Figure 14-48.

Morphologic Features of Fungi That May Infect the Central Nervous System.

A,Blastomyces dermatitidis, 8 to 25 mm in diameter, broad-based budding spherical yeast-like microbes, intracellular or extracellular location. H&E stain. B,Cryptococcus neoformans. In this illustration the microbe is surrounded by a mucinous capsule that is stained with Mayer's mucicarmine. The capsule varies in width but can be so thick as to give the microbe an overall diameter of 30 mm. The microbe without its capsule is 5 to 20 mm in diameter. The capsule does not stain with H&E, thus causing the microbe to appear to be surrounded by a clear halo (see Fig. 14-50, A). The microbes are oval to spherical but may be crescentic or cup shaped in routine mucicarmine- and H&E-stained sections. Dehydration that occurs during processing of the tissue to embed it in paraffin causes this shrinkage and distortion. Mayer's mucicarmine stain, aqueous wet mount. C,Histoplasma capsulatum, located intracellularly, is spherical to elongated, 5 to 6 mm in diameter. H&E stain. D,Coccidioides immitis, spherules (20 to 30 mm in diameter) containing endospores (<5 mm in diameter), can be intracellular or extracellular. H&E stain.

(Courtesy Dr. M.D. McGavin, College of Veterinary Medicine, University of Tennessee.)