[spoiler]In a case of osteosarcoma, when the lesion grows rapidly but steadily, the periosteum will not have enough time to lay down even a thin shell of bone, and the pattern may appear quite different. In such cases, the tiny fibers that connect the periosteum to the bone (Sharpey’s fibers) become stretched out perpendicular to the bone. When these fibers ossify, they produce a pattern sometimes called “sunburst” or “hair-on-end” periosteal reaction, depending of how much of the bone is involved by the process.
Learn More: Another pattern seen in rapidly growing processes is called the Codman’s triangle. This is a bit of a misnomer, since there really is not a complete triangle. When a process is growing too fast for the periosteum to respond with even thin shells of new bone, sometimes only the edges of the raised periosteum will ossify. When this little bit of ossification is seen tangentially on a radiograph, it forms a small angle with the surface of the bone, but not a complete triangle. So, when a process is growing too fast for even the Sharpey’s fibers to ossify, one may only see a soft tissue mass arising from the bone, perhaps with small Codman’s triangles at its margins. [/spoiler]