Osteoblastoma



Osteoblastoma


G. Petur Nielsen, MD

Andrew E. Rosenberg, MD










Radiograph of humerus shows a lytic osteoblastoma of the mid shaft surrounded by solid periosteal new bone. It extends into periosseous soft tissues where cloud-like neoplastic ossification is noted.






A long bone with an osteoblastoma involves the cortex and surface of bone. The well-circumscribed tumor is oval and red with speckled tan-white foci, which correspond to areas rich in neoplastic bone.


TERMINOLOGY


Abbreviations



  • Osteoblastoma (OB)


Synonyms



  • Giant osteoid osteoma


Definitions



  • Benign bone-forming neoplasm composed of woven bone trabeculae lined by osteoblasts



    • Tumor > 2 cm in dimension


ETIOLOGY/PATHOGENESIS


Etiology



  • Cause unknown; not associated with any syndrome; no specific cytogenetic abnormality


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Uncommon; accounts for 1% of primary bone tumors



      • Responsible for 3% of primary benign bone tumors


  • Age



    • Diagnosed in adolescents and young adults (2nd-4th decade)



      • 75% younger than 25 years old at diagnosis


      • Mean age: 20 years


  • Gender



    • Males affected more frequently than females (2:1)


Site



  • Most commonly arise in tubular bones



    • Approximately 60% develop in appendicular skeleton



      • Frequently involve metadiaphyseal region of tubular bones


      • Centered in cortex and surface in 65% and located in medullary cavity in 35% of cases


      • 12% occur in femur; 10% originate in tibia; 9% involve bones of foot and ankle


  • Axial skeleton frequently affected



    • 30% arise in spinal column



      • Originate in posterior elements, especially lamina and pedicles; vertebral body involvement occurs secondarily


      • Cervical > lumbar > thoracic > sacral


  • Craniofacial bones involved in 10% of cases



    • Mandible most common location


Presentation



  • Pain, swelling, decreased range of motion


  • Tumors located in spine can cause neurological symptoms



    • Numbness, tingling, paraparesis, paraplegia


  • Small percentage associated with systemic “toxic” symptoms


Treatment



  • Curettage or selective en bloc resection


  • Radiation when located in inaccessible site


Prognosis



  • Curettage associated with local recurrence in approximately 20% of cases


  • Aggressive variant behaves similar to conventional type


  • Malignant transformation in osteoblastoma is exceptionally rare


IMAGE FINDINGS


Radiographic Findings



  • Expansile, well-defined, oval mixed lytic and blastic mass




    • Peripheral lucent halo surrounds central area of mineralization


    • Poorly defined margins in small minority


  • Periosteal reactive bone common; usually solid but may be laminated or spiculated


MR Findings



  • Well-delineated mass that is low to intermediate signal intensity on T1 and intermediate to high signal intensity on T2



    • Mineralized areas manifest as signal void (dark)


    • Tumor and edema enhance with contrast


CT Findings



  • Expansile lytic and sclerotic mass with circumscribed margins and surrounding reactive bone


Bone Scan



  • Intense uptake on scintography


MACROSCOPIC FEATURES


General Features



  • Solitary, well-circumscribed, tan-white, dark red, gritty



    • Rarely multifocal/multicentric


  • Cystic changes (aneurysmal bone cyst-like changes) prominent in 10% of cases


  • Delineated from soft tissues by periosteal shell of reactive bone


Size



  • Tumors range from 2-20 cm in dimension



    • Most tumors are 3-5 cm


MICROSCOPIC PATHOLOGY


Microscopic Features



  • Sharply demarcated


  • Neoplastic woven bone trabeculae deposited in haphazard, interconnecting, or sheet-like patterns



    • Bone rimmed by osteoblasts and scattered osteoclasts



      • Osteoblasts are ovoid or round, with moderate amounts of eosinophilic or purple cytoplasm, and eccentric nuclei with fine chromatin


  • Vascular connective tissue fills intertrabecular space


  • Scattered mitoses with no atypical forms


  • Necrosis usually absent or focal


  • Occasional cystic change mimicking aneurysmal bone cyst


  • Tumors composed of 75% epithelioid osteoblasts known as aggressive osteoblastoma



    • Epithelioid osteoblasts are large and polyhedral with abundant eosinophilic cytoplasm, vesicular nucleus, and prominent nucleolus


  • Cartilaginous variant (5%) contains well-formed hyaline cartilage


  • Pseudomalignant type contains osteoblasts with large, hyperchromatic, vacuolated nuclei that represent degenerative changes


DIFFERENTIAL DIAGNOSIS


Osteoid Osteoma



  • < 2 cm; characteristic clinical symptoms


Aneurysmal Bone Cyst



  • No haphazardly joining trabeculae of woven bone


Osteoblastoma-like Osteosarcoma



  • Grows with infiltrative pattern


DIAGNOSTIC CHECKLIST


Pathologic Interpretation Pearls



  • Tumor is well demarcated and neoplastic bone is rimmed by osteoblasts



SELECTED REFERENCES

1. Berry M et al: Osteoblastoma: a 30-year study of 99 cases. J Surg Oncol. 98(3):179-83, 2008






Image Gallery




Imaging Features






(Left) AP bone scan shows a small oval focus of intense isotope uptake on the left of T2. (Right) CT scan through osteoblastoma of pedicle and lamina of the vertebra demonstrates a well-circumscribed, expansile, oval mass, which contains substantial internal fine ossification. The tumor impinges upon the spinal canal. Thick periosteal reaction is present along the surface of the lamina and the base of the spinous process image.

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Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Osteoblastoma
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