Last revised by Frank Gaillard on 27 Jan 2024

Osteomas are benign bone tumors that most commonly occur in the head. When occurring in the medullary cavity osteomas are called bone islands 5.

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.

Osteomas are common with an equal male/female distribution 5.

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

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.

Osteomas are benign osteogenic tumors composed of lamellar/cortical-type bone. The etiology is unknown 5.

Osteomas most commonly occur in bones formed in membrane, almost exclusively occurring in the head 5, with the most common locations including:

These are well-cirumscribed tumors broadly attached to the bone surface 5.

Osteoma are primarily comprised of mature lamellar bone and divided into two histological subtypes based on their architecture: compact and cancellous or spongious 9,10.

The compact osteoma is comprised almost exclusively of mature lamellar bone with minimal if any bone marrow spaces and occasional Haversion canals 9.

Cancellous or spongious oteomas contain the bone marrow is filled with a well-vascularized and moderately cellular and fibrous stroma with inconspicuous osteoblasts and osteocytes and absent inflammatory infiltrate 5,9.

When osteomas are multiple, Gardner syndrome should be considered 5,10. These are due to mutations in the APC gene 5,10.

In addition to cases occurring in the setting of Gardner syndrome, sporadic osteomas have also been shown to demonstrate frequent mutations in CTNNB1 gene (encoding β-catenin) 10.

Osteomas appearing ivory-like as round, very radiodense lesions, similar to the normal cortex 5. They usually arise on the skull outer surface (outer table) but can occur in the intramedullar or inner surface (inner table) of the skull 8. Some mature osteomas may demonstrate central marrow 8.

The MRI appearance will depend on the presence and quantity of bone marrow within the osteoma 5,7,8.

  • T1

    • usually low signal

  • T2

    • variable, depending on amounts of cortical and trabecular bone

  • T1 C+

    • no enhancement

Mild uptake may be seen on bone scintigraphy 5.

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.

Osteomas have been documented as far back as 664-332 BCE in ancient Egypt 5.

Considerations include many cranial and facial bone lesions 6:

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