In bone lesions, metastatic neoplasia and fungal infections are more frequently located in which region?

• A. Metaphyseal
• B. Epiphyseal
• C. Diaphyseal
• D. Skull

Answer: (C)

The main idea is that hematogenous spread to bone tends to seed areas with abundant medullary blood flow and accessible endosteal surfaces, making the long-bone shaft (the diaphysis) a frequent site for both metastatic tumors and fungal osteomyelitis. The diaphysis contains a large medullary cavity and rich vascular channels that can trap circulating malignant cells or fungal elements as they travel through the bloodstream. Once in the medullary space, these organisms or cells can proliferate and cause osteolysis along the diaphyseal region, sometimes extending toward the metaphysis and endosteum.

In contrast, the skull is a much less common site for hematogenous metastatic lesions or fungal osteomyelitis in small animals, and while the epiphysis can be involved, the diaphysis often represents the primary long-bone region where medullary seeding is most readily established in these processes.