Osteoma

Tumor biology and incidence

Benign, hamartomatous process
Slow-growing lesions of compact bone almost exclusively found in the craniofacial bones, projecting into the oral cavity and sinuses
Observed in 3% of patients requiring sinus radographs
Primary extracranial osteomas extremely rare; referred to as "parosteal osteomas"
Osteoma with cutaneous cysts, fibromatoses, and colonic polyps known as Gardner's Syndrome

Age

Most commonly diagnosed in the fifth decade; age range 16-74 years

Gender

M:F = 1:3

Presentation

Slowly enlarging, hard mass

Associated syndrome

Gardner's Syndrome

Physical findings

Palpable mass
Lesions in the head may cause:
- Facial asymmetry
- Difficulty breathing
- Eye problems
- Headache

Plain films

Site

Usually grows on the bone surface, but intramedullary cases have been described
Outer table of calvarium
Frontal and ethmoid sinuses
Occasionally long and short tubular bones

Size

Variable
Extracranial lesions are typically larger than cranial lesions; usually 1-4 cm

AP (left) and lateral tibia. Smoothly contoured, radiodense lesions attached to the cortical surface. Density is uniform and similar to that of cortical bone.

Tumor effect on bone

Focal, dense, homogenous bone
Well circumscribed geographic borders

Bone response to tumor

None

Matrix

Sclerotic matrix

Cortex

Smooth or lobulated surfaces
Surfaces merge with underlying cortical bone

Soft tissue mass

None

CT scan

Axial CT of the tibia

Coronal CT of the tibia

MRI

Axial T1 MRI of the tibia

Coronal T1 and T2 MRI of the tibia

PET CT

Differential diagnosis

Parosteal osteosarcoma
Osteochondroma
Reactive periosteal proliferations
- Fracture callus
- Periostitis ossificans
Sclerotic metastasis

Pathology

Gross: Heavily ossified tissue
Microscopic: Thickened sclerotic lamellar bone with minimal fibroblastic stroma
Etiology unknown
Theories:
- Non-aggressive osteoblastoma
- Hamartoma of periosteum
- Terminal ossified phase of fibrous dysplasia

Diagnosis and treatment

Excise if symptomatic, or for diagnosis if the lesion is large
Complete removal confers a cure

References