Histology with Hematoxilin and Eosin (H&E) staining. A low power objective (A, 10X) showed areas of synovium with necrosis (thin arrow) and granulomatous inflammation (thick arrowhead). At a higher magnification (B, H&E stain, 40X), a spherule (arrow) containing endospores could be clearly identified. Spherules and endospores are also visible by the Gomori’s methenamine silver (GMS) stain (C, 40X) and by the acid fast bacillus (AFB) stain (D, 60X). The size and morphology of these structures is consistent with Coccidioides immitis.