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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

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

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