Benign Bone Tumors

Overview

Osteoid osteomas and osteoblastomas are bone-forming lesions found in children; osteomas can also be seen in adults. Osteochondromas are cartilage-forming tumors. Giant-cell tumors are osteolytic. Fibromas and bone cysts are other benign bone lesions.

Characteristics of benign bone tumors

• Noncancerous, do not spread to other body parts
• May cause pain 
• Range from static lesions (remain essentially unchanged) to locally aggressive lesions (expand until treated, but are still benign)
• Characteristic radiographic features are seen on x-rays. 
• Often discovered incidentally
• Osteoid osteoma: 
  • Morphologically and genetically similar to osteoblastoma
  • May be 2 different presentations of the same genetic entity

Epidemiology

• Osteochondromas are the most common type of benign bone tumors: 30%–35%
• Giant-cell tumors: 20%
• Osteoblastomas: 14%
• Osteoid osteomas: 12%
• All others: less common

Staging and classification

• Staging:
  • Latent: asymptomatic; discovered incidentally
  • Active: mild symptoms; continued tumor growth
  • Aggressive: grow rapidly
• Classification:
  • Diaphyseal
  • Metaphyseal
  • Epiphyseal

Osteoid Osteoma (in Children)

Description

• Bone-forming hamartomatous lesion seen in young people
• Ovoid: nidus < 2 cm
• Predominantly located in the cortex of metaphysis and diaphysis (80%–90%) of long bones
• Locations:
  • Most common:
    • Proximal femur
  • Other locations:
    • Tibia
    • Spine
    • Other parts of the femur

Epidemiology

• Peak incidence: age 10–30 years (90% < age 25)
• Affects males 2–3 times more often than females

Clinical features

• Often asymptomatic and discovered incidentally
• When symptomatic, presents with:
  • Pain:
    • Constant, intense 
    • Worse at night
    • Manifests before the lesions are visible on x-ray
  • Swelling
  • Deformity
  • Pathologic fracture
• Spine lesions may present with:
  • Limping
  • Scoliosis
  • Localized tenderness
  • Restriction of motion
  • Paravertebral muscle spasm

Diagnosis

• X-ray or CT: 
  • Radiolucent core (nidus) surrounded by sclerosis
  • Cortical thickening 
  • Diffuse medullary sclerosis 
  • 25%–40% not seen on x-ray and need CT imaging for visualization
  • MRI not recommended: shows soft-tissue edema, which may obscure the nidus
• Scintigraphy: intense enhancement; accurate in localizing the nidus
• Histology: almost identical to osteoblastoma, osteosarcoma, and enostosis

Management

• NSAIDs: effective because the nidus produces high levels of prostaglandins
• Surgical removal: if pain is unresponsive to medical treatment

Osteoma (in Adults)

Description

• Differ from osteoid osteomas in that osteomas are solid, bony growths (as opposed to a radiolucent nidus surrounded by sclerosis).
• Benign, round, bone-forming tumors on the cortical surface of a bone
• Well-defined and solitary
• Diameter usually < 1 cm
• Arises from osteoblasts:
  • Compact osteomas: composed of mature lamellar bone
  • Spongy osteomas: composed of trabecular bone with marrow

Epidemiology

• May develop at any age, but most common in middle-aged individuals
• Occur in men slightly more often than in women 
• Associated with Gardner syndrome as an extracolonic manifestation of familial adenomatous polyposis

Clinical presentation

• Usually discovered incidentally; often asymptomatic
• May be symptomatic, causing serious “mass effect” symptoms (even though they are considered benign)
• Location: may cause the following symptoms:
  • In facial bones, may cause:
    • Disturbances in vision and hearing
    • Cranial-nerve palsies/proptosis
    • Facial asymmetry
  • In cranial bones (especially paranasal sinuses), may cause:
    • Secondary sinus obstruction/congestion
    • Headaches
  • Vertebral column: may cause spinal cord compression
• Radiologic findings on x-ray or CT:
  • Radiodense, well-circumscribed, round to ovoid lesions 
  • Do not penetrate the surrounding soft tissues

Management

• Asymptomatic → no treatment
• Symptomatic tumor growth → surgery

Osteoblastoma

Description

• Bone-forming lesion
• Predominantly cortical tumor
• Larger than osteoid osteoma (> 2 cm)
• Predominance of metaphyseal over diaphyseal locations
• May be locally aggressive

Epidemiology

• Approximately 14% of benign bone tumors
• Peak incidence: age 10–30 years
• Male-to-female predominance: 2.5 to 1

Clinical features

• Location: 
  • Involve the axial skeleton
  • Vertebral lesions often involve the posterior elements (vertebral arch).
• Presentation:
  • Insidious, dull pain; worse at night 
  • Painful scoliosis if vertebral lesion present
  • Neurologic symptoms if spinal cord compression present

Diagnosis

• X-ray: 
  • Predominantly lytic lesions with a rim or perifocal sclerosis
  • May have internal calcification or “bubbly” appearance
  • Majority of individuals will have rapid cortical expansion:
    • Sometimes cortical destruction
    • Approximately 50% have surrounding sclerosis or periostitis.
• CT:
  • Lesions demonstrated as lytic, similar to x-ray
  • Internal matrix mineralization is better seen on CT.
• MRI:
  • Features may overestimate the lesion.
  • Decreased areas of intensity correspond to foci of calcification.
  • Usually highly vascular and enhance significantly with gadolinium

Management

• Asymptomatic → no treatment
• Majority not responsive to NSAIDs
• Surgery:
  • Resection of the nidus for refractory symptoms
  • Curettage and bone grafting preferred
• Follow-up x-rays every 4–5 months

Osteochondroma

Description

• Appearance: bony exostosis (spur) with a cartilage cap
  • Cartilage cap is thick in children (> 2 cm).
  • Thinner in adults (< 1 cm)
• Location: 
  • Metaphysis of long bones adjacent to growth plates 
  • Approximately 50% occur around the knee–distal femur or proximal tibia.
  • Also seen in the proximal humerus

Epidemiology

• Most common primary benign bone tumor:
  • 30% of all benign bone tumors 
  • 9% of all bone tumors
• Peak incidence: age 10–30 years
• Sex: male > female
• Hereditary multiple osteochondromas: autosomal dominant disease characterized by several bone lesions

Clinical presentation

• Usually asymptomatic
• Can be palpable near the ends of long bones
• If symptomatic with pain, the pain is due to the direct mass effect on surrounding soft tissue.

Diagnosis

• X-ray: 
  • Osseous spur that arises from the surface of the cortex.
  • May be sessile (base > cap) or pedunculated (cap > base)
  • Usually involves the metaphysis
• MRI:
  • Warranted if concern for adjacent tissue impingement
  • Indicated if potential for surgical resection

Management

• Most cases do not need treatment.
• Symptomatic cases → excision
• Approximately 1% transform into a chondrosarcoma.

Giant-Cell Tumor

Description

• Also known as “osteoclastoma”
• Benign but locally aggressive tumor
• Composed of giant cells that arise from the bone marrow.
• Affects the epiphysis of long bones (usually near the knee)

Epidemiology

• Peak incidence: age 20–40 years
• Rate overall: 1.3 cases per million people per year
  • 15%–20% of all benign bone tumors
  • 3%–5% of all primary bone tumors

Clinical presentation

• Found in the epiphysis or metaphysis of long bones
• 50% around the knee
• Pathologic fractures
• Local pain and swelling
• Limited range of motion

Diagnosis

• X-ray: multicystic osteolytic lesions (“soap bubble” appearance) 
• Biopsy/histopathology:
  • Not completely understood to be neoplastic
  • Multinucleated giant cells are reactive and resemble osteoclasts.
  • Receptor activator of nuclear factor kappa-B ligand (RANKL)–expressing cells:
    • Also known as “osteoclast differentiation factor”
    • Highly expressed by the stromal cells within giant-cell tumors
    • RANKL expression by the stromal cells → recruitment of osteoclastic cells 

Management

• Comprehensive histologic sampling is needed to ensure diagnosis.
• Surgery: 
  • Curettage and bone grafting
  • En bloc resection to minimize recurrence rate
• Watchful follow-up for recurrence

Prognosis

• Typically benign; rare risk of malignant degeneration ↑ with age (approximately 4%)
• Tendency for significant bone destruction and local recurrence

Differential Diagnosis

• Osteosarcoma: primary malignant tumor of the bone characterized by the production of osteoid or immature bone by the tumor cells. Osteosarcoma is most common in children and young adults, and it presents with pain and swelling, sometimes with a palpable mass, or as a pathologic fracture. Diagnosis is established with imaging studies and biopsy. Management involves systemic chemotherapy and surgical resection. 
• Ewing sarcoma: primary bone malignancy derived from primitive round cells. Ewing sarcoma affects primarily children and teenagers and commonly presents with a painful mass, swelling, and pathologic bone fractures. Diagnosis is established with imaging and biopsy. Treatment involves systemic chemotherapy and local control of the tumor with surgical resection or radiation. With proper treatment, the overall 5-year survival is over 70%.
• Chondrosarcoma: malignant bone tumor characterized by the production of a cartilaginous matrix. Chondrosarcoma usually presents with a slowly increasing mass or swelling and dull, aching pain. Depending on the location, the condition may also be associated with symptoms of nerve compression. The diagnosis is established on the basis of characteristics found on imaging and tissue biopsy results. The mainstay of treatment is surgical excision.
• Multiple myeloma: malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Diagnosis is established by plasma electrophoresis and bone marrow biopsy. Some low-risk individuals may remain stable for years without treatment, while others may progress despite treatment. Chemotherapy is indicated for individuals who meet high-risk criteria.
• Craniopharyngiomas: rare squamous epithelial tumors with a solid and/or cystic structure that arise from the remnants of the Rathke pouch along the pituitary stalk in the suprasellar region. Symptoms of craniopharyngiomas include headaches, nausea, vomiting, visual disturbances, endocrine dysfunction, and behavioral issues. Diagnosis is made by imaging and biopsy. Management involves surgical excision and radiation therapy.