Osteomas are benign bone tumors that most commonly occur in the head. When occurring in the medullary cavity osteomas are called bone islands 5.
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Terminology
Osteoma is the preferred terminology with ivory exostosis, parosteal osteoma, and maxillary/mandibular torus not recommended per the WHO classification of soft tissue and bone tumors (5th edition) 5.
Epidemiology
Osteomas are common with an equal male/female distribution 5.
Diagnosis
Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5th edition) 5:
essential: bone tumor with compatible imaging; tumor arises on the bone source or within the medullary cavity; composed of lamellar/cortical-type bone
Clinical presentation
These lesions are benign, slow growing, and usually asymptomatic. They may be incidentally identified as a mass in the skull or jaw, or as the underlying cause of sinusitis or paranasal sinus mucocele 5.
Pathology
Osteomas are benign osteogenic tumors composed of lamellar/cortical-type bone. The etiology is unknown 5.
Location
Osteomas most commonly occur in bones formed in membrane, almost exclusively occurring in the head 5, with the most common locations including:
Macroscopic appearance
These are well-cirumscribed tumors broadly attached to the bone surface 5.
Microscopic appearance
Two histological subtypes are recognized: compact and spongious. In cancellous bone, the bone marrow is filled with a well-vascularized and moderately cellular and fibrous stroma with inconspicuous osteoblasts and osteocytes and absent inflammatory infiltrate 5.
Associations
when multiple, Gardner syndrome should be considered 5
Radiographic features
Plain radiograph / CT
Osteomas appearing ivory-like as round, very radiodense lesions, similar to the normal cortex 5. Mature osteomas may demonstrate central marrow ref.
MRI
T1: low signal
T2: low signal 5
Nuclear medicine
Mild uptake may be seen on bone scintigraphy 5.
Treatment and prognosis
Osteomas are benign and only require excision if they cause adjacent complications (e.g. mucocele formation) or mass-effect (functional or cosmetic impairment). They can slowly grow 5.
History and etymology
Osteomas have been documented as far back as 664-332 BCE in ancient Egypt 5.
Differential diagnosis
Considerations include many cranial and facial bone lesions 6:
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