Presentation
Pain in the right lower thigh for 6 months. Pain is worse with activity and relieved by rest and simple analgesics. No history of trauma.
Patient Data
A faint focal radiolucent lesion with mildly sclerotic margins and narrow zone of transition is seen in the medullary cavity of the distal metaphysis of the right femur. No cortical breach, bone fracture, periosteal reaction, or associated soft tissue abnormality is seen. Overall radiological features are suggestive of a non-aggressive osseous lesion.
The subtle radiolucent lesion in the distal right femur has increased in size. Now it has ill-defined margins / wide zone of transition and associated periosteal reaction. Mild local soft tissue swelling is also appreciable. All these radiological features are worrisome for an aggressive/malignant osseous lesion which need further evaluation with MRI.
An osteolytic lesion is seen in the distal metaphysis (with mild diaphyseal extension) of the right femur. The lesion shows mixed signal intensities on T1 and T2 weighted images and has multiloculated cystic appearance on T2 weighted images. Multiple foci of hemorrhage are seen within the lesion. It has well-defined superior and inferior margins (narrow zone of transition); however, there is irregular endosteal thinning along the anterior and posterior margins of the lesion. Periosteal reaction and small extra-osseous soft tissue component are also appreciable along the anterior and posterior margins of the lesion. The lesion shows mild diffusion restriction. Post-contrast study shows enhancement at the superior and inferior aspects of the lesion as well as in the adjacent bone. Adjacent right knee joint appears unremarkable. No skip lesion is seen in the visualized portion of the right femur. These MRI features are suggestive of a primary malignant bone neoplasm.
Case Discussion
Unfortunately, the subtle abnormality was not identified by the reporting radiologist at initial presentation. Patient presented 5 months later with worsening pain and feeling of a lump in the right distal thigh. Repeat femur radiographs were performed, which demonstrated interval progression and an MRI was subsequently performed.
The lesion was resected and diagnosed as telangiectatic osteosarcoma of the right distal femur.
Differential diagnosis includes aneurysmal bone cyst, giant cell tumor of the bone, and rarely metastasis.