Bone Tumours and Neuroblastoma in Children

Osteosarcoma

Osteogenic sarcoma (OS) is the most common primary malignant tumour of bone in children and accounts for 55% of all bone tumours seen in adolescence. The aetiology is unknown but there are recognised associations with previous retinoblastoma, previous treatment with an alkylating agent, previous radiotherapy as well as with some genetic syndromes, such as Rothmund–Thomson syndrome. Often patients have a history of trauma, which brings the problem to clinical attention.

Radiographically, OS is variable but most frequently appears as a destructive metaphyseal long bone lesion with poorly demarcated margins, osteoid production, aggressive periosteal reaction and a soft-tissue mass ( Fig. 75.1 ). The lesion may cross the growth plate. Locoregional staging is performed using MRI and pulmonary metastatic disease is assessed using CT. Distant bony metastases are usually assessed using scintigraphy but may also be assessed using whole-body MRI.

MRI staging should include wide field-of-view T ₁ weighted sequences to assess the entire bone involved and the contralateral side to look for skip and synchronous contralateral lesions.

Paediatric OS variants include telangiectatic OS, characterised by dilated blood-filled cavities; periosteal OS arising from the deep periosteal layer; and high-grade surface OS involving the bone surface.

Treatment with chemotherapy may lead to a decrease in tumour volume, haemorrhagic signal change and organisation of periosteal reaction. Diffusion-weighted imaging, dynamic MRI contrast imaging and positron-emission tomography (PET) are all said to assess tumour response and necrosis fraction, an important prognostic indicator, but these are currently research tools.

The Ewing Sarcoma Family of Tumours

The Ewing sarcoma family tumours are the second most common bone tumours in adolescents and children. The pathogenesis of ESFTs is unknown. They occur more commonly in adolescents but a peak of incidence in very young children is well recognised. Classically, flat bone involvement (such as ribs or iliac bone) is seen in ESFTs, but any bone may be involved, with 50% arising in the femur or pelvis.

The clinical presentation is non-specific: local pain, fever and swelling can mimic osteomyelitis or non-infectious osteitis/chronic relapsing multifocal osteomyelitis, delaying the diagnosis. Children with a chest wall tumour usually present with pain. The initial destructive rib lesion is often initially overlooked; by the time of diagnosis, a pleural effusion is usually present. Metastatic spread is haematogenous, and metastases occur to the lungs, bones and bone marrow. Lymph node, liver and skip metastases are rare. Radiographic features include a permeative appearance, with an ‘onion skin’ periosteal reaction. There is often a large associated soft-tissue mass ( Fig. 75.2 ), which in the case of pelvic origin tumours may not be clinically apparent and radiographically may be difficult to interpret, possibly delaying diagnosis. ESFT staging is as for OS; however, PET may have some advantages over scintigraphy in evaluating bone metastases in ESFTs.

Bone Metastases

Bone metastases are not as common in children as compared with adults. Metastases as the first manifestation of an occult primary tumour are unusual, as in children the primary tumour is usually evident initially. Metastatic bone disease in children is most frequently due to leukaemia and neuroblastoma, but lymphoma, ESFT, rhabdomyosarcoma and medulloblastoma may metastasise to bone ( Figs 75.3 and 75.4 ).

Lytic appearances and/or periosteal reactions are the most common radiographic characteristics in metastatic lesions, but sclerotic lesions are also reported, particularly in medulloblastoma and leukaemia. Metaphyseal radiolucent lines are typically described in leukaemia and, less commonly, neuroblastoma. Bone scintigraphy, MRI or metaiodobenzylguanidine (mIBG) studies may be utilised, depending on the clinical scenario.

Rare Malignant Bone Tumours in Children

• Chondrosarcoma

• Primary malignant lymphoma of bone

• Haemangiosarcoma of bone

  Summary Box: Malignant Bone Tumours

  • Osteosarcoma is the most common primary malignant bone tumour in paediatric practice. OS typically appears as a bone forming lesion affecting long bones.

  • Ewing Sarcoma is the second most common primary malignant bone tumour encountered. ES classically affects flat bones and is often associated with a large extra-osseous soft tissue mass.

  • Local staging is performed using MRI and pulmonary metastatic disease assessed using CT.

  • Metastatic bone lesions in children are most commonly seen with Neuroblastoma, leukaemia and lymphoma

Bone-Forming Tumours

• Enostosis (bone island)

• Osteoid osteoma

• Osteoblastoma

Osteoid Osteoma

This painful lesion composed of woven bone and osteoid occurs in children and adolescents, but more than 80% of cases occur in the second decade of life. The pain is typically worse at night and relieved by aspirin or other related non-steroidal anti-inflammatory agents. Classically, lesions occur in tubular bones, but they may also affect the vertebrae, presenting clinically with painful scoliosis, seen as a dense pedicle, or may be identified following positive scintigraphy. Osteoid osteoma may be polyostotic.

Plain radiographs, supplemented by CT with direct visualisation of a central nidus and surrounding a sclerotic reaction, provide the diagnosis ( Fig. 75.5 ). Sometimes the nidus may contain calcification. On MRI, cortical thickening returns a low signal on all sequences. The nidus has a variable appearance, depending on the site and relative amounts of osteoid and matrix. There may be prominent soft-tissue or bone marrow oedema, which may lead to diagnostic confusion ( Fig. 75.6 ).

A typical tumour pattern on three-phase skeletal scintigrams is described, characterised by focal hypervascularity and high uptake. A negative scintigram excludes the presence of osteoid osteoma. Scintigraphy can confirm recurrence or incomplete removal if pain persists following surgery. Historically, surgical treatment has been the mainstay; however, image-guided ablation therapy—for example, using radiofrequency or high-intensity focused ultrasound (HIFU)—is now possible.

Osteoblastoma

Osteoblastoma is rare and difficult to differentiate histologically from osteoid osteoma, although it is distinct radiographically, with a nidus measuring greater than 1.5 to 2 cm in diameter. The main sites are the posterior elements of the spine. Radiographically, osteoblastoma is expansile and may be either lucent or sclerotic, with a sclerotic rim ( Figs 75.7 and 75.8 ). The cortex may occasionally be broken. There is usually surrounding oedema ( Fig. 75.9 ).

Tumours of Fibrous Tissue Origin

• Non-ossifying fibroma (NOF)

• Metaphyseal fibrous cortical defects

• Fibrous bone dysplasia (FBD) (Jaffe–Lichtenstein)

• Osteofibrous bone dysplasia (OBD) (Campanacci)