Fibrous cortical defect (Fig. 20.3). This most common abnormality has a characteristic oval X-ray appearance with a sharp margin and often multilocular. No specific treatment is required.

Fibrous dysplasia. This can present in mono- or polyostotic forms and is seen more commonly between the second and third decades. The radiographic appearance is of a ground-glass expansile lesion, often with a bowing of the affected bone. A ‘shepherd’s crook’ deformity is seen in the proximal femur as a result of this bowing and possible multiple fractures. The polyostotic form can be associated with hypothyroidism, vitamin D-resistant rickets and the Cushing syndrome. Albright’s syndrome includes the polyostotic dysplasia with café-au-lait spots and precocious puberty. The lesions are reasonably characteristic on X-ray but occasionally a biopsy is required. When painful, these are adequately treated with curettage and bone grafting. Occasionally there can be an associated fracture, although this is rare.

Simple bone cyst (Fig. 20.4). These cysts may occur during growth and are commonly located adjacent to the epiphyseal plate. They are usually asymptomatic until pathological fracture occurs. The radiographic appearances show a well defined radiolucent lesion, often with this pathological fracture.

Bone scans confirm a decreased uptake in the area and treatment is unnecessary unless there is a risk of fracture. These cysts can heal spontaneously after a fracture, but when in doubt aspiration and an injection of methylprednisolone acetate has an 80–90% success rate. Curettage and bone grafting is occasionally necessary.

Aneurysmal bone cyst (Fig. 20.5). These cystic cavities contain a thick brown-coloured membrane containing blood. They may occur in any bone, including the vertebrae. Approximately 50% are primary and 50% are the result of a benign lesion such as a chondroblastoma.

Radiographic signs confirm an expansile eccentric lesion and a thin ‘eggshell’ ring of bone. A CT scan may demonstrate a fluid level within the cyst. Treatment is usually by curettage andbone grafting.

Osteoid osteoma (Fig. 20.6 and Fig. 20.7). Any bone can be involved but more commonly the femur, tibia and vertebrae. There is a characteristic nidus in the cortical lesions, demonstrated on CT. Patients often have pain, which is particularly worse at night and can be relieved by aspirin. The natural history is thought to be self-limiting and resolution of symptoms has been described. Treatment has traditionally been surgical excision, although it is often difficult to localize the lesion. Guided laser ablation has shown encouraging results.

Ossifying fibroma. These are often considered to be a variation of fibrous dysplasia and are located eccentrically, either in the tibia or the fibula in young children. Occasional rapid expansion with or without a fracture is noted, but surgery is rarely indicated.

Enchondroma (Fig. 20.8). These benign tumours of mature hyaline cartilage are usually located centrally within the diaphysis of long bones and may represent the remnant of the epiphyseal plate. They can be solitary or multiple (Ollier’s disease) or associated with skin haemangiomas (Maffucci syndrome). Less frequently these lesions are located at the periosteum and are either juxtacortical or subperiosteal chondromas. These often involve the small tubular bones of the hand and feet and are noted more commonly in the second, third and fourth decades. Malignant transformation has been reported. Radiographic signs are characteristic, with an expansile nature of the bone, often with punctate calcification within. Treatment by curettage and bone grafting is occasionally required but patients should remain under review, especially with large tumours of the pelvis or spine.

Osteochondroma (Fig. 20.9). These are the most common benign bone tumours and probably represent a disorder of the normal enchondral bone growth. The appearance is either sessile or of a pedunculated lesion arising from the cortex of a long bone, adjacent to the physis (exostosis). Unlike a true neoplasm, the growth normally parallels that of skeletal maturity and is often noted during periods of rapid skeletal growth. Ninety per cent are single, but in 10% multiple osteochondromas occur. Most lesions are asymptomatic but can cause irritation of the surrounding structures (muscle, ligament). The clinical findings are usually of a palpable mass.

A cartilaginous cap of a few millimetres thickness usually covers the lesion. Large lesions can result in growth abnormalities (ulna bowing, etc.). Malignant transformation is possible and may occur in 10–25% of cases, although the exact incidence is unknown.

Chondroblastoma. This rare tumour occurs between 5 and 25 years of age, more commonly in the knee, hip and shoulder area. The tumour usually involves the physis and patients tend to present with pain. The lesion is lytic, with calcification occurring in approximately 50% of cases. Secondary aneurysmal bone cysts may occur. These chondroblastomas are aggressive, benign tumours but metastases can occur. In common with giant cell tumours, they should be regarded as potentially malignant.

Chondromyxoid fibroma. These occur eccentrically in the metaphysis of the proximal tibia commonly. Treatment includes curettage and bone grafting.

Giant cell tumour (Fig. 20.10). This occurs commonly in the third and fourth decade and more commonly around the knee or distal radius. The radiographic features are of an expansile lesion, which often lies eccentrically. The border is well defined with some sclerosis and is often juxtaposed to the articular cartilage. Pathological fracture is common and treatment includes surgical removal with curettage and bone grafting, with or without phenol ablation, cryosurgery or instillation of methylmethacrylate.

Malignant fibrous hystiocytoma (MFH) is a high grade tumour seen in adulthood. It commonly occurs around the metaphysis, in particular of the knee. Radiographs show a ‘moth-eaten’ osteolytic lesion with extensive cortical disruption but a minimal periosteal reaction and very little, if any, new bone formation. The underlying cell of origin is doubtful and treatment is difficult. The prognosis is unfavourable.

Osteogenic sarcoma (Fig. 20.11 and Fig. 20.12). These are the most common primary bone tumours and occur more commonly in children and young adults (Fig. 20.11). The tumour often presents as a swelling with a history of minimal trauma. The tumours are classified as primary or secondary (following Paget’s disease, X-ray therapy). The primary tumours are further classified according to their position (parosteal, central or multicentric).

Approximately 70% of patients present without a detectable metastasis, but in the 30% that do there is a high percentage of relapse following chemotherapy and local surgery. Limb sparing resection is possible with adjuvant chemotherapy. The prognosis for all types is poor.

Radiographic signs confirm the lytic lesion, elevation of the periosteum and the production of a ‘Codman’s triangle’.

Chondrosarcomas. These may be classified as central or peripheral, or primary versus secondary (secondary to a pre-existing lesion such as an osteochondroma). Patients usually present with a long history of pain, mass or both. These tumours are further differentiated into low, intermediate or high grade lesions. The behaviour of the tumour is related to the aggressive portion of the lesion and the prognosis is poor.

Ewing’s sarcoma (Fig. 20.13 and Fig. 20.14). This rare tumour occurs in the first and second decade of life and the small, primitive, round cells have a common karyotypic translocation between chromosome 11 and 22. Previously these were uniformly fatal, but major advances in treatment have been made with the use of chemotherapy and adequate local control. The most important adverse prognostic feature is metastatic disease detectable at the time of diagnosis. The 5-year relapse-free survival rate is 20% for those with metastatic disease, compared with 55% for those without metastases at the time of presentation.

Surgical resection is considered the optimal method of obtaining local control. The radiographic appearances include bone destruction with an ‘onion skin’ reaction of the periosteum. It may involve large areas of the diathesis and may appear to skip areas of the bone.

Synovial sarcoma. This tumour has histological similarities with the synovium of joint but rarely arises directly from the joint. They are often of a high grade histological appearance but may be well circumscribed or multinodular. Soft tissue calcification occurs in approximately 25% of cases and lymphatic and vascular metastatic spread is common, with a poor long-term prognosis.

Treatment depends upon the tumour but may involve radiotherapy, chemotherapy or hormone therapy. If pathological fracture occurs, intramedullary nailing is indicated. It is wise to nail the bone prophylactically in those lesions that involve more than 50% of the circumference of the bone to avoid an impending fracture.

An MRI scan of the bone can delineate the extent of the secondary deposit.