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Sphenoid sinus

The sphenoid sinus is a paired, air-filled paranasal sinus located within the body of the sphenoid bone, positioned centrally in the skull base. It varies widely in size and degree of pneumatization, often extending into the clivus, greater wings, lesser wings, and pterygoid processes depending on anatomical variation.

The sphenoid sinus forms a critical anatomical boundary between the nasal cavity and numerous vital neurovascular structures, including the optic nerve, internal carotid artery, cavernous sinus, pituitary gland, and cranial base dura.

Synonyms

  • Sinus sphenoidalis

  • Sphenoidal sinus

Location and Structure

  • Situated in the center of the skull base within the body of the sphenoid bone

  • Typically divided by a midline septum that may attach asymmetrically to adjacent structures

  • Opens into the sphenoethmoidal recess in the superior nasal cavity

  • Pneumatization patterns include: conchal (minimal), presellar, sellar, and postsellar types

  • Air-filled cavity lined by respiratory mucosa

Relations

  • Superiorly: Sella turcica, pituitary gland, optic chiasm

  • Inferiorly: Nasopharynx and roof of posterior nasal cavity

  • Laterally: Cavernous sinus, internal carotid arteries

  • Posteriorly: Clivus and brainstem dura

  • Anteriorly: Sphenoethmoidal recess and posterior ethmoid air cells

Function

  • Lightens the skull while maintaining structural integrity

  • Contributes to humidification and warming of inhaled air

  • Acts as a resonance chamber for voice

  • Serves as a surgical corridor in transsphenoidal pituitary approaches

MRI Appearance

T1-weighted images:

  • Air within sphenoid sinus: very low signal (dark)

  • Mucosa lining the sinus: thin intermediate-to-low signal

  • Bony walls: uniformly low signal

  • Surrounding structures:

    • Pituitary and cavernous sinus: intermediate signal

    • Marrow of sphenoid bone (if present): bright fatty signal

T2-weighted images:

  • Air: dark signal

  • Mucosal lining: thin intermediate-to-slightly bright signal

  • Bony boundaries: low signal

  • Adjacent neurovascular structures clearly defined due to high soft-tissue contrast

STIR:

  • Air: dark signal

  • Mucosal lining: intermediate signal

  • Bony cortex: low signal

  • Fatty marrow of sphenoid body: suppressed to low signal

T1 Fat-Sat Post-Contrast:

  • Normal mucosal lining: thin uniform mild enhancement

  • Bony walls: non-enhancing, low signal

  • Adjacent dura and cavernous sinus structures: enhance normally

CT Appearance

Non-Contrast CT:

  • Air: very low density (black)

  • Bony walls: sharply defined high-attenuation structures

  • Septations: visible as thin bony partitions within cavity

  • Pneumatization of clivus or wings clearly depicted

  • Excellent delineation of optic canal, carotid canal, and skull base boundaries

Post-Contrast CT:

  • Air cavity: non-enhancing

  • Sinus mucosa: thin uniform enhancement

  • Walls and septa: unchanged dense bony attenuation

  • Adjacent structures such as cavernous sinus and nasal mucosa enhance appropriately

MRI image

sphenoid sinus cells axial mri image-img-00000-00000

CT image

sphenoid sinus CT sag image

CT image

Sphenoid sinus CT