Endosteal lysis on imaging is most consistent with which processes?

• A. Extraskeletal soft tissue invasion by tumor only
• B. Healing fracture
• C. Endosteal lysis is associated with primary malignant bone neoplasia, round cell neoplasia, metastatic neoplasia, osteomyelitis; nonspecific but aggressive
• D. Benign bone cysts

Answer: (C)

Endosteal lysis indicates aggressive destruction along the inner surface of the bone cortex, a pattern that points to an invasive, often malignant or inflammatory process rather than a simple or benign change. When you see this feature on imaging, think of conditions that actively erode bone—primary malignant bone neoplasia, round cell neoplasia, metastatic disease, and osteomyelitis. These processes disrupt the endosteal surface, producing lytic areas, cortical thinning, and irregular margins that reflect rapid bone turnover or invasion.

This pattern helps distinguish from healing fractures, which typically show callus formation and remodeling rather than abrupt endosteal erosion. Benign bone cysts usually cause expansile, well-marginated areas with cortical thinning but not the aggressive endosteal destruction seen with malignant or infectious processes. Extraskeletal soft tissue invasion focuses on the soft tissue component rather than endosteal involvement, so it doesn’t center on the endosteal lysis pattern.