An 11-year-old girl developed a rare type of benign bone tumor called BPOP (Bizarre parosteal osteochondromatous proliferation) on her wrist that unusually extended into the bone marrow. Doctors used imaging scans to diagnose the condition and surgically removed the tumor along with part of the bone. After surgery, the girl’s arm movement improved significantly, and one year later there were no signs the tumor had returned.