Osteosarcoma imaging and differential diagnosis

Some patients experience pain in the lower part of the right thigh without obvious causes. The pain is persistent and does not ease after rest. Initially, they do not take it seriously or treat it. After the onset of the disease, they go to the hospital for treatment and are diagnosed with "osteosarcoma" through X-rays. In this case, what are the imaging diagnosis and differential diagnosis of osteosarcoma? Let's learn about it together.

Plain X-rays

X-ray films are the initial screening method for lesions, and the main manifestations are irregular bone destruction and bone hyperplasia in the bone marrow cavity, bone cortical destruction, different forms of periosteal hyperplasia and re-destruction of periosteal new bone, soft tissue masses and tumor bone formation therein. The diagnosis is mainly based on tumor bones, which generally appear as cloud-like, needle-like and plaque-like dense shadows. These tumor bones are immature bone tissues, which are directly formed by tumors and have no normal trabeculae. Most osteosarcomas can be qualitatively diagnosed by plain films, but the limitation is that the display of tiny bone destruction and soft tissue masses is unsatisfactory.

CT

CT examination is mainly used to detect suspicious bone destruction and tumor bone in plain film examination, and plays an important supplementary role to plain film. The bone destruction of osteosarcoma is mainly osteolytic, and CT shows patchy defects in cancellous bone, erosion of the inner surface of the bone cortex, or worm-eaten, patchy destruction of the entire layer of the bone cortex, or even large defects. Bone hyperplasia is manifested as irregular patchy high-density shadows in the cancellous bone and thickening of the bone cortex.

MRI

MRI is an essential examination method for staging osteosarcoma and is often used as the main means to evaluate the efficacy of neoadjuvant chemotherapy. When the bone marrow is infiltrated by tumor, even if it is very slight, it can show abnormal signals.

Diagnosis and differential diagnosis

Atypical osteosarcoma is easily misdiagnosed as chronic osteomyelitis or myositis ossificans. Osteomyelitis usually presents with acute onset, extensive lesions, and can spread to the entire bone. It is mainly characterized by periosteal hyperplasia. The degree of periosteal reaction is consistent with the degree of bone destruction and hyperplasia. There is no tumor bone formation or soft tissue mass. Myositis ossificans generally has a history of trauma.

Osteosarcoma has a clear age of onset and site of invasion, and its imaging manifestations are also characteristic. X-ray films showing typical osteosarcoma can confirm the diagnosis, but it cannot determine the extent of bone marrow invasion, let alone detect skipping sub-foci in the bone marrow, and it also has great limitations in accurately determining the extent of soft tissue invasion. Therefore, it is advisable to further perform MRI examinations on the basis of X-ray films to provide more direct and accurate information for treatment. The final diagnosis of osteosarcoma must be combined with pathology, imaging, and clinical comprehensive diagnosis, and none of the three can be missing.