Osteoid osteoma and osteoblastoma. Similar histologic lesions with different natural histories.

A study of 9 new cases of osteoid osteoma and 3 new cases of osteoblastoma demonstrated very similar histologic findings. Both lesions were extremely vascular and frequently showed areas with histologic features of an aneurysmal bone cyst. Differentiation between the 2 lesions often depended on their clinical features and radiographic appearances. A review of 851 osteoid osteomas and 181 osteoblastomas from the literature supported a difference, however, in the natural history of the 2 lesions with osteoid osteomas tending toward regression, and osteoblastomas tending toward progression and possible late malignant transformation. Osteoid osteomas were found to have a 4.5% recurrence rate compared with a 9.8% recurrence rate for osteoblastomas (p less than 0.01). No recurrence has ever been reported after complete en-bloc resection of either lesion and this must be considered the surgical treatment of choice for both lesions where possible. Despite apparent incomplete excisions, cures are achieved in many cases among both lesions.