Topics

Topic

design image
Frontal sinus

The frontal sinus is a paired, air-filled cavity located within the frontal bone, superior to the orbits and deep to the forehead. It is part of the paranasal sinus system and varies widely in size, shape, and degree of pneumatization among individuals. The two frontal sinuses are separated by an intersinus septum that is often asymmetric.

Each sinus drains into the middle meatus of the nasal cavity via the frontonasal duct and frontal recess, forming an essential component of the mucociliary drainage pathway. The sinus contributes to lightening the skull, humidifying inspired air, and providing resonance to the voice.

Synonyms

  • Sinus frontalis

  • Frontal paranasal sinus

Location and Structure

  • Position: Within the frontal bone, above the orbits and below the anterior cranial fossa.

  • Shape: Highly variable; may be asymmetrical, multiloculated, or hypoplastic.

  • Walls:

    • Anterior wall: Forehead surface of the frontal bone

    • Posterior wall: Forms part of the anterior cranial fossa

    • Inferior wall (floor): Forms part of the orbital roof

    • Medial wall: Inter-sinus septum

  • Drainage: Via frontonasal duct into the middle meatus through the frontal recess.

  • Lining: Respiratory mucosa (ciliated pseudostratified epithelium).

Relations

  • Superiorly: Anterior cranial fossa and frontal lobes

  • Inferiorly: Orbit and orbital roof

  • Medially: Contralateral frontal sinus (via septum)

  • Inferolaterally: Ethmoid labyrinth and frontal recess

  • Posteriorly: Dura mater of anterior cranial fossa

Function

  • Contributes to humidification and warming of inspired air

  • Lightens weight of the skull

  • Enhances resonance of voice

  • Provides a buffer against facial trauma

  • Participates in mucociliary clearance via frontonasal duct system

MRI Appearance

T1-weighted images:

  • Air-filled sinus: Very low signal (black)

  • Mucosal lining: Thin, low-signal layer along sinus walls

  • Bone cortex: Very low signal

  • Adjacent structures:

    • Orbital fat appears bright

    • Frontal lobe cortex shows intermediate signal

T2-weighted images:

  • Air within sinus: Very low signal (black)

  • Mucosa: Thin, intermediate-to-slightly bright linear signal

  • Bony boundaries: Low signal margins defining sinus shape

  • Surroundings: Ethmoid air cells appear with similar T2 low-signal air content

STIR:

  • Air cavity: Low signal (black)

  • Mucosal lining: Slightly brighter than on T1, but normally remains thin

  • Bone: Low signal

  • Soft tissues of forehead and orbit: Intermediate-to-bright depending on fat suppression

T1 Fat-Sat Post-Contrast:

  • Normal mucosal lining: Minimal or no noticeable enhancement

  • Sinus cavity: No enhancement (air)

  • Surrounding structures:

    • Nasal mucosa and turbinates enhance physiologically

    • Dura of anterior cranial fossa remains faintly enhancing

CT Appearance

Non-Contrast CT:

  • Sinus cavity: Appears as a well-defined air-filled space (very low attenuation, near –1000 HU)

  • Walls:

    • Anterior and posterior tables clearly visualized as dense cortical bone

    • Orbital roof forming sinus floor visualized with sharp bony margins

  • Inter-sinus septum: Well defined; may be midline or deviated

  • Drainage pathway: Frontal recess and frontonasal duct visible in relation to ethmoid air cells

Post-Contrast CT (standard):

  • Bone: No enhancement

  • Mucosa: Mild uniform enhancement if visible

  • Adjacent tissues: Enhancing nasal mucosa and ethmoidal structures help define sinus boundaries

  • Utility: Helps delineate sinus walls, frontonasal duct anatomy, and relationships with anterior cranial fossa

MRI image

Frontal sinus axial mri image-img-00000-00000

CT image

Frontal sinus ct sagittal image

X Ray image

Frontal sinus