Lumbosacral aggressive osteoblastoma with extensive flare phenomenon: A diagnostic pitfall

While osteoblastoma is a rare benign bone-forming tumor, its aggressive variant can mimic malignant bone tumors. This resemblance is especially pronounced when accompanied by a flare phenomenon. We report a 12-year-old female with progressive neurological deficits and a lumbosacral mass. The initial MRI suggested a malignant bone tumor due to an ill-defined, avidly enhancing lesion at L4-S1 with severe canal stenosis. However, CT imaging revealed a more benign appearance, showing a well-defined lytic-sclerotic lesion with a narrow zone of transition. Histopathology confirmed the diagnosis of an aggressive osteoblastoma. This case highlights the importance of recognizing the flare phenomenon as a potential imaging pitfall in aggressive osteoblastoma, emphasizing the necessity of multimodal imaging-histopathology correlation for correct diagnosis and management.