Paranasal sinuses

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:

1. Frontal Sinuses
2. Ethmoidal Sinuses
3. Maxillary Sinuses
4. 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.