Differentials
Ewing's sarcoma
SIGNS / SYMPTOMS
Same age range and predilection for males.
Type II symptoms (e.g., fever, night sweats) are usually seen.
INVESTIGATIONS
Conventional radiographs show a metaphyseal or diaphyseal tumour with a predominantly lytic appearance. No bone matrix is radiographically identified.
MRI shows a large soft tissue mass.
Biopsy shows a small blue cell tumour with no osteoid production and represents the confirmatory test.
Cytogenetic and/or molecular studies show the typical translocations/molecular aberrations of Ewing sarcoma family of tumours and help rule out small cell osteosarcoma (a rare sub-type of osteosarcoma with very little osteoid production).
Chondrosarcoma
SIGNS / SYMPTOMS
Most common in patients between 50 and 60 years of age.
The tumour has a predilection for the pelvic bones and a slower growth rate.
The main symptom is severe pain that is not relieved by rest and is worse at night.
INVESTIGATIONS
Conventional radiographs show a lytic lesion centred in the long bone metaphysis, with a permeative growth pattern scalloping the cortex and showing intra-tumoural calcifications, with a flocculent or ring-shaped appearance. The cortex is usually thickened with a slightly expanded and fusiform appearance, mainly due to the slow permeative growth of the tumour (chronic periosteal reaction). Scalloping of the inner cortex is a radiographic sign worrisome for malignancy.
Biopsy is the confirmatory test.
Malignant fibrous histiocytoma
SIGNS / SYMPTOMS
Most common in older patients.
Frequently presents with pathological fracture.
INVESTIGATIONS
Conventional radiographs show purely osteolytic tumour with minimal periosteal reaction.
Biopsy shows a typical spindle cell pleomorphic sarcoma with storiform architecture.
Giant cell tumour of bone
SIGNS / SYMPTOMS
Most common in skeletally mature women.
Usually presents with bone pain and sometimes pathological fractures.
INVESTIGATIONS
Conventional radiographs show tumour with an osteolytic appearance located in the epiphysis of long bones, with the distal femur and proximal tibia being the most commonly affected. Although benign, the tumour is locally aggressive. This translates radiographically into the absence of an osteosclerotic rim at its periphery as well as the presence of a soft tissue mass. No bone/osteoid formation is identified.
Biopsy shows typical appearance of evenly distributed giant cells in a mononuclear stroma. The nuclei of the giant cells resemble the nuclei of the mononuclear stromal cells.
Metastases from other malignancies
SIGNS / SYMPTOMS
Generally occur in older age group than osteosarcoma.
Usual history of a primary malignancy known to metastasise to bone, such as breast, lung, thyroid, kidney, and prostate.
INVESTIGATIONS
Conventional radiographs and radionuclide scans usually show osteolytic lesions (rarely osteoblastic) involving multiple bones.
CT imaging may reveal other organs affected by metastatic disease.
Biopsy usually confirms the diagnosis.
Lymphoma
SIGNS / SYMPTOMS
More common in older men.
Rare as a primary bone neoplasm. Type II general symptoms (e.g., fever, night sweats) and weight loss are common.
INVESTIGATIONS
Conventional radiographs may be normal (tumour cells tend to grow between patient's bony trabeculae with little bone destruction). There may be multiple or single bone involvement.
MRI shows focal change in the marrow signal.
Bone marrow biopsy is usually the confirmatory test.
Flow cytometric studies should be considered in patients suspected of having lymphoma.
Osteomyelitis
SIGNS / SYMPTOMS
Primary (haematogenous) osteomyelitis is associated with fever, local swelling, and fistula formation.
A history of recent trauma with open fracture is significant for secondary osteomyelitis.
INVESTIGATIONS
C-reactive protein and erythrocyte sedimentation rate are markedly elevated.
Biopsy shows necrotic bone, fibrotic marrow, and chronic inflammation with or without an acute inflammatory component.
Reactive bone is usually produced as part of an associated periosteal reaction.
Langerhans' cell histiocytosis
SIGNS / SYMPTOMS
Tends to have wide age distribution. However, 60% of cases arise in patients younger than 10 years of age.
Localised and systemic forms of the disease exist. Has a predilection for the bones of the skull, especially the calvarium, but any other bone can be involved.
Local pain and swelling are common.
INVESTIGATIONS
Erythrocyte sedimentation rate elevated.
Radiographically there are multiple lytic lesions with significant periosteal reaction.
Biopsy shows a proliferation of neoplastic Langerhans' cells in an inflammatory background.
Osteoblastoma
SIGNS / SYMPTOMS
Benign osteoid-producing tumour with roughly same age and sex distribution as osteosarcoma.
Pain of long duration is the most common presenting symptom.
For lesions located in the spine, scoliosis and neurological symptoms may occur.
INVESTIGATIONS
Conventional radiography reveals a radiolucent lesion in a long bone metaphysis or posterior arch of a vertebra, with a central area of radiodensity secondary to osteoid and bone production. No soft tissue mass is associated with the bone lesion.
Biopsy shows osteoid and woven bone rimmed by osteoblasts in a fibrovascular stroma.
Aneurysmal bone cyst
SIGNS / SYMPTOMS
Same age range and location as osteosarcoma.
Presents with pain and occasional pathological fracture. Secondary aneurysmal bone cysts can be seen in older patients, superimposed on other primary neoplasms.
INVESTIGATIONS
Conventional radiographs show radiolucent expansile bone lesion.
MRI shows fluid levels on T2-weighted images.
Biopsy can differentiate from telangiectatic osteosarcoma, which displays obvious histological features of malignancy (marked cellular pleomorphism, high and abnormal mitotic activity).
Fibrous dysplasia
SIGNS / SYMPTOMS
The presentation of polyostotic fibrous dysplasia commonly includes bone deformity and pathological fracture.
Wide age range at presentation and no male/female preference.
INVESTIGATIONS
Conventional radiographs show ground glass appearance with no associated soft tissue mass. There are generally no aggressive radiographical features. Pathological fracture may be seen.
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