Nasal Cavity And Cranial Senses

Question 1

Describe the projection of paranasal sinus onto the skull

Answer 1

• Theparanasalsinusesareair-filled cavities that reduce the weight of the skull
• Subject to inflammation that may cause pain over the affected sinus (e.g., frontal headache due to frontal sinusitis)
• Knowing the location of the sinuses is helpful in making the correct diagnosis

Question 2

What lines the interior of each sinus?

Answer 2

The interior of each sinus in lined with ciliated pseudostratified columnar epithelium with goblet cells (respiratory epithelium)

Question 3

What is the central structure of the paranasal sinuses?

Answer 3

The central structure of the paranasal sinuses is the ethmoid bone (red). Its cribriform plate forms a portion of the anterior skull base. The frontal and maxillary sinuses are grouped around the ethmoid bone. In the nasal cavity, the inferior, middle and superior nasal meatuses are visible. They are each bounded by their analogously-named concha.

The middle concha is a useful landmark in surgical procedures on the anterior ethmoid bone and the maxillary sinus, the bony ostium of which is located lateral to the middle concha, and opens into the middle meatus. Below this concha, located cranially is the largest chamber in the ethmoid bone, the ethmoidal bullae. At its anterior margin a bony hook is visible. It bounds the maxillary sinus opening anteriorly as the uncinate process.

The lateral wall separating the ethmoid bone from the orbit is paper-thin (lamina papyracea) so inflammatory processes and tumors may penetrate this thin plate in either direction.

Note: The deepest point of the maxillary sinus is in the root area of the maxillary molars (in 30% of people, the distance between maxillary sinus and buccal root is less than 1 mm). Thus, periapical inflammation in this area can extend to the sinus floor. When extracting an upper molar, opening the maxillary sinus is a possibility.

The transverse section, shows the hypophysis, located behind the sphenoid sinus in the hypophyseal fossa, is accessible to trans-nasal surgical procedures. The surface of the mucosa has been left intact to show how narrow the entire nasal cavity is and how swelling can quickly obstruct it

Question 4

Describe the mucosa of the nasal cavity

Answer 4

While the medial wall of the nasal cavity is smooth, its lateral wall is raised into folds by the three conchae (superior, middle, and inferior concha)

These increase the surface area of the nasal cavity, enabling it to warm and humidify the inspired air more efficiently

Question 5

What bones make up the lateral wall of the nasal cavity?

Answer 5

Sphenoethmoidal recess
• Sphenoid sinus

• Superior meatus
  * Posterior ethmoid cells
• Middle meatus
  
  • Frontal sinus
  • Maxillary sinus
  • Anterior ethmoid cells
  • Middle ethmoid cells
• Inferior meatus
• Nasolacrimal duct

Question 6

What make up the walls of the nasal cavity?

Answer 6

The nasal cavity has four walls
• Roof
• nasal, frontal, ethmoid

* floor * maxilla, palatine     * lateral wall * maxilla, nasal, lacrimal, ethmoid, palatine, inferior concha

• medial wall
  
  • nasal septum
    
    • ethmoid, vomer
    • nasal, sphenoid, palatine, maxilla (contributing only small bony projections to the nasal septum)

Question 7

What major arteries supply the lateral nasal cavity?

Answer 7

Note the vascular supply from the branches of the internal carotid artery (from above) and the
external carotid artery (from behind).

Question 8

What nerves of the lateral wall of the nasal cavity?

Answer 8

• The lateral nasal wall derives its sensory innervation from branches of the ophthalmic division (CN V1) and the maxillary division (CN V2 of the trigeminal n.).
• Receptor neurons in the olfactory mucosa send their axons in the olfactory nerve (CN I) to the olfactory bulb.

Question 9

What are the nerves of the nasal septum?

Answer 9

Sensory innervation from branches of the trigeminal nerve (CN V).
• Anterosuperior part of the septum is supplied by branches of the ophthalmic division (CN V1)
• Rest by branches of the maxillary division (CN V2).
• Bundles of olfactory nerve fibers (CN I) arise from receptors in the olfactory mucosa.

Question 10

What is Kiessselbachs area?

Answer 10

Nosebleeds:
Vascular supply to the nasal cavity arises from both the internal and external carotid arteries.

The anterior part of the nasal septum contains a very vascularized region referred to as Kiesselbach’s area.

This area is the most common site of significant nosebleeds.

Question 11

Describe the lymphatic drainage of the nasal cavity

Answer 11

• The external nose and cavity drains into 2 groups of nodes
  
  • Submandibular nodes
  • Pre-auricular and parotid nodes
  • Some lymph from the posterior portion of the cavity may pass to the retropharyngeal nodes

• These all drain into the deep cervical nodes along the internal jugular vein

• Receives all lymph from the head and neck
  
  • 2 distinct nodes
  • Jugulodigastric node
  • Jugulo-omohyoid node

Question 12

What nerves control the gag reflex?

Answer 12

The gag reflex
Afferent limb (sensation from the pharynx) – CN IX 

Efferent limb (motor response of the pharynx) – CN X

Question 13

What is the function of the tonsils fossa?

Answer 13

• The tonsillar fossa which houses the palatine tonsil has within its walls CN IX which provides general sensation and special sensory fibers to the posterior 1/3 of the tongue as well as general sensation to oropharynx
• The blood supply to the tonsil is mainly from the tonsillar branch of facial artery

Question 14

Describe lymphatic drainage of the nasal cavity

Answer 14

Deep cervical Nodes
All lymph from head and neck region will drain here eventually

Jugulodigastric-at point where digastruc crosses IJV

Jugular-omohyoid- at omohyoid junction

Pre-auricular

Parotid

Submandibular

Submental

Drains superficial and deep portions 9f anterior face

Question 15

What’s the significance if the obligate nasal breathers?

Answer 15

Newborns are obligate nasal breathers, they ‘refuse’ to breathe through the mouth if it is not necessary. Choanal atresia in a newborn thus needs an oral airway for the baby in the first instance before other treatment.

Smelling salt is a misnomer as it is an irritant to the nasal lining, it irritates CN V. It may have a scent but that is not the ‘painful’ stimulus.

Ethmoid bone has many parts like the cribriform plate and the perpendicular plate of the ethmoid as part of the nasal septum.

Operation that involves the nasal cavity, for instance removal of nasal polyps, must be clear of the cribriform plate to avoid severing the plate which would lead to problems with CN I (smell) and possible CSF leak leading to infection-meningitis-brain abscess.

Septal repair operations must make sure not to mobilize the septum to avoid problems with the cribriform plate. Hence the instruments used are usually punch to avoid motion of the septum

Question 16

How can COVID 19 cause loss of smell?

Answer 16

Loss of smell: consider Influenza infection in the past, COVID-19, meningioma in the anterior cranial fossa (space occupying lesion).

Swelling in the nose that originates from the midline may be a septal hematoma. A swelling ‘dangling’ in the center may be a nasal polyp and has no sensation. A swelling originating from the lateral side is most likely originating from an enlarged, swollen mucosal lining of the inferior concha and middle concha (related to allergies or overuse of decongestants).

Since CT scans are done frequently and certain bony structures are ‘unique’ those images can be assisting in forensic investigations. Frontal sinuses are not symmetrical and the septum between left and right can be way off the midline and could be characteristic for an individual.

Function of the sinuses: weight (minimal), vestigial smell organ, warming of air, NO production, growth related-expansion of the skull. Many reasons given, no clear answer. But as a physician-surgeon you make use of them.

Fracture of the floor of the orbit can be approached through the inferior meatus leaving a catheter behind temporarily which when inflated supports the roof until healed

Question 17

What’s the significance of nasal cilia?

Answer 17

Cilia of the nasal lining is towards the natural opening of the sinus. Regardless of making an accessory opening in the maxillary sinus, the cilia are still beating towards the natural opening.

What a second opening accomplishes is the principle of opening a can of juice: pouring is so much easier because no vacuum is build up by the second opening.

Know your coronal slide of the bony structure of the paranasal sinuses because it shows you the possible route of an expanding tumor.

Question 18

What is sphenopalatine used for?

Answer 18

• Sphenopalatine block for headaches, but also a perfect way of numbing most of the major nerves to the nasal structures and when used with a vasoconstrictor, producing a bloodless field for intra nasal operations under local anesthesia.
• Massive epistaxis: one of the methods is to clip the ethmoid arteries that supply the nose (branches of ICA), and ligation of the ECA which also supplies the nose.