Paranasal Sinuses

• Frontal - pair
• Ethmoidal - pair
• Spenoidal
• Maxillary - pair

Frontal Sinus

• Lies between the outer and inner tables of the frontal bones. 
• It is variable in size. 
• It may be absent.
• It may extend up to the sphenoid.
• The fontal sinus empties into the middle meatus through the ethmoidal infundibulam or frontonasal duct.

Ethmoidal

• They lie between the orbit and the upper part of the nasal cavity.
• It connects the multiple thin walled cavities. 
• It has multiple communications with the nasal foscia. 
• The sinus is separated from the orbit by the thin orbital plate of ethmoid. 
• Infection may spread to the orbit from sinuses through this, causing orbital cellulitis.

Sphenoidal Sinuses

• Contained within the body of the sphenoid bone. 
• They may communicate. 
• One may be longer than the other.
• Relationship: Superiorly - Pituitary, optic chiasma

Maxillary Sinus

• Longest paranasal sinus.
• Occupy the maxillary bone.
• Pyramidal in shape.
• Roof formed by floor of orbit
• Floor formed by alveolar process (Roots of teeth may project into the sinus).
• Medially - Nasal Fossa.
• Laterally - Zygomatris process.
• Drains into the middle meatus.