67. Benign and malignant bone tumours

Introduction

Primary bone tumors are considerably less common than bone metastases. We’ll discuss the primary bone tumors first.

The primary bone tumors range from benign to very malignant. They are divided into five subgroups:

• Bone-forming tumors
  • Osteoma
  • Osteoid osteoma
  • Osteoblastoma
  • Osteosarcoma
• Cartilage-forming tumors
  • Osteochondroma
  • Chondroma
  • Chondrosarcoma
• Fibrous and fibroosseous tumors
  • Fibrous cortical defect/nonossifying fibroma
  • Fibrous dysplasia
• Tumor-like lesions
  • Aneurysmal bone cyst
• Others
  • Giant cell tumor
  • Ewing sarcoma

Bone-forming tumours

These tumors are so named because they form osteoid, the unmineralized portion of bone. The osteoid may be mineralized to variable extent.

Osteoma:

• Benign tumor
• Exophytic masses of bones
• Most commonly occurs on the surface of facial bones, paranasal sinuses or the skull
• Associated with Gardner syndrome

Osteoid osteoma is a benign tumor of osteoblasts which affects young adults (10 – 30). It characteristically forms a nidus of osteoid which is surrounded by dense bone. The osteoid itself can be calcified to some extent. The tumor itself is usually around 1 cm in size, rarely larger than 1.5 cm. This tumor often occurs in the metaphysis of long bones, especially the femur.

The pain caused by osteoid osteoma is characteristic for the tumor. It causes intensive pain which is precise and not diffuse. The pain very typically becomes stronger during the night, and the pain can be effectively treated with NSAIDs. This is because the pain comes from prostaglandins produced by the tumor.

On x-ray there is a radiolucent central nidus which is rarely larger than 1.5 cm. The radiolucent nidus may be surrounded by a radiopaque ring.

Osteoblastoma is a benign tumor of osteoblasts which is very similar to osteoid osteoma in many ways. It’s similar as osteoid osteoma in that they both affect young adults and produce a radiolucent nidus. They’re different in these ways:

• Osteoblastomas are larger (> 2 cm)
• Often occur in parts of the vertebrae other than the vertebral bodies (the posterior column)
• The pain does not respond to NSAIDs and is not worse at night
• On the x-ray the radiolucent nidus is not surrounded by radiopaque bone

Osteosarcoma is a highly malignant tumor of osteoblasts. It’s most frequent in teenagers and elderly (50s). It has several risk factors:

• Paget disease of bone
• Hereditary retinoblastoma
• Irradiation
• Benign bone processes
  • Osteochondromatosis
  • Chondromatosis

It arises in the metaphysis of long bones, often in the distal femur or proximal tibia, meaning that it often occurs around the knee joint. It may manifest as a pathological fracture.

Osteosarcomas originate from the medulla of the bone, from which they frequently break through the cortex of the bone and “lift” the periosteum. This forms a characteristic picture on x-rays called the Codman triangle. A biopsy should always be performed to confirm the diagnosis.

These tumors frequently invade the surrounding soft tissue. They also metastasize to the lung in almost 100% of cases.

Treatment involves surgical removal and aggressive chemotherapy.

Cartilage-forming tumours

As these tumors form cartilage and not bone they’re often visible on x-ray as radiolucency inside the bones.

Osteochondroma is the most common benign tumor of bone. It produces a growth that grows laterally out of the epiphyseal growth plate. This growth has a cartilage cap on it.

Chondroma is a benign tumor of hyalin cartilage that occurs in bones of endochondral origin. It usually arises in the medulla of small bones of the hands and feet, especially in the proximal phalanges.

Chondroblastoma is a very rare benign tumor of cartilage.

Chondrosarcoma is a malignant tumor of cartilage. It affects adults in the 30 – 60 year range. It usually arises in the medulla of pelvic bones and the ribs. On x-ray osteolytic lesions with calcifications are typical.

These tumors vary from well differentiation to poorly differentiated. The well differentiated ones can be hard to distinguish from chondroma. The treatment of choice is surgical removal. This can be difficult due to the bones that are commonly involved. Its much more rare than its osteosarcoma counterpart.

Fibrous and fibroosseous tumours

Fibrous cortical defects are not true neoplasms but rather developmental malformations of the bone. They form sharply demarcated radiolucencies in bones, often close to the epiphysis of long bones. They are small lesions, often smaller than 0.5 cm in diameter. Larger lesions (5 to 6 cm) are called nonossifying fibromas. These conditions are often incidental findings and asymptomatic. They rarely require treatment.

Fibrous dysplasia is a benign tumor comprised of immature bone structures. They can manifest in three different ways:

• Monostotic – affecting only a single bone – 70% of cases
• Polyostotic – affecting multiple bones – 27% of cases
• As part of McCune-Albright syndrome – 3% of cases

McCune-Albright syndrome is a condition characterised by café au lait skin pigmentations, endocrine abnormalities and multiple fibrous dysplasias.

Other bone tumours

Giant cell tumor (osteoclastoma) arises in the epiphysis of the long bones, often in the distal femur or proximal tibia. It’s locally infiltrative, but almost never metastasizes. The tumor is comprised of two cell types: the neoplastic “stromal cells” and the reactive osteoclast-type giant cells. Looks like soap bubbles on X-ray,  should be easy to remember in this Corona time. Giant cell tumor are usually treated by curettage, but around 40-60% recur locally.

Ewing sarcoma is an aggressive malignant proliferation of poorly-differentiated cells from the neuroectoderm. It’s a type of primitive neuroectodermal tumor (PNET). It arises from the diaphysis of long bones, usually in male children.

A characteristic onion-skin pattern is visible on x-ray. t(11;22) translocation is common, which can be important during diagnosis. The tumor cells are PAS positive as they contain glycogen.

Metastases to the lung or other bones are frequent. Treatment involves high-dose irradiation, chemotherapy and surgical removal.

Tumour-like lesions

Aneurysmal bone cysts are blood-filled cysts with septa that form osteolytic lesions. They often occur in the spine and flat bones. The cysts are lined by fibroblasts and myofibroblasts, and the septa are comprised of osteoid and bone.

Metastatic tumours of the bone

Metastatic tumors of the bone are far more frequent than primary bone tumors. Bones are the third most common site of metastasis, after the lung and liver. They are often multiple rather than solitary. These metastases often originate from:

• Breast
• Lung
• Prostate
• Thyroid
• Kidney

Breast, lung and prostate account for 80% of cases.

Metastases most frequently form osteolytic lesions (decreased bone density) of the bone. A notable exception is metastases from the prostate, which form osteoblastic lesions (increased bone density). The most frequent symptom of bone metastasis is strong bone pain and pathological fractures.