Findings: A frontal radiograph of the left distal femur demonstrates thick laminated periosteal reaction. No definite cortical destruction nor soft tissue mass is identified. Axial and sagittal T1 weighted images through the distal femur demonstrate a well-defined lesion just medial to the femur which demonstrates diffuse homogeneous enhancement. The cortex is intact without disruption.

Diagnosis: Soft tissue hemangioma.

Discussion: The finding of focal, thick periosteal reaction of the distal femoral metaphysis has several differential possibilities. These include a stress fracture, osteoid osteoma, infection as well as a parosteal osteosarcoma. There are several features which differentiate these etiologies. An osteoid osteoma contains a lucent nidus which may contain a central calcification. This would be well visualized on a CT scan and is more commonly cortically based. In addition, a clinical history of pain at night relieved by NSAIDS is typical. A stress fracture would be positive on all three phases of a triple phase bone scan. A parosteal osteosarcoma has the best prognosis of all osteosarcomas and is usually seen in a slightly older age group than the conventional osteosarcomas. The lesion is normally a dense mass attached to the cortical surface with central area of calcified matrix.

Reference:
Greenspan A. Orthopedic Radiology: A Practical Approach.
Lippincott, Williams & Wilkins; 2000:655-672, 550-557.

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