Presentation
History of prostate cancer. Presents with several weeks of progressive lower extremity pain. Physical exam shows faint overlying erythema.
Patient Data
- lytic lesion centered within the medullary cavity of distal tibia, featuring wide zone of transition and absence of internal calcification to suggest osteoid or chondroid-type bone formation
- although indistinct, lesion appears to extend longitudinally, parallel to the medullary cavity
- no cortical erosion or periosteal reaction
- careful inspection of lateral view shows pretibial soft tissue thickening and subtle posterior displacement of adjacent musculature, more suggestive of local edema
- patchy and somewhat serpiginous T1/T2 hyperintensity within the medullary cavity of left tibia corresponds to lytic lesion on radiograph. Indeed, MR demonstrates a more proximal involvement than was apparent by radiograph. Again there is no evidence of cortical disruption
- post-contrast images show vague patchy hyperenhancement with central hypoenhancement within the lesion
- diffuse T1 hypointensity throughout the distal left tibial suggests a diffuse process which is replacing the normal T1-bright fatty marrow; STIR images show corresponding diffuse faint hyperintensity (best appreciated on coronal view and comparing to contralateral tibia) which is consistent with marrow edema
- thickening and STIR hyperintensity within the local hypodermal fat and intermuscular fascial planes suggests soft tissue edema/inflammation
Case Discussion
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