Osteosarcoma - distal femur

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  malignant bone forming tumour and the second most common primary bone tumour aftermultiple myeloma. It accounts accounts for about 20 20% of all primary bone tumours. 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 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 tumour 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.

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

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 postero-lateralposterolateral 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 extra-osseousextraosseous eccentric soft tissue component measuring 9.1 Xx 8 Xx 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 muclemuscle) shows signal changes and post post-contrast enhancement similar to similar to the lesion and and and appears stretched over the lesion.

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