Paranasal Sinuses

Question 1

General features of the nasal cavity

Answer 1

A. The nose is the proximal most portion of the respiratory tract; composed of external bony and cartilaginous nose and internal nasal cavities. Functions to warm, humidify, and filter air as it passes into the respiratory tract.

B. Paranasal sinuses are air-filled, epithelial-lined spaces inside the frontal, sphenoidal, ethmoidal, and maxillary bones; act to lighten the skull.

C. The paranasal sinuses form post-natally as the epithelial-lined spaces excavate through surrounding bone.

Question 2

Maxillary sinus

Answer 2

1. Within maxilla bone; largest of all air sinuses.
2. Relationships:
   a. Superior – orbit
   b. Medial – nasal cavity
   c. Inferior – maxillary teeth
   d. Anterior and lateral – cheek
   e. Posterior – pterygopalatine fossa
3. Drains to semilunar hiatus within middle nasal meatus.
4. Innervated by branches of V2

Question 3

Frontal sinus

Answer 3

1. Within frontal bone, superior to superciliary arches, nasal bones.
2. Relationships:
   a. Superior/Posterior – cranial cavity
   b. Inferior – nasal cavity/orbit
3. Open via frontonasal duct to semilunar hiatus within middle nasal meatus.
4. Innervated by V1

Question 4

Sphenoidal sinus

Answer 4

1. Within body of sphenoid bone
2. Relationships:
   a. Superior – cranial cavity
   b. Lateral – cavernous sinus/cranial cavity
   c. Anterior/inferior– nasopharynx/nasal cavity
3. Open to sphenoethmoidal recess
4. Innervated by V2

Question 5

Ethmoidal sinus

Answer 5

1. Within ethmoidal bone.
2. Anterior, middle, and posterior air cells.
3. Relationships:
   a. Superior – cranial cavity
   b. Medial/inferior – nasal cavity
   c. Lateral - orbit
4. Open via:
   a. semilunar hiatus of middle nasal meatus (anterior air cells).
   b. ethmoid bulla (middle air cells).
   c. superior nasal meatus (posterior air cells).
5. Innervated by V1

Question 6

E. CLINICAL CORRELATIONS: Sinusitis

Answer 6

1. Infection/inflammation of the paranasal sinuses.
2. Transillumination of the sinuses can be used to detect fluid levels within paranasal sinuses.
3. Can be complicated by spread to surrounding structures; i.e the eye and optic nerve (causing optic neuritis), teeth, brain/meninges.
4. Infections of maxillary teeth can also spread to maxillary air sinus.
5. Maxillary sinus is most susceptive to infection due to drainage. The ostia of maxillary sinuses are located on the upper wall of the sinus. Thus, fluid has to completely fill the sinus before it can drain.

Question 7

External nose

Answer 7

A. Nares – external openings

B. Composed of bony and cartilaginous structures

1. Nasal, maxilla, frontal bones
2. Nasal cartilages

Question 8

Nasal cavities: roof

Answer 8

a. Ethmoid bone (cribriform plate)
b. Frontal bone
c. Sphenoid bone

Question 9

nasal cavities: lateral wall

Answer 9

a. Ethmoid bone – superior and middle concha
b. Inferior concha
c. Maxilla bone
d. Palatine bone – perpendicular plate
e. Lacrimal bone

Question 10

nasal cavities: floor

Answer 10

a. Palatine bone

b. Maxilla bone

Question 11

nasal cavities: anterior wall

Answer 11

a. Nasal cartilages, nasal bones
b. Nares are the anterior openings to the nasal cavity; lead to skin lined vestibule which contains vibrissae, hair cells which filter incoming air.

Question 12

nasal cavities: posterior

Answer 12

open to nasopharynx via choanae

Question 13

nasal cavities: medial wall (nasal septum)

Answer 13

a. Perpendicular plate of ethmoid bone
b. Vomer bone
c. Nasal cartilages
d. CLINICAL CORRELATION – a deviated septum can sometimes be so severe that it affects breathing; deviation can be corrected surgically.

Question 14

Nasal mucosa

Answer 14

1. Respiratory epithelium lines bulk of nasal cavity; rich in blood vessels and mucous glands to warm air as it passes through the cavity.
2. Olfactory epithelium lines superior-posterior portion of cavity; contains CN I.

Question 15

CLINICAL CORRELATIONS: Rhinitis

Answer 15

inflammation of the nasal mucosa

2. Infection can spread to:
   a. Anterior cranial fossa via cribriform plate
   b. Nasopharynx
   c. Middle ear via pharyngotympanic tube
   d. Lacrimal apparatus and conjunctiva via nasolacrimal duct
   e. Paranasal sinuses

Question 16

Meatuses

Answer 16

1. Sphenoethmoidal recess
   a. Area posterior and superior to superior concha.
   b. Contains opening for sphenoidal sinus.
2. Superior
   a. Beneath superior concha
   b. Contains opening for posterior ethmoidal sinus.
3. Middle
   a. Beneath middle concha
   b. Contains bulla ethmoidalis and semilunar hiatus
   c. Contains openings for frontal, maxillary, anterior and middle ethmoidal sinuses.
4. Inferior
   a. Beneath inferior concha
   b. Contains opening for nasolacrimal duct

Question 17

Drainage of paranasal sinuses/nasolacrimal duct

Answer 17

1. Sphenoid sinus drains to sphenoethmoidal recess
2. Frontal sinus drains via frontonasal duct to semilunar hiatus within middle nasal meatus.
3. Maxillary sinus drains to semilunar hiatus within middle nasal meatus.
4. Ethmoidal air cells drain via:
   a. Anterior ethmoidal air cells to semilunar hiatus within middle nasal meatus.
   b. Middle ethmoidal air cells to ethmoid bulla within middle nasal meatus.
   c. Posterior ethmoidal air cells to superior nasal meatus
5. Nasolacrimal duct drains lacrimal fluid to inferior nasal meatus.

Question 18

Blood supply to paranasal sinuses: internal carotid portion

Answer 18

a. Anterior and posterior ethmoidal aa.
1. Branches of ophthalmic a.
2. Courses through ethmoidal air cells and enter roof of nasal cavity.
3. Provide lateral nasal and septal branches to nasal cavity
4. Provide ethmoid sinuses
5. Provide external nose (external nasal branch)

Question 19

Blood supply to paranasal sinuses: external carotid portion

Answer 19

a. Sphenopalatine a.
1. Terminal branch of maxillary a.
2. Enters nasal cavity posteriorly via the sphenopalatine foramen.
3. Provides posterior lateral nasal and septal branches
b. Greater palatine a
1. Branch of maxillary artery
2. Enters nasal cavity via incisive canal
3. Provides nasal septal branches
c. Facial a – Septal branches from superior labial a.

Question 20

Kiesselbach area

Answer 20

anastomoses between greater palatine, anterior ethmoidal, sphenopalatine, facial arteries on anterior portion of nasal septum.

Question 21

venous drainage of paranasal sinuses

Answer 21

submucosal venous plexus drains to maxillary, facial, and ophthalmic vv

Question 22

Innervation of paranasal sinuses

Answer 22

1. Olfactory Nerve – CN I

2. Ophthalmic n ((V1)

Question 23

Olfactory Nerve – CN I

Answer 23

a. SVA
b. Olfaction – the sensation of odors that results from the detection of odorous substances aerosolized in the environment.
c. The bipolar neurons that compose CN I are located in the superior portion of the nasal cavity epithelium.
d. The fiber processes of CN I pass through the cribriform plate of the ethmoid bone to synapse in the olfactory bulb of the brain.
e. The olfactory bulb is an extension of the forebrain (telencephalon); thus CN I synapses directly within the forebrain.

Question 24

2. Ophthalmic n ((V1)

Answer 24

a. The ophthalmic branch of CN V enters the orbit via the superior orbital fissure; several branches will then provide GSA innervation to the nose and sinuses (to the anterior portion of the nasal cavity; ethmoidal sinus, and frontal sinus).
b. Branches involved:
1. Supraorbital and supratrochlear provide the frontal sinus.
2. Posterior ethmoidal n provides the ethmoid sinus
3. Anterior ethmoidal n.
a. Provides branches to ethmoidal air cells
b. Septal branches to anterior nasal cavity
c. Lateral branches to anterior lateral wall of nasal cavity
d. External nasal branch to dorsum of nose

Question 25

Maxillary n (V2)

Answer 25

a. The maxillary branch of CN V enters the pterygopalatine fossa via foramen rotundum; several branches will then provide GSA innervation to the nose and sinuses (most of the nasal cavity; maxillary sinus, and sphenoid sinus). b. Branches involved: 1. Infraorbital n a. Provides innervation to maxillary sinus. b. Also supplies innervation to face, including lateral nose. 2. Posterior superior alveolar – will provide maxillary sinus 3. Pharyngeal n a. Courses through floor/medial wall of sphenoid sinus b. Will provide sphenoid sinus 4. Nasopalatine n. a. Enters nasal cavity via sphenopalatine foramen and will provide the majority of innervation to the nasal septum. b. Continues to hard palate via incisive foramen. 5. Posterior superior lateral nasal n. a. Will enter nasal cavity via sphenopalatine foramen b. Provides innervation to superior lateral nasal wall. 6. Posterior inferior lateral nasal n. a. Enters nasal cavity via unnamed foramen b. Provides innervation to inferior lateral nasal wall

Question 26

parasympathetic innervation to nasal cavities/ paranasal sinuses

Answer 26

1. Parasympathetic a. Preganglionic cell bodies – salivatory nucleus in brainstem b. Preganglionic fibers travel with facial n. c. Facial n provides greater petrosal branch which exits temporal bone via the hiatus for the greater petrosal n. d. Now in the middle cranial fossa, the greater petrosal nerve joins the deep petrosal nerve to form the nerve of the pterygoid canal. e. N. of pterygoid canal travels in pterygoid canal to the pterygopalatine fossa. f. Postganglionic cell bodies – pterygopalatine ganglion g. Postganglionic fibers travel with branches of V2 to distribute to the nasal cavities and paranasal sinuses.

Question 27

sympathetic innervation to nasal cavities/ paranasal sinuses

Answer 27

a. Preganglionic cell bodies – T1-T4 b. Postganglionic cell bodies – superior cervical ganglion c. Postganglionic fibers form the internal carotid nerve → deep petrosal n. d. Deep and greater petrosal nerve form nerve of the pterygoid canal. e. Postganglionic fibers travel with branches of V2 to distribute to the nasal cavities and paranasal sinuses.

Question 28

lymphatic drainage of nasal cavities

Answer 28

1. Anterior portion drains along face to submandibular lymph nodes. 2. Posterior portion drains along pharynx to retropharyngeal lymph nodes.