Osteoblastoma

Contents

Introduction

Osteoblastoma is sometimes called "giant osteoid osteoma" because it is histologically identical to osteoid osteoma, but larger. Osteoblastoma is less common than osteoid osteoma, accounting for less than 1% of the primary bone tumors.

Clinical Findings

Approximately 30-40% of osteoblastomas are found in the spine, where they most often affect the posterior elements, including spinous and tranverse processes, lamina, and pedicles. All areas of the spine may be involved, from the upper cervical region to the sacrum. The diaphysis of long bones, particularly the femur and tibia, is also a common site. Spinal involvement may present with myelopathic or radicular symptoms, progressive painful scoliosis, or torticollis if the lesion is in cervical spine. In nonvertebral locations, pain is usually the prominent complaint. The pain is less localized than the pain of osteoid osteomas and much less likely to be relieved by salicylates.

Osteoblastomas are tender, and direct palpation often localizes a lesion, even when it cannot be seen on a plain radiograph.

Radiographic and Histologic Features

Table 1 presents the typical radiographic and histologic features of osteoblastoma while comparing it to features of osteoid osteoma. Hosalkar et al have reported (Clin Orthop Relat Res. 2005 Jul;(436):286) that CT imaging is more diagnostically accurate in suspected cases of osteoid osteoma as MRI tends to present a more aggressive picture and can lead to diagnostic inaccuracy.

Table 1. Typical radiographic and histologic features of osteoid osteoma as compared to an osteoblastoma.

Features	Osteoid osteoma	Osteoblastoma
Histologic Features
Gross (Macroscopic)	Round or oval, reddish-brown, most ?1 cm diameter	Similar, but larger than osteoid osteoma (most 2-6 cm)
Histologic (Microscopic)	Distinct demarcation between nidus and surrounding reactive bone Interlacing network of immature bone and bony trabeculae, with focal areas of osteoblastic and osteoclastic activity	Demarcation is not significant Interlacing woven bone lined by osteoblasts within a fibrovascular stroma
Radiographic Features
Plain radiographs	Long bone; metaphysic or diaphysis Spine; posterior elements Small (? 1 cm), round-elliptical, lucent, intracortical (mostly) lesion surrounded by extensive reactive sclerotic bone	Spine; posterior elements Long bone; metaphysis or diaphysis 2-6 cm, round-elliptical lytic lesion surrounded by moderate reactive sclerotic bone
Computed tomography	Thin (1-2 mm) sections; provides exact localization of the nidus	Expansion of the involved bone with intralesional stippled ossifications

Fig. 1. Typical location in the posterior elements of the spine. Radiodense, expansile, bone producing neoplasm.

Fig. 2. Radiodense bone producing tumor. DDx Osteosarcoma (classic, parosteal), osteoblastoma, osteoma.

Fig. 3. Typical gross appearance, dense cancellous cortical bone.

Treatment

Osteoblastoma is a benign, but locally aggressive lesion. The tumor should be excised surgically, otherwise it continues to enlarge and damage the bone and adjacent structures.

Intralesional extended curettage is the preferred treatment for most lesions. As much of the surrounding bone should be removed as possible. Most osteoblastomas are controlled by extended curettage, but recurrence is not uncommon (approximately 10 to 20%).
En bloc excision may be preferred for lesions in expandable bones (e.g., fibula), aggressive-appearing lesions, and some vertebral lesions.

Reconstruction of the defect formed by excision depends on the site, but most defects require bone grafting.
For extremity lesions, extended period of protection may be needed.

Osteoblastomas located in sites inaccessible to surgical excision have been reported to respond to radiation therapy or chemotherapy.

Figures


Figure 1a. Typical location in the posterior elements of the spine. Radiodense, expansile, bone producing neoplasm.	Figure 1b. Typical location in the posterior elements of the spine. Radiodense, expansile, bone producing neoplasm.	Figure 2a. Radiodense bone producing tumor. DDx Osteosarcoma (classic, parosteal), osteoblastoma, osteoma.	Figure 2b. Radiodense bone producing tumor. DDx Osteosarcoma (classic, parosteal), osteoblastoma, osteoma.

Figure 3. Typical gross appearance, dense cancellous cortical bone.