In endosteal bone formation, how does slow-growing lesion appear compared with fast-growing lesion?

• A. Slow growing: Lamellar bone deposited on preexisting trabecular surfaces with thickened trabeculae; Fast growing: Woven bone deposited perpendicular to trabecular surfaces forming a web in intertrabecular space
• B. Slow growing: Woven bone deposited perpendicular to surfaces; Fast growing: Lamellar bone deposited on preexisting surfaces
• C. Slow growing: Periosteal reaction along cortex; Fast growing: No periosteal reaction
• D. Slow growing: No osteoblast activity; Fast growing: Abundant osteoclasts

Answer: (A)

Endosteal bone formation differs by how quickly a lesion grows. When growth is slow, the bone has time to lay down organized lamellar bone on preexisting trabecular surfaces, producing thickened, well-ordered trabeculae. This reflects gradual remodeling and maturation of bone along internal surfaces. In contrast, rapid lesion growth triggers a burst of osteoblastic activity that deposits woven bone in a disorganized fashion, filling intertrabecular spaces and often oriented perpendicular to the trabecular surfaces, forming a loose, web-like matrix. Woven bone is immature and rapidly produced, while lamellar bone is mature and orderly.

This matches the described pattern: slow-growing lesions yield lamellar bone on existing structures with thickened trabeculae, whereas fast-growing lesions create a woven, disorganized network bridging spaces.