&E sections, the details of the arthroconidia are somewhat obscured by the heavy silver-staining.