Topics

Topic

design image
Ethmoid sinus

The ethmoid sinus consists of multiple thin-walled, air-filled cavities known as ethmoidal air cells, forming the ethmoid labyrinth. Located between the nasal cavity and the orbit, the ethmoid sinus lies within the ethmoid bone and is divided into anterior, middle, and posterior groups based on their drainage pathways.

These air cells contribute to humidification, mucus drainage, air filtration, and reduction of skull weight, while the complex bony partitions form critical boundaries with the orbit, skull base, and adjacent paranasal sinuses.

Synonyms

  • Ethmoidal air cells

  • Ethmoid labyrinth

  • Sinus ethmoidalis

Location and Structure

  • Situated between the nasal cavity and medial orbital wall, forming a honeycomb-like cluster of air cavities.

  • Comprised of 3–18 air cells, often categorized as anterior, middle, and posterior ethmoid cells.

  • Anterior ethmoid cells drain into the middle meatus via the ethmoidal infundibulum.

  • Posterior ethmoid cells drain into the superior meatus.

  • Boundaries include the lamina papyracea, cribriform plate, fovea ethmoidalis, and middle turbinate.

Relations

  • Laterally: Orbit and lamina papyracea

  • Medially: Middle nasal meatus, middle turbinate, and superior turbinate

  • Superiorly: Anterior cranial fossa, cribriform plate, and olfactory mucosa

  • Inferiorly: Ethmoidal bulla and nasal cavity

  • Posteriorly: Sphenoid sinus

  • Anteriorly: Frontal recess and frontal sinus drainage pathway

Attachments / Structural Connections

  • Middle turbinate: Attached to the ethmoid bone and forms medial wall of ethmoid labyrinth

  • Uncinate process: Forms part of lateral nasal wall and influences drainage

  • Ethmoid bulla: Largest anterior ethmoid air cell contributing to middle meatus structure

Function

  • Humidifies and warms inhaled air

  • Reduces weight of the skull

  • Provides structural support to the nasal cavity and medial orbital wall

  • Participates in mucociliary clearance through mucosal lining

  • Contributes to resonance of voice

Clinical Significance

(Only general significance without pathology description)

  • Important region in image-guided sinus surgery and skull base approaches

  • Landmark for orbital and anterior cranial fossa boundaries

  • Critical site for identifying variations such as Haller, Onodi, or agger nasi cells

MRI Appearance

T1-weighted images:

  • Aerated ethmoid cells: Low signal intensity (dark)

  • Mucosal lining: Thin intermediate signal

  • Bony septations: Very low signal (black)

  • Adjacent orbital fat: Bright, providing contrast with ethmoid walls

T2-weighted images:

  • Air-filled ethmoid cells: Very low signal

  • Mucosal lining: Intermediate-to-high signal depending on thickness

  • Bone: Low signal

  • Clear delineation of orbital boundaries and ethmoidal roof

STIR:

  • Air spaces: Dark signal

  • Mucosal lining: Intermediate signal

  • Adjacent fat is suppressed, enhancing contrast between sinus mucosa and surrounding structures

T1 Fat-Sat Post-Contrast:

  • Normal mucosal lining: Thin, mild, uniform enhancement

  • Bone: Non-enhancing

  • Enhancing periosteum and mucosal interfaces help define sinonasal anatomy

CT Appearance

Non-Contrast CT:

  • Air-filled ethmoid cells: Very low attenuation (dark)

  • Thin bony septa: High-attenuation linear structures

  • Lamina papyracea: Thin, well-defined bony medial orbital wall

  • Cribriform plate: Delicate bony roof of ethmoid labyrinth

  • Excellent visualization of complex cell anatomy and drainage pathways

Post-Contrast CT:

  • Used primarily to highlight adjacent soft tissues

  • Normal mucosa: Thin symmetric enhancement

  • Ethmoid roof and lamina papyracea remain non-enhancing bony structures

  • Provides improved soft-tissue contrast for evaluating nasal cavity and periosteal surfaces

MRI image

ethmoid sinus axial mri image-img-00000-00000

CT image

ethmoid sinus ct sag image

X Ray image

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