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Sphenoidal sinus

The sphenoidal sinus is a paired air-filled cavity located within the body of the sphenoid bone at the skull base. It is the most posterior of the paranasal sinuses and shows marked anatomical variability in size, shape, and pneumatization. Owing to its deep central location and close relationships with critical neurovascular structures, the sphenoidal sinus is of major importance in radiology, endoscopic sinus surgery, and skull base approaches.

Synonyms

  • Sphenoid sinus

  • Sphenoid air sinus

Location

  • Located within the body of the sphenoid bone

  • Posterior to the nasal cavity

  • Inferior to the sella turcica and pituitary gland

  • Anterior to the clivus and brainstem

  • Superior to the nasopharynx

  • Separated into right and left sinuses by an intersinus septum (often asymmetric)

Anatomical components

  • Right and left sphenoidal sinuses

  • Intersinus septum:

    • Often deviated from the midline

  • Ostium of sphenoidal sinus:

    • Opens into the sphenoethmoidal recess

  • Mucosal lining:

    • Respiratory epithelium

  • Bony walls:

    • Thin and closely related to adjacent structures

Relations

Superiorly:

  • Sella turcica and pituitary gland

  • Optic chiasm (variable proximity)

Inferiorly:

  • Nasopharynx

Anteriorly:

  • Posterior nasal cavity

  • Sphenoethmoidal recess

Posteriorly:

  • Clivus

  • Pons

Laterally:

  • Cavernous sinus

  • Internal carotid artery

  • Optic nerve (optic canal)

Developmental anatomy

  • Absent at birth

  • Begins pneumatization: Around 3–4 years of age

  • Continues to expand: Through childhood and adolescence

  • Adult configuration: Usually achieved by late teenage years

  • Variants:

    • Conchal, presellar, or sellar types based on pneumatization

X-ray appearance

Skull radiographs (lateral / occipitomental views):

  • Sphenoidal sinus: Radiolucent air-filled space posterior to nasal cavity

  • Margins: Thin bony outlines

  • Visualization: Limited due to overlap of skull base structures

  • Utility: Largely supplanted by CT

CT appearance

Non-contrast CT:

  • Gold standard for evaluation

  • Air-filled sinus: Hypodense cavity within sphenoid body

  • Bony walls: Thin, well-defined cortices

  • Intersinus septum: Often asymmetric

  • Relationships: Clearly demonstrates proximity to optic canal, carotid canal, and sellar floor

Post-contrast CT:

  • Sinus cavity: No enhancement

  • Mucosa (if visible): Thin non-enhancing lining

  • Vascular structures: Cavernous sinus and internal carotid artery enhance normally

3D CT VRT appearance

Volume-rendered technique (VRT):

  • Sphenoid body: Central skull base structure with variable sinus cavity contour

  • Pneumatization pattern: Clearly appreciated

  • Bony landmarks: Optic canal, carotid canal, and sellar floor well demonstrated

  • Surgical utility: Excellent for preoperative skull base planning

MRI appearance

T1-weighted images:

  • Normally aerated sinus: Signal void (very low signal)

  • Bony walls: Low signal

  • Adjacent pituitary gland: Intermediate signal

T2-weighted images:

  • Air-filled sinus: Signal void

  • Thin mucosa: Usually not conspicuous

  • CSF in adjacent cisterns: High signal

MRI images

MRI Sphenoidal sinus anatomy image -img-00000-00000

MRI images

MRI Sphenoidal sinus anatomy image -img-00000-00000_00001

X-Ray image

X ray Sphenoidal sinus anatomy image -img-00000-00000