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  • Introduction Benign tumours of the bone

    2019-06-24

    Introduction Benign tumours of the bone consist of a wide variety of different neoplasms. These tumours vary in terms of incidence, clinical presentation and require a diverse array of therapeutic options. The incidence of benign bone tumours is debated due to their often asymptomatic presentation and difficulty in detection [1]. Overall, 8 different types can be distinguished; osteochondroma, osteoma, osteoid osteoma, osteoblastoma, giant cell tumour, aneurysmal bone cyst, fibrous dysplasia and enchondroma. These tumours can be roughly divided into categories based on their cell type: bone-forming, cartilage-forming, as well as AT7867 and vascular [2]. Some other forms of benign tumours may also present, however due to their low incidence they will not be discussed. We will discuss the most common first followed by descending prevalence.
    Osteochondroma These cartilaginous tumours represent most of the benign bone tumours (approx. 30%). Most commonly found in the femur and tibia, osteochondroma occur mainly in the metaphysis and diametaphysis and projects out of the underlying bone. The cartilaginous cap is the site of growth, which normally diminishes after skeletal maturity. Whilst solitary osteochondroma (exostosis) is normally encountered within the first four decades [3], the hereditary and autosomal form predominantly occurs at a younger age and may present with limb shortening and deformity. Conventional radiology (using anatomical location, transitional zone and mineralisation of matrix) is used to diagnose chondroid tumours[4]. When there is no mineralisation of the cortex, diagnosis becomes more difficult and Computer Tomography (CT) or Magnetic Resonance Imaging (MRI) may be used. MRI provides excellent demonstration of arterial and venous compromise [5]. The most common characteristics include: endosteal scalloping, thick periosteal reaction and cortical hook. Only symptoms caused by the tumour warrant surgical removal and can provide excellent results [6].
    Giant cell tumour of bone Twenty per cent of all benign bone tumours are giant cell tumours (GCT), and mostly appear between the ages of 20 and 40 [7,8]. The location of GCTs can vary – most occur in the long bones, predominantly in the area of the knee (50–65%). Histologically, GCTs consist of giant cells with osteoclast like function surrounded by spindle-like stromal cells and other monocytic cells [7,9]. GCTs are usually benign (80%). However, recurrence after excision may occur in 20–50%, with 10% becoming malignant on recurrence [10]. GCTs appear on plain radiographs with the appearance of a lytic cystic lesion, with well defined, non-sclerotic margins [7,10]. These are usually located in the epiphysis of bones, with eccentric growth patterns. Other common features include cortical thinning, expansile remodelling of the bone, and prominent trabeculation [9]. In aggressive tumours radiographs may demonstrate cortical thinning, cortical bone destruction, and a wide zone of transition [9]. Pathologic fracture is a feature in between 11% and 37% of patients. [9,11] Although GCTs are usually diagnosed on the basis of radiographic evidence, a number of additional imaging tools may help to confirm the diagnosis. In 57% of cases ‘donut sign’ is present on bone scintigraphy, a result of increased peripheral uptake of radionuclide [12]. The use of CT imaging is helpful in examining the extent of the tumour margins. CT is superior to radiographic imaging in the recognition of certain features of GCTs, including cortical alterations and periosteal reactions [9]. MR imaging is the most accurate tool for demonstrating GCTs margins [9,13]. However, it is less effective than CT imaging at demonstrating changes in the cortex of the bone [13]. Functional imaging tools such fluoro-2-deoxy-d-glucose positron emission tomography have been identified as a potentially useful tool in identifying malignancy in musculoskeletal tumours [14]. There has been less research into the usage of PET in identifying benign bone tumours [15]. There is some evidence demonstrating that in PET giant cell tumours and other tumours containing giant cells display high FDG uptake [15–17]. It has been suggested that FDG PET may therefore be useful in the imaging of giant cell tumours after recurrence, where normal anatomy may be distorted [18].