Osteosarcoma - distal femur

Case contributed by Dr Ali Abougazia

Presentation

Right lower thigh pain for a few months

Patient Data

Age: 16 years
Gender: Female
X-ray

A right femoral distal metaphyseal osseous lytic lesion is seen with wide zone of transition and aggressive pattern of bone destruction (permeative), aggressive periosteal reaction (Codman triangle) as well as osseous matrix and evidence of extraosseous soft tissue component.

Annotated image

These minute elongated holes within the cortical bone represent permeative pattern of bone destruction, caused by growth of the lesion through the Haversian channels of bone, and is a feature of highly aggressive lesions (compare with the normal cortex on the medial side of the femur).

MRI

A right lower femoral shaft metadiaphyseal osteolytic exophytic lesion is seen showing a wide zone of transition with the adjacent normal bone marrow and encasing the posterolateral circumference of the distal femoral shaft. The lesion elicits inhomogenous isointense T1 / T2 and high STIR signals with internal break-down foci of fluid signal. The lesion causes cortical destruction with and extraosseous eccentric soft tissue component measuring 9.1 x 8 x 7.7 cm in orthogonal dimensions. The lesion and the soft tissue component show heterogeneous contrast enhancement.

The quadriceps femoris muscle (mainly the vastus lateralis muscle) shows signal changes and post-contrast enhancement similar to the lesion and appears stretched over the lesion.

No other lesions in the scanned bones or invasion of the popliteal neurovascular bundle.

Case Discussion

The highly aggressive nature, the location and the age group of the patient narrow the differential diagnosis of this lesion to either osteosarcoma or Ewing sarcoma, however the osseous matrix in the lesion and the age of the patient (older than 10 years) as well as the eccenteric metaphyseal location favor osteosarcoma.

Osteosarcoma is a malignant bone forming tumor and the second most common primary bone tumor after multiple myeloma. It accounts for about 20% of all primary bone tumors. Its primary form occurs in young patients (10-20 years). Its secondary form occurs in the elderly, usually secondary to malignant degeneration of Paget disease, extensive bone infarcts or post radiotherapy. Patients usually present with bone pain, occasionally accompanied by a soft-tissue mass or swelling. They typically occur at the metadiaphysis of tubular bones in the appendicular skeleton. Commonest site is around the knee.

Ewing sarcoma is the second most common primary bone tumor of childhood after osteosarcoma. Typically occurs in children (especially before 10 years old), and has a slight male predilection. Presentation is non-specific with local pain being by far the most common symptom. As far as location within long bones, the tumor is almost always metadiaphyseal or diaphyseal. Commonest site is around the knee.

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