Osteoid osteoma - femoral neck

Case contributed by Ammar Haouimi
Diagnosis almost certain


Persistent pain of the right hip with limited range of motion. No fever.

Patient Data

Age: 5 years
Gender: Male

The MRI images show an intracapsular well-circumscribed lesion of the femoral neck of intermediate signal intensity on T1WI, and T2WI with a peripheral hypointense rim on T1WI. The periphery of the nidus enhances more intensely than the central portion due to the presence of the unmineralized stroma. Associated reactive soft tissue and bone marrow edema are noted as well as an intense synovial enhancement with joint effusion.

The nidus, as well as the central mineralization, are better demonstrated on CT than on MRI. The nidus appears as a well-circumscribed osteolytic lesion of the femoral neck with minimal peripheral reactive sclerosis, marked medial cortical thinning, and central foci of calcification (central mineralization).

Case Discussion

CT and MRI features are highly suggestive of an intracapsular osteoid osteoma. Soft tissue and bone marrow edema, as well as joint effusion and synovial enhancement (synovitis), are well-visualized on MRI than CT.

Intraarticular osteoid osteoma, within or near a joint, is considered as a  separate clinical entity. The hip is considered the most commonly involved joint. With intraarticular osteoid osteoma, the reactive cortical sclerosis is minimal or absent (as in our case) due to a lack of cambium from the joint capsule (usually responsible for bone formation).

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