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Paranasal sinuses
Air-filled spaces around the nasal cavity
RegionHead and Neck
SystemRespiratory System
Paranasal sinuses are air-filled cavities located within the bones of the skull and face, surrounding the nasal cavity. These sinuses are lined by a mucous membrane that is continuous with the nasal mucosa. They play essential roles in lightening the skull, humidifying and warming inhaled air, enhancing voice resonance, and providing a buffer against facial trauma.[7]
The paranasal sinuses are categorized into four paired groups based on their anatomical location:
- Frontal Sinuses
- Ethmoidal Sinuses
- Maxillary Sinuses
- Sphenoidal Sinuses
Anatomy and Location
1. Frontal Sinuses
- Location: Found in the frontal bone, above the eyebrows.[8]
- Size and Shape: Varies in size and can be asymmetrical; often divided by a septum.
- Drainage Pathway: Drains into the middle meatus of the nasal cavity through the frontonasal duct.
2. Ethmoidal Sinuses (Ethmoid Air Cells)
- Location: Positioned between the eyes within the ethmoid bone.
- Subdivisions:
- Anterior Cells: Drain into the middle meatus.[5]
- Posterior Cells: Drain into the superior meatus.
- Structure: Consist of multiple small air cells separated by thin bony walls.
3. Maxillary Sinuses
- Location: Situated within the maxilla, below the eyes and above the upper teeth.
- Size and Shape: Largest of all the sinuses; pyramidal in shape.[1]
- Drainage Pathway: Drains into the middle meatus through the semilunar hiatus.
- Special Note: Closely related to the roots of the upper molar teeth, making it prone to dental infections.
4. Sphenoidal Sinuses
- Location: Located within the body of the sphenoid bone, behind the eyes and below the brain.[3]
- Size and Shape: Varies in size and may be asymmetrical.[4]
- Drainage Pathway: Drains into the sphenoethmoidal recess above the superior concha.
- Special Note: Close to important structures like the optic nerve and pituitary gland.
Function
- Air Filtration and Humidification: The mucosal lining filters and humidifies the air before it reaches the lungs.
- Voice Resonance: The hollow spaces in the sinuses enhance vocal tone and resonance.
- Cranial Lightening: Reduces the overall weight of the skull, making it less dense and more balanced.[6]
- Protection: Acts as a cushion against facial trauma, absorbing impacts to protect delicate structures like the brain and eyes.
- Immune Defense: Produces mucus that traps and eliminates pathogens, supported by ciliary movement.
Clinical Significance
- Sinusitis:
- Inflammation or infection of the sinuses, leading to symptoms like nasal congestion, facial pain, headache, and nasal discharge.
- Classified into acute, subacute, and chronic sinusitis.
- Mucoceles:
- Mucus-filled cysts that form due to obstruction of sinus drainage.
- Commonly affect the frontal and ethmoidal sinuses.
- Nasal Polyps: Benign growths originating from the sinus mucosa, causing obstruction and difficulty breathing.
- Sinus Tumors: Rare but may present as squamous cell carcinoma, adenocarcinoma, or lymphoma.
- Dental Infections: Maxillary sinuses are prone to infections spread from the upper teeth, especially molars, due to their proximity.[2]
- Cerebrospinal Fluid (CSF) Leak: Trauma or surgery involving the sphenoid or ethmoid sinuses can lead to CSF leakage, posing a risk of meningitis.
- Orbital Complications: Infections in the ethmoidal sinuses can spread to the orbit, leading to conditions like orbital cellulitis and abscesses.
- Surgical Relevance: Procedures like functional endoscopic sinus surgery (FESS) are used to restore drainage pathways and treat chronic sinusitis.
Published on January 7, 2025
Last updated on April 24, 2025
Last updated on April 24, 2025