Osteoblastoma is a solitary, benign and self-limited tumor that produces
osteoid and bone. The tumor occurs in the dorsal aspect of vertebrae, the metaphysis or diaphysis of long bones, and
rarely in the pelvis.
In
the spine, the tumor is usually located in the posterior processes while the vertebral bodies are spared. The
differential diagnosis of osteoblastoma includes osteoid osteoma, osteosarcoma, giant cell tumor and aneurysmal bone
cyst.
The
common symptoms are pain of long duration, swelling and tenderness. Tumors of the spine can cause scoliosis and
neurological symptoms.
On
x-ray, osteoblastomas appear as a radio-lucent defect with a central density due to ossification. The lesion is well
circumscribed and may have a surrounding sclerosis. The tumor demonstrates increased isotope uptake on bone
scan.
On
gross examination, osteoblastomas are red to tan in color with hemorrhagic areas. The compact tissue is granular,
friable and gritty. Hyperemia is particularly evident in the spongy bone of vertebrae, ribs and the pelvis.
The
classic microscopic finding of osteoblastoma is irregular spicules of mineralized bone and eosinophilic osteoid
rimmed by osteoblasts. The vascular stroma is characterized by pleomorphic spindle cells. The tumor cells
differentiate into osteoblasts which make varying amounts of osteoid and woven bone. Cartilage production is a very
rare finding in an osteoblastoma and should raise the suspicion of osteosarcoma.
A biopsy is usually performed
to confirm the diagnosis. Surgical resection by curettage, intralesional excision or en-bloc excision are all
treatment options depending on the site. Cryosurgery, radiation and chemotherapy may have a role in aggressive and
surgically unresectable lesions of the spine.
Osteoblastoma
vs. Osteoid Osteoma
inconsistent pain vs.persistent, nocturnal pain irregular tissue pattern vs. regular
pattern >2 cm vs. < I cm
References
Bullough, Peter, Orthopaedic Pathologv (third edition), Times
Mirror International Publishers Limited: London, 1997.
Gitelis
S., R. Wilkins and EU Conrad, Benign Bone Tumors. Instructional Course Lectures, 45:425-46, 1991.
Huvos,
Andrew, Bone Tumors: Diagnosis. Treatment and Prognosis, W.B. Saunders Co., 1991.
Ruggieri,
P., RA McLeod, KK Unni and FH Sim, Osteoblastoma, Orthopedics, 19(7):621-4, July
1996.
Adapted, with permission from bonetumor.com By Henry DeGroot III, M.D.
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