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Musculoskeletal tumours can present diagnostic challenges

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Red flags you cannot miss.

Musculoskeletal tumours provide a very challenging group of clinical problems that require extensive clinical experience to treat. A thorough knowledge of a diagnostic and treatment algorithms are needed in their evaluation as well. Bone and soft tissue tumours present in many ways when located in the musculoskeletal system. This article will outline the challenges associated with the presentation of both entities.

Benign bone tumours often present in asymptomatic fashion. They are often found serendipitously after an injury or during a screening study in children. In this instance, as long as they are not painful, they are followed clinically. Typically, they will have very well-defined borders and a sclerotic rim. If there are any concerns about the aggressiveness of the lesion, short interval radiographic and clinical follow-up versus advanced imaging is indicated. Malignant bone tumours often cause pain and swelling. Sometimes after an injury, it can be difficult to determine whether radiographic imaging is warranted. The pain is associated with an injury should subside over a couple of days to a couple of weeks. If the pain does not subside plain radiographs of the affected bone should be obtained. Typical symptoms associated with aggressive/malignant bone tumours include night pain that awakens the patient from sleep, pain that is unrelieved by rest, and pain which is constant.

The presence of constant pain is more commonly a worrisome finding. Neoplastic soft tissue musculoskeletal pain is not often increased with activity and is not relieved by rest. Plain radiographs are the first imaging modality that should be obtained upon presentation for a bone lesion. Benign lesions often have a geographic pattern where all borders of the tumour are fully delineated on plain x-ray alone. Malignant tumours have destructive patterns of behaviour characterised by a moth-eaten pattern or permeative pattern of bone destruction.

Both of these patterns of bone destruction do not allow complete delineation of the borders of the tumour and necessitate further evaluation when present. If there any concerns on plain radiographs about the aggressiveness of the lesion, advanced imaging is required. MRI delineates the bone characteristics as well as the surrounding soft tissue characteristics better than CT scan and is the preferred imaging modality. When an MRI demonstrates aggressive findings, referral to a specialist in musculoskeletal tumours should occur.

Benign soft tissue masses are extremely common. Malignant soft tissue masses are outnumbered by benign masses by greater than 100-1. The exact incidence of benign soft tissue masses is unknown as many of these are asymptomatic and often undetected. The characteristics of benign soft tissue masses are size less than 4-5 cm, superficial to fascia, softer than muscle, and mobility when palpated. Benign soft tissue masses are painful much more frequently than malignant soft tissue masses. Post traumatic injuries can mimic soft tissue masses and need to be followed closely. Stability of size is also a characteristic of a benign soft tissue mass. Pain is a misconstrued characteristic of a soft tissue mass that is malignant. Malignant soft tissue masses most commonly present as a painless mass. The characteristics of malignant soft tissue masses are size greater than 5 cm, deep to fascia, firmer than muscle, fixed to fascia, and those that are rapidly growing. Malignant soft tissue masses in the extremities are most often soft tissue sarcomas. If the presence of any of the characteristics associated with malignant soft tissue masses are present, an MRI with and without contrast is indicated.

Heterogeneity of signal intensity on MRI is also concerning if the lesion is correlated with other findings for malignancy. If there are concerning findings on the MRI, referral to a specialist in musculoskeletal tumours is needed.

Once findings of a potentially aggressive soft tissue or a bone tumour are demonstrated, systemic staging is indicated. Malignant musculoskeletal tumours most commonly metastasize to the lungs and therefore a chest CT is warranted. A technetium whole-body bone scan is utilised for bone tumours to see if the lesion is isolated or multifocal. In patients over 40 years of age where metastatic disease is a concern and abdomen pelvis CT scan should be performed to evaluate for primary tumour sites. A PET-CT scan is also a potential option to evaluate the entire body for metabolically active areas. This test is more expensive and has a higher false-positive rate than CT and bone scan. Therefore, the clinical care team needs to evaluate the utilisation of a PET-CT carefully.

Systemic problems such as infection can mimic both bone lesions and soft tissue masses. Unexplained extremity pain that does not go away within a couple of weeks should have plain radiographs. Unless the bone and/or soft tissue lesion can be confirmed to be benign on plain x-ray or exam, advanced imaging is often required. Sometimes trauma can also mimic bone and soft tissue masses.

Myositis ossificans is a reactive, posttraumatic bone-forming lesion that demonstrates ossification in the soft tissues. Clinical correlation must be used with the appropriate imaging studies to confirm diagnosis. Biopsy of this lesion should be avoided if at all possible since the histology can be confused for a malignant lesion by an inexperienced pathologist.

Trauma can also cause bleeding into either cystic structures such as a Baker’s cyst or the creation of a hematoma. Sometimes advanced imaging can have a difficult time telling the difference between hemorrhagic changes and malignancy as they both can be heterogeneous in signal intensity on MRI. In this case, serial imaging done in short intervals and/or biopsy may be needed to rule out an aggressive lesion.

Musculoskeletal neoplasms are a challenging group of diagnoses for even experienced clinicians. Using the above-outlined algorithm, non-specialist physicians can appropriately evaluate these patients. Whenever the clinical and radiographic evaluation brings a concern for musculoskeletal malignancy, the patient should be referred to a musculoskeletal oncology expert with experience in management of these challenging problems.

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Dr Joel Mayerson

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