Given the patient's history of prostate cancer, the lytic lesion seen on initial radiograph was thought to represent an atypical presentation of metastasis (bone metastasis from prostate cancer are more commonly sclerotic and more central in location). However, the aggressive appearance - a wide zone of transition, soft tissue swelling, and subtle longitudinal "burrowing" extension following the medullary cavity - is nonspecific and could represent osteomyelitis, myeloma, or lymphoma.

MRI confirms a more extensive and inflammatory process with surrounding marrow and soft tissue edema. The lesion itself remains indeterminate by MRI, but patchy peripheral hyperenhancement with central hypointensity suggest central necrosis.

Patient underwent CT-guided bone biopsy for definitive diagnosis:

Histopathology

• Microscopic description: mixed inflammatory infiltrate comprised of neutrophils and histiocytes as well as foamy epithelioid to spindle cells. Five single antibody immunostain procedure(s) with appropriate staining controls were performed to further evaluate the medullary constituents.  Pancytokeratin, cytokeratin 7, cytokeratin 20, NKX3.1, CDX2, and S100 are negative, excluding the presence of metastatic carcinoma.  CD68 highlights a histiocytic infiltrate.  A GMS stain, performed with appropriate controls, highlights budding yeast forms
• Impression: Acute and chronic osteomyelitis with fungal forms identified

Laboratory studies

• direct stain: abundant polymorphonuclear leukocytes, no organisms
• bacterial culture: No growth (4x)
• fungal culture:  Blastomyces dermatitidis \ gilchristii