Osteoblastoma

Osteoblastoma is a rare, benign primary bone tumor that arises from osteoblasts and produces osteoid and woven bone. Most commonly it measures larger than 2 cm in greatest dimension and can exhibit locally aggressive growth. It typically affects adolescents and young adults, with a male predominance. The spine, especially the posterior elements, is the most frequent site, followed by long bones such as the femur and tibia. Patients usually report dull, progressive bone pain and focal tenderness; spinal involvement may cause deformity or neurological symptoms due to canal compromise. Pain can be persistent and is not as consistently relieved by nonsteroidal anti-inflammatory drugs as seen with osteoid osteoma.

Imaging features include lytic, expansile lesions with cortical thinning and a variable sclerosis border. The lesion may contain internal calcifications and a lobulated appearance. CT provides detailed assessment of the bony architecture and matrix, while MRI evaluates soft-tissue extension and spinal canal involvement. Radiographic and histologic diagnosis should be correlated to distinguish osteoblastoma from more aggressive lesions.

Histologically, osteoblastoma shows abundant osteoid and woven bone produced by proliferating osteoblasts in a richly vascular stroma. Cells display benign cytology, with peripheral osteoblastic rimming; mitotic figures are uncommon. A subset is termed aggressive osteoblastoma when it shows more infiltrative growth and higher recurrence risk, though metastasis is rare.

Treatment is primarily surgical. Curettage with or without adjuvants or en bloc resection is chosen based on location and extent; spinal tumors may require stabilization. Radiation therapy is generally avoided due to potential malignant transformation. Prognosis is favorable after complete excision, but recurrence occurs in a notable minority, especially for aggressive forms.