periostoma

per·i·os·te·o·ma

(per'ē-os'tē-ō'mă),
A neoplasm derived from the periosteum.

periostoma

(pĕr″ē-ŏs-tō′mă) [Gr. peri, around, + osteon, bone, + oma, tumor]
A bony neoplasm around a bone or arising from its membranous sheath.