Paranasal Sinuses

Paranasal sinuses
= air filled extensions of the respiratory part of the nasal cavity into the cranial bones (frontal, ethmoid, sphenoid, maxillary)
function:

• reduce weight of the skull
• warm, humidify and clean air
• help reverberate the voice

Frontal sinuses
- posterior to superciliary arches and root of nose
- detectable by age 7
- usually paired but rarely of equal sizes
separated by a non-median bony septum
- drains through the frontonasal duct into the ethmoidal infundibulum which opens into the semilunar hiatus of the middle nasal meatus
- innervated by supraorbital nerve (CN V1)
*keep in mind that the frontal sinuses are very variable*

Ethmoidal sinuses/cells
- small invaginations of the mucous membrane of the middle and superior nasal meatus
- between medial wall of orbit and nasal cavity (posterior and slightly inferior to frontal sinus)
- known as ethmoidal cells because of its cell-like structure (honeycomb)
- divided into 3 groups

• Anterior ethmoidal cells - drains into middle nasal meatus through the ethmoidal infundibulum
• Middle ethmoidal cells - also known as "Bullar cells" because forms the ethmoidal bulla (swelling on the superior border of semilunar hiatus), open directly into middle nasal meatus,
• Posterior ethmoidal cells - open directly into superior nasal meatus

- innervated by nasociliary nerve (CN V1)
*infection may break the fragile medial wall of the orbit, can cause blindness if severe*

Sphenoidal sinuses
- located in body of sphenoid
separated by a non-median bony septum
- derived from posterior ethmoidal cell at age of 2 years
- opens into sphenoethmoidal recess
- important structures close to it:

• nasal cavity anteriorly
• pituitary fossa and gland superiorly
• cavernous sinus laterally

- innervated by posterior ethmoidal nerve

Maxillary Sinuses
- largest paranasal sinus
- in the body of the maxilla
- apex - towards zygomatic bone
base - lateral wall of nasal cavity
roof - floor of orbit
floor - alveolar part of the maxilla
- drains into maxillary ostium into the middle nasal meatus via the semilunar hiatus
- innervated by superior alveolar nerves (CN V2)
Important things to note about maxillary sinus
1. Infection of the maxillary sinus is common becuase ostia are small and located high on their superomedial walls. Therefore often become obstructed. Also because of the location of the ostia, hard to drain unless it is full.
*Note that apparantly there is cilia present in the maxillary sinus which sweeps the fluid up into the nasal cavity - just like how your cilia sweeps the mucus in the respiratory tract. Fluid accumulates when the cilia fails to work like when there's infection and presence of pus*
2. 3 molar teeth - if removal is not done properly, fragments of the root of the teeth can pierce the sinus, causing infection. Inflammation of the sinus is often accompanied by toothache because supplied by superior alveolar nerves

Note: Important to know where the sinuses open into the nasal cavity

(Posted by: Vivian)