An incisional biopsy was undertaken Peri operative
An incisional biopsy was undertaken. Peri-operative examination of the lesion revealed an expansile tumor mass brownish in color with focal whitish areas (Fig. 3). The lesion could be delineated from the surrounding cortical bone, and surrounding soft tissues. Histopathologically the biopsy material depicted a tumor composed of spicules of randomly arranged woven bones and are lined by a single layer of osteoblasts. The papain were two to three times larger than conventional osteoblasts, were epithelioid in morphology with large vesicular nuclei, prominent nucleoli and abundant eosinophilic cytoplasm (Fig. 4). The woven bones were focally mineralized. The stroma is rich in vascularity and scattered osteoclast-type multinucleated giant cells noted. A diagnosis of aggressive osteoblastoma was rendered after considering clinical, radiological and histological features of the tumor.
Discussion Osteoblastoma is a rare benign, bone-forming tumor, having similar clinical and histological features to those of osteoid osteoma . The tumor is more commonly occurring in males (2.5:1), among the teenagers and young adults . The present patient was a 2-year old male, which is not common age for occurrence of such tumor. Osteoblastoma is one of the rare neoplasms that predilects for the posterior elements of spine. In the appendicular long bones, the proximal femur, distal femur and proximal tibia are most commonly involved. Still less commonly the tumor may involves the tarsal bones (talus and calcaneous) . Patients with this tumor commonly presents with the insidious onset of a dull, aching pain which was noted in the present case. In contrast to the pain of osteoid osteoma, the pain of osteoblastoma may not always be nocturnal and is not relieved by salicylates [3,4]. Most osteoblastomas are in the range of 3–10cm while osteoid osteomas rarely exceed 1cm [3,4]. In the present tumor the mass was 3cm in the greatest dimension. Imaging studies reveals a characteristic oval to round, radiolucent lesion with scattered areas of mineralization having the central density of a trabecular bone and easily discernable margins. Mineralization varies from completely radiolucent to extensive. The present tumor had a well-defined margin and focal mineralization. Unlike osteoid osteoma, there is no surrounding dense cortical sclerosis . The size and extent of the tumor in the cortical bones best evaluated by CT, hence helps in preoperative evaluation and planning for surgery. The extent of the lesion within the medulla, soft tissue, areas of cystic degeneration and hemorrhage (which may occur in a few cases) can be best perceived on MRI study [2,5]. The radiographic appearance of aggressive osteoblastoma and conventional osteoblastoma is similar. Osteoblastoma may have radiological features mimicking to those of malignant bone tumor, such as cortical destruction and extraosseous soft tissue expansion . In the present case, cortical destruction was noted which radiologically mimicked an aggressive neoplasm. Khin et al.  reported one case of aggressive osteoblastoma in humerus where radiological features were mimicking osteosarcoma. Other radiological differential diagnoses are giant cell tumor and aneurysmal bone cyst . In 1972 Dorfman incorporated osteoblastoma in an article describing malignant transformation of benign bone lesions and noted four of 23 cases of osteoblastomas displayed recurrent behavior and histologic features. These cases would merit the title “aggressive osteoblastoma,” though characteristic histological features were not specified . Later, Dorfman and Weiss defined aggressive osteoblastoma as a borderline osteoblastic tumors in 1984 and proposed the presence of epithelioid osteoblasts was a characteristic histologic feature . Incidence and skeletal distribution of aggressive osteoblastoma are currently not appraised as the tumor is significantly rare .