Musculoskeletal primary tumours: treatment evaluation and detection of recurrences.

The role of imaging in treatment evaluation and detection of recurrences of musculoskeletal primary tumours is discussed.

Introduction

Neoadjuvant chemotherapy is increasingly used for musculoskeletal sarcomas[. Its effectiveness is evaluated histologically on the specimen. The result comes late, and is relevant for a very limited part of the remaining lesion. An earlier imaging result would be useful, as it would allow treatment to be adapted earlier. In soft tissue sarcomas, as the initial diagnosis and treatment are often inadequate, recurrences are very frequent; early detection is therefore desirable.

Treatment evaluation

Bone tumours

In osteosarcomas, on plain films or computed tomography (CT), a better limitation of a more ossified tumour usually indicates good responders. But there are too many mistakes. Size is not reliable, as an increase may be secondary to bleeding. On plain magnetic resonance (MR), remaining, or, even worse, increasing oedema around the tumour on T2-weighted images is a reliable indicator of non-response, without giving the exact location of viable tumour. Dynamic MR studies depict viable tumour exactly[. They require a fast acquisition (less than 2 min), repeated usually at 5–8 min, and postprocessing (subtraction, or functional display of the results on the whole image). Fat presaturation displays the results directly, and can be used, if robust enough. The exact value of positron emission tomography (PET) is still under investigation.

The results are not as reliable in Ewing tumours, as isolated tumour nests may remain that are too small to detect[.

Soft tissue sarcomas

Neoadjuvant chemotherapy is increasingly used[ to prevent metastases, and make surgery easier and less aggressive. Injected sequences are again the most reliable, especially dynamic ones. If isolated limb perfusion is used, dynamic MR is performed to plan the best surgical schedule[. Injected sonography with microbubbles is also promising in the soft tissues.

Detection of recurrences

Tumour recurrence is only detected on plain films if ossified. Metallic prostheses create artefacts on CT. If they are made of titanium, a very frequent situation, they allow an accurate MR examination. Gradient echo (GE) sequences and fat presaturation should be avoided in these cases.

An easy-to-follow algorithm should be used to detect local recurrences on MR; these occur all too frequently[. T2-weighted acquisitions should be performed first. If the whole lesion appears black, it is composed of scar tissue only, and the examination can be stopped. If there is a diffuse high signal without a mass following radiation therapy, it indicates only inflammatory treatment-induced changes. A high signal intensity mass justifies injecting contrast medium to differentiate a recurrence from haematoma or hygroma. Then it is wiser to use dynamic studies to better characterize the rare inflammatory pseudomasses and their late enhancement.