Osteoblastoma

Diagnosis

Osteoblastoma

History

Pain and swelling of the groin in a 37 year-old male

Findings

@1.87 Axial CT scan of the right  ilio pubic branch with a large tumoral mass at the expense of bone. This well limited mass sclerotic margin on the osseous side and peripheral cortical which disappeared. Calcification was visualized in its middle.

@8.12 Sagittal and @3.12, @4.10 coronal T2 sequence showing the high signal of edema around the tumor

DDx

The feature of cortical expansion may make osteoblastomas appear similar to an aneurysmal bone cyst or giant cell tumor; however, no central calcification should be found within the latter tumors.

“Aggressive osteoblastoma” has similarities to osteosarcoma, radiographically demonstrating cortical destruction and a more prominent periosteal reaction with occasional soft-tissue extension, hence the distinction must be based on histological examination.

Discussion

DEFINITION

Osteoblastoma is a rare bone tumor affecting the long bones and posterior elements of the spine, and accounts for 1% of primary bone tumors.

Osteoblastoma in the region of the hip is exceedingly rare, accounting for 3–8.8% of all osteoblastomas.

Osteoblastoma is considered as a benign tumor with an histologic pattern similar to that of osteoid osteoma.

It differs from osteoid osteoma predominantly by its size, osteoblastoma being greater than 0.5 cm in diameter.

Osteoblastomas are considered to be benign; they consist predominantly of osteoid tissue and spicules of bone within a hypervascular stroma.

The osteoid tissue is surrounded principally by osteoblasts and occasional fibroblasts.

CHARACTERISTIC CLINICAL FEATURES AND RADIOLOGIC FINDINGS

Radiographically, most tumors are within an intact cortex, usually expanded and thinned, with prominent periosteal new bone formation and various degrees of internal ossification.

Computed tomography clearly demonstrates the central calcification within lesion (typical finding for osteoblastoma), and delineates the cortical destruction or soft-tissue extension.

Using MRI, “flare phenomenon”has been reported, which is a widespread inflammatory response surrounding an osteoblastoma that leads to diffuse, reactive inflammatory infiltration.

References

1. Osteoblastoma in the region of the hip.Yang CY, Chen CF, Chen WM, Wu PK, Lee FT, Chen PC, Liu CL, Chen TH.J Chin Med Assoc. 2013 Feb;76(2):115-20. doi: 10.1016/j.jcma.2011.10.014.
2. Pitfalls in diagnostics of hip pain: osteoid osteoma and osteoblastoma.von Chamier G, Holl-Wieden A, Stenzel M, Raab P, Darge K, Girschick HJ, Beer M.Rheumatol Int. 2010 Jan;30(3):395-400. doi: 10.1007/s00296-009-0943-2. Epub 2009 May 15.