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.
