osteoid osteoma
A small, benign, bone-forming neoplasm that can arise from any bone but more frequently affects the long bones. The central portion of the neoplasm (nidus) contains differentiated osteoblasts which produce osteoid and sometimes bone. The lesion is usually surrounded by hypervascular sclerotic bone and has limited growth potential. Clinical signs and symptoms include pain and localized tenderness, at the site of the lesion. The pain may be intense but in the majority of cases it is completely alleviated by non-steroidal anti-inflammatory drugs. Prognosis is excellent and recurrences are rare.