Coccidioides, Cryptococcus, or Blastomyces? A Diagnostic Dilemma Encountered During Frozen Section Evaluation

Intraoperative consultation via frozen section is an important part of modern day surgical pathology. Recognizing fungi in tissues on frozen and permanent sections is not always a simple task, and correctly identifying the agent can be a significant challenge, even for experienced microscopists. We present a case of a 17-year-old boy with chronic osteomyelitis involving the right proximal ulna. During an irrigation and debridement operation, a frozen section was sent to surgical pathology for evaluation. A limited patient history coupled with sparse organisms present in the frozen section led to the diagnosis of fungal osteomyelitis, favor Coccidioides. Follow-up permanent sections with special staining and successful fungal culture clarified the causal agent to be Blastomyces dermatitidis. The role of frozen sections is not to perfectly speciate the fungal pathogen but to describe the morphology and infectious process and provide a differential diagnosis of the candidate fungi. The importance of intraoperative culture in infectious cases cannot be understated, and it is the responsibility of pathologists to inform surgeons that tissue is needed for culture. A brief overview of Blastomyces, including histopathologic features and key microscopic differences from Coccidioides and Cryptococcus, is discussed.