Topics

Topic

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Frontal bone

The frontal bone forms the anterior part of the skull, contributing to the forehead, roof of the orbits, and anterior cranial fossa. It consists of a squamous part forming the forehead and an orbital part forming the upper walls of the orbits. Inferiorly, it houses the frontal sinuses, which vary greatly in size among individuals.

The bone articulates with the parietal, nasal, maxillary, zygomatic, ethmoid, and sphenoid bones and plays a major structural and protective role. Its internal surface supports the frontal lobes of the brain, while its external surface contributes to facial contour. It is composed of an outer and inner table of compact bone separated by cancellous diploë, containing marrow and venous channels.

Synonyms

  • Os frontale

  • Forehead bone

  • Frontal region of calvarium

Location and Structure

  • Squamous part: Vertical portion forming the forehead.

  • Orbital part: Horizontal plates forming the orbital roofs.

  • Nasal part: Contributes to the root of the nose and articulates with nasal bones.

  • Frontal sinuses: Air-filled cavities within the frontal bone, lined by mucosa and connected to the nasal cavity.

  • Bone layers:

    • Outer table: thick compact bone

    • Diploë: cancellous bone with marrow

    • Inner table: thin compact bone adjoining dura

Relations

  • Superiorly: Parietal bones via coronal suture

  • Inferiorly: Orbits, ethmoid bone, and nasal bones

  • Posteriorly: Anterior cranial fossa and frontal lobes of the brain

  • Laterally: Zygomatic bones and sphenoid greater wings

  • Internally: Frontal lobes, meninges, anterior falx cerebri

Attachments

  • Dural attachment: Along internal surface, especially near midline and orbital plates

  • Muscular attachments:

    • Temporalis fascia (lateral aspects)

    • Occipitofrontalis (frontal belly attaches to skin overlying bone via galea aponeurotica)

Function

  • Protects frontal lobes of the brain

  • Forms structural support for orbit and forehead

  • Houses frontal sinuses facilitating resonance and reducing bone weight

  • Provides attachment surfaces for facial and scalp soft tissue

  • Contributes to upper facial contour and cranial vault stability

Clinical Significance (DESCRIPTIVE ONLY — NO PATHOLOGY APPEARANCE INCLUDED)

  • Important anatomical landmark in craniofacial imaging

  • Frequently assessed in trauma, sinus evaluation, and surgical planning

  • Frontal sinuses are highly variable and influence surgical approaches

MRI Appearance

T1-weighted images:

  • Outer and inner cortical tables: Very low signal (black)

  • Diploë: Bright signal due to fatty marrow content

  • Frontal sinus air: Very low signal (black)

  • Orbital roofs: Thin low-signal cortical lines

T2-weighted images:

  • Cortex: Low signal

  • Diploë: Intermediate-to-bright signal, less intense than on T1

  • Frontal sinus air: Low signal

  • Bone–soft tissue boundaries: Well defined, particularly at orbital roofs and anterior cranial fossa floor

STIR:

  • Cortex: Low signal

  • Diploë: Intermediate-to-dark signal (fat suppressed)

  • Frontal sinus: Black (air signal)

  • Enhances visibility of marrow-containing diploic space compared with surrounding cortical tables

T1 Fat-Saturated Post-Contrast:

  • Bone cortex: Non-enhancing, remains dark

  • Diploë marrow: Mild uniform enhancement

  • Frontal sinus walls: Thin non-enhancing lines

  • Adjacent dura: May show normal thin linear enhancement at skull base interfaces

CT Appearance

Non-Contrast CT:

  • Outer and inner tables: High-attenuation dense bone

  • Diploë: Lower attenuation cancellous bone with trabecular pattern

  • Frontal sinus: Air-filled cavity of very low attenuation

  • Orbital roof: Thin, well-defined high-density bone plate

  • Anterior cranial fossa floor: Smooth and sharply marginated

MRI images

Frontal bone axial mri image-img-00000-00000

CT image

Frontal bone axial ct image

CT VRT 3D image

Frontal bone 3d

X ray image

X ray Frontal bone anatomy image -img-00000-00000