Age / Sex : 15 / M

Chief complaint : left thigh pain for 2 months

Discussion

Answer:  Osteoblastoma

Findings:

1. Radiograph

Irregular-shaped cortical osteolytic lesion surrounded by thick sclerosis and continuous periosteal reaction at diaphysis of femurt.  

2. MRI

Intracortical enhancing lesion with adjacent cortical thickening and T2-hyperintense periosteal new bone formation. There is a tiny dark-signal intensity spot inside the enhancing lesion, suggestive of mineralization. Reactive bone marrow edema is observed in the adjacent femoral shaft.

Differential Diagnosis:

1. Osteoid osteoma


2. Intracortical abscess

Discussion:

 - Osteoblastoma most often occurs within the posterior elements of the vertebral

column, but also involves the long tubular bones in approximately one-third of cases, the proximal femur being the most frequent site of involvement. The lesion may be medullary, intracortical, or periosteal (juxtacortical) in location.

- Imaging finding: variable

• In the long bones, it typically presents as a well-defined, round-to-ovoid, predominantly lytic lesion, with areas of central calcification or ossification and variable degrees of reactive sclerosis, cortical thickening and benign periosteal new bone formation


• usually of intermediate size, ranging from 2 cm to 6 cm, and may cause bone expansion


• in long tubular bones, diaphysis or metadiaphysis. Eccentric 46%, cortically-based 42%


• on T1WI MRI: low to intermediate signal. Lower signal foci if matrix present.


• On fluid-sensitive sequences: low~high SI with variable degrees of inhomogeneity


• Enhancement: mild to intense. May have extensive peripheral marrow edema and associated soft tissue edema (flare phenomenon).

References:

1. Diagnostic imaging: Musculoskeletal: Non-traumatic disease, 2^nd edition. Elsevier. pp.208-210.


2. Periosteal osteoblastoma: report of a case with a rare histopathologic presentation and review of the literature. Mortazavi et al. Skeletal Radiol 2007;36:259-264