9. Nasal cavity and paranasal sinuses Flashcards
describe the components of the external nose
predominantly CARTILAGE but frontal processes of MAXILLAE and 2 NASAL BONES form its root
name the boundaries of the nasal cavity
- roof: frontal bone, cribiform plate of ethmoid and sphenoid
- floor: hard palate
- lateral walls: 2 superior conchae of ethmoid and inferior concha (own bone)
- medial wall: perpendicular plate of ethmoid, vomer and septal cartilage
name the openings of the nasal cavity
- anterior nasal apertures = nares/nostrils
- posterior nasal apertures = choanae
why does airflow slow in the nasal cavity
nasal cavity has greater cross-sectional area than nostrils/vestibule so air flow slows
what are the 2 types of mucous membrane in the nasal cavity, and describe their function
- olfactory mucous membrane (superiorly): olfaction - contains ends of CN I nerves
- respiratory mucous membrane: pseudostratified columnar ciliated epithelium for:
- filtering air (mucous/cilia)
- humidifying air (watery secretions)
- warming air (rich vascular supply)
what is the function of the conchae and meatuses
- chonchae: slow airflow by causing turbulence and increasing surface area over which air passes
- meatuses: paranasal sinus and lacrimal ducts drain here
how can trauma to nose cause ‘saddle-nose’ deformity
i. trauma causes buckling of nasal septum and shearing of blood vessels…
ii. blood accumulates between perichondrium and cartilage - septal haematoma…
iii. lifts perichrondrium off cartilage, stripping away its blood supply (avascular necrosis) and causing pressure necrosis from increased pressure by haematoma…
iv. irreversible cartilage necrosis - saddle-shape deformity
what are nasal polyps, describe symptoms
Common (>40yrs) benign swellings of nasal mucosa, usually bilateral.
Symptoms:
- blocked nose
- watery rhinorrhoea, post-nasal drip
- decreased smell and taste
(Unilateral polyp +/- blood-tinged secretion may suggest tumour)
describe the sensory innervation of the nasal cavity
General sensory: trigeminal n., mainly maxillary br. but also ophthalmic branch anteriorly
Special sensation: olfactory n.
describe the arterial supply to the nasal cavity
- anteriorly via greater and lesser branches of ethmoidal a. (from ophthalmic a.)
- posteriorly from sphenopalatine and greater palatine aa. (from maxillary a.)
- form arterial anastamoses in anterior septum (Keisselbach’s area)
from which vessels to epistaxis arise from - how does this affect treatment
- 90% from Keisselbach’s plexus: usually self-treated by pinching in front of bony bridge of nose and leaning head forwards
- 10% from sphenopalatine a.: can be more serious and difficult to treat as blood at high pressure and posteriorly located in nasal cavity.
- if initial management unsuccessful try:
i. cauterising visible bleeding point with silver nitrates
ii. anterior packing using nasal tampons
iii. posterior packing or surgical intervention as last resort
where does venous blood from nasal cavity drain to
facial v, pterygoid venous plexus, cavernous sinus
what are the paranasal sinuses and how do these relate to the nasal cavity
Air-filled spaces lined with respiratory mucosa (ciliated pseudostratified columnar with goblet cells) that are extensions of nasal cavity - drain into a meatus (mostly middle) via small ostia (channels). Help humidify and warm inspired air.
name the 4 different paranasal sinuses and state their innervation
- frontal (above eyes) - ophthalmic n. (CN Va)
- ethmoid air cells (medial to eyes) - ophthalmic n.
- sphenoid sinus (posterior to eyes) - ophthalmic n.
- maxillary (under eyes) - maxillary n. (CN Vb)
how can rhinitis (inflammation of nasal mucosa) cause sinusitis
Rhinitis causes decreased ciliary function, oedema of nasal mucosa and sinus ostia, and increased nasal secretions… impedes drainage from sinus… stagnant sinus secretions can be secondarily infected by bacteria
