Which statement correctly defines endosteal lysis and periosteal-surface lysis only?

• A. Periosteal-surface lysis only indicates endosteal invasion by malignant neoplasm.
• B. Endosteal lysis = primary malignant bone neoplasia, round cell neoplasia, metastatic neoplasia, osteomyelitis; nonspecific but aggressive.
• C. Both forms indicate the same prognosis.
• D. Neither form is associated with aggressive disease.

Answer: (B)

Endosteal lysis is a loss of bone from the inner cortical surface toward the medullary cavity, which signals an active, destructive process in bone. When this pattern is present, the lesion is typically aggressive, and the differential broadens to include primary malignant bone tumors, round cell neoplasia (like lymphoma or plasmacytoma), metastatic disease, and osteomyelitis. It’s nonspecific because many different conditions can cause endosteal destruction, but its presence strongly points to an aggressive process rather than a benign one.

That same sense of aggressive pathology is why the statement pairing endosteal lysis with those categories is the best fit for defining endosteal lysis and periosteal-surface lysis: it accurately captures the association with malignant or inflammatory aggressive processes. Other options mischaracterize the prognostic implications or the relationship between the two bone-destructive patterns, since aggressive disease can manifest with endosteal involvement and periosteal surface changes, and neither form is reliably synonymous with a single disease or with indolent behavior.