20 Tumours of the musculoskeletal system and pathological fractures

Essential facts

1. A soft-tissue lump is likely to be sarcoma if it is painful, growing rapidly, larger than 5 cm in size and deep to deep fascia.

2. Metastatic bone tumours occur at any age, but are the most frequent cause of a painful lytic bony lesion in the elderly. Sclerotic lesions occur in prostate and breast cancer.

3. Pathological fractures occur after minimal force; they include osteoporotic fractures in the elderly, osteogenesis imperfecta in the young, fractures through infected or dead bone, and fractures through neoplastic bony lesions.

4. The matrix of a benign cystic lesion is purely lytic, and the margins are well defined; malignant lesions and rapidly growing benign lesions have infiltrative edges.

5. Avoid fixation of a pathological fracture before obtaining a definitive diagnosis.

6. Most malignant pathological fractures will not heal; therefore, the implant should be ‘load-bearing’ rather than ‘load-sharing’.

7. Malignant bone tumours are best managed within a multidisciplinary team.

Tumours

The word tumour comes from the Greek word for ‘swelling’. Swellings of the musculoskeletal system can be classified as neoplastic (benign), neoplastic (malignant), inflammatory or miscellaneous. In general, the lay-person’s term for neoplasm is tumour. A neoplasm is an abnormal growth of cells over which control of growth has been lost. Removal of the stimulus that caused it does not stop it growing, and the tissue is clonal (has arisen from a clone – an almost identical mother cell).

Neoplastic (benign)

Benign neoplasms do not metastasize to other tissues beyond the local tumour. Sometimes the tumour may become malignant, but only if the classification of the tumour changes (for example, an enchondroma to a chondrosarcoma). A soft-tissue swelling that is pain-free, static or slowly growing, superficial and less than 5 cm in size has only a tiny chance of being malignant.

Important benign neoplasms of soft tissue are listed in Table 20.1; they are far more common than malignant ones.

Table 20.1 Benign neoplasms of soft tissue

Tumour	Features
Lipoma	Very common. MRI features usually typical fat but may be difficult to discriminate atypical lipoma from low-grade liposarcoma
Aggressive fibromatosis (desmoid tumour)	Locally difficult to resect completely. Resolution over many years. Radiotherapy, tamoxifen, vitamin C may help
Myxoma	Difficult to resect locally and may recur after many years. Occasionally de-differentiates to myxoid sarcoma
Leiomyoma	In retroperitoneum and gastrointestinal tract may have malignant potential
Haemangioma	May be congenital or acquired. Large ones in children may require multidisciplinary approach because of skin involvement
Schwannoma	Usually benign on a major nerve. Can be ‘shelled’ away from the nerve without damage
Neurofibroma	Integral within the nerve and cannot easily be ‘shelled’ away from it
Synovial chondromatosis	Forms in large joints and is difficult to eradicate. May de-differentiate to chondrosarcoma
Giant cell tumour of tendon sheath	Forms on tendons and easily ‘shells’ away from them

Benign tumours of bone usually grow slowly and, therefore, tend to have a well defined margin. The bone has chance to react and often does so by expansion with cortical changes. Treatment is frequently a biopsy-cum-curettage to remove the majority of macroscopic tumour without causing morbidity. In most benign bone tumours, this allows bone healing to eradicate remaining microscopic tumour. Important examples of benign bone neoplasms are listed in Table 20.2.

Table 20.2 Benign neoplasms of bone

Tumour	Radiographic Features	Clinical Features/Treatment
Simple (unicameral) bone cyst	Large, expanded, well demarcated, lytic metaphyseal lesion	Children. Heals spontaneously after fracture or may require bone graft
Aneurysmal bone cyst	Large lytic metaphyseal lesion	Blood-filled spaces. Curettage necessary
Giant cell tumour of bone	Metaphyseal to articular surface. Aggressive appearance	Solid tumour with soft-tissue involvement. Bony destruction results in extended joint replacement surgery
Eosinophilic granuloma (Langerhans’ cell disease)	May have aggressive appearance	Part of a systemic disorder of histiocytes. Check anterior pituitary function
Osteoid osteoma	Cortical lesion. Central nidus with lytic ring and surrounding sclerosis	Children and young adults. Osteoid-producing tumour. Painful. May be curetted or ablated using heat under CT control
Osteoblastoma	Large lytic metaphyseal lesion	Similar to osteoid osteoma over 2 cm in size
Chondroblastoma	Epiphyseal	Curettage and bone grafting
Fibrous cortical defect	Bubbly, lytic within cortex. Little change with time	Curettage if large and painful

Neoplastic (malignant)

Malignant neoplasms can metastasize to distant organs. They have invasive qualities both locally and distantly. It is this feature that makes the tumour so difficult to treat and may lead to the patient’s death. Malignant tumours of the musculoskeletal system can be divided into tumours of bone or soft tissue. Primary bone tumours are usually sarcomas. Sarcomas have cells of origin that reflect the range of mesodermal tissue from which they arise (soft tissue – liposarcoma, fibrosarcoma, rhabdomyosarcoma, leiomyosarcoma, angiosarcoma, haemangiosarcoma, synovial sarcoma, malignant peripheral nerve sheath tumour; bony – osteosarcoma, chondrosarcoma, Ewing’s sarcoma). Most soft-tissue sarcomas behave in a similar way independent of subtype.

Most soft-tissue sarcomas are graded according to their mitotic rate. Low-grade sarcomas have a slow growth rate and low metastatic potential. All cancers have the potential to spread locally, to regional lymph nodes, and distantly. Sarcomas rarely spread to lymph nodes, so the main distant site for metastasis is the lung. This is most frequent in high-grade sarcomas.

A patient who presents with a soft-tissue lump has a high (>90%) risk of this being a sarcoma if it is: (a) painful, (b) growing rapidly, (c) larger than 5 cm in size and (d) deep to deep fascia. Figure 20.1 shows a magnetic resonance imaging (MRI) scan of a large soft-tissue sarcoma demonstrating most of these features. An X-ray may provide evidence of calcification (calcified haematoma, possibly synovial sarcoma). MRI defines solid from cystic and identifies a solid focus for biopsy, which should be undertaken only by the surgical team that will undertake the definitive surgery, or a competent radiologist. Nowadays these multidisciplinary teams exist in teaching hospitals accredited as regional or national centres for sarcoma care. The histopathologist should identify the lesion through haematoxylin and eosin staining and immunohistochemistry to subtype the biopsy specimen. Cytogenetics may be useful. It should be remembered that the biopsy may not be representative of the entire specimen. Following a diagnosis of sarcoma, further ‘staging’ investigations would include blood tests (full blood count, clinical chemistry, clotting screen, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP)) and computed tomography (CT) of the chest to identify any lung metastases.