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ANATOMY OF THE NOSE AND PARANASAL SINUSES
e sphenoid sinuses can also pneumatise laterally into the pterygoid root resulting in the
presence of a lateral sphenoid recess and exposure of the neurovascular structures surrounding the sphenoid sinus.
At birth, the frontal sinus is a small pocket. It is the last sinus to develop, and only seen
in most radiological studies by the age of 8 years, with signicant pneumatisation occurring in early adolescence. It remains hypoplastic or aplastic in approximately 10% of the
population
Anatomy of the Nose and Paranasal Sinuses
Skin and Muscles of the External Nose
e thickness of the skin and so tissues of the nasal bridge vary according to individual
skin type and anatomical location. Over the dorsum and sides of the nose, the nasal skin is
thin and loosely adherent to the underlying framework. e nasal skin becomes thicker and
more adherent toward the nasal tip and alar cartilages where it contains numerous sebaceous
glands. e elasticity and mobility of the skin over the nose also varies according to the quality of the collagen bers anchoring the skin to the underlying structures.
e supercial musculoaponeurotic system (SMAS) provides a vascular rich covering to
the underlying skeleton from superior labial and facial artery branches and corresponding
venous and lymphatic vessels. Its function is to compress, dilate, depress or elevate the nostrils and nasal tip. ese muscles are all supplied by branches of the facial nerve. e nasal
elevators include the procerus, levator labii superioris alaeque nasi and anomalous nasi muscles. e depressors include the alar nasalis and depressor septi nasi muscles. Compressor
muscles include the transverse nasalis and compressor narium minor. e dilator naris anterior muscle acts as a minor dilator.
e subcutaneous tissue of the nose is made up of four layers: supercial fatty, bromuscular, deep fatty and periosteal layers. e supercial fatty layer is directly connected to the
dermis. e bromuscular layer comprises the nasal SMAS. e deep fatty layer lies deep to
the SMAS and contains the neurovascular system. e deepest layer is the periosteum and
perichondrium. During external approach rhinoplasty, dissection deep to the third layer
(deep fatty tissue) minimises post-operative scarring and retraction because the neurovascular and SMAS structures are preserved.
Anatomical subunits of the nose are divided into thirds (Figure 25.1):
Upper (nasal bones, articulating the frontal processes of maxilla and bony septum)
•
Middle (‘vault’) (paired upper lateral cartilages (ULCs) inserting under the caudal end
•
of the nasal bones and their fusion with the midline cartilaginous septum)
Lower (from caudal edges of the ULCs to cephalic edge of lower lateral cartilages [LLCs])
•
Vestibule
e nasal vestibule is the anterior most aspect of the nasal cavity and serves as the entry point
from the external nares into the nasal cavity. e vestibule is demarcated by the limen nasi
located at the caudal border of the LLC. e limen nasi is the location where the marginal
incision is made during external approach rhinoplasty. It is important to note that only a
small part of the alar rim is composed of cartilage from the lateral crus of the LLC; the
majority is composed of brofatty tissue.
Nasal Cartilages
e LLC is divided into medial, intermediate and lateral crus that form the nasal ala arch.
Medial crural footplates extend to the lower columella, anterior to the caudal septum. e
nasal tip consists of paired LLCs. Within the intermediate crus lie the domes and tip-dening
points.
e ULCs attach to the dorsal septum in the midline, nasal bones cranially at the rhinion
and LLCs caudally via the scroll area.
138 Rhinology and Facial Plastic Surgery
ANATOMY OF THE NOSE AND PARANASAL SINUSES
Figure 25.1 (a) Lateral view demonstrating the constituents of the anatomical subunits of the
nose. (b) 1. Nasal bone. 2. Frontal process of the maxillary bone. 3. Upper lateral cartilage. 4. Area
of overlap of upper lateral cartilage by nasal bone. 5. Lateral crus of the lower lateral cartilage. 6.
Dome area within intermediate crus. 7. Medial crus of the lower lateral cartilage. 8. Quadrilateral
cartilage. 9. Connective tissue. 10. Scroll region. 11. Shaded area showing removed nasal bone.
(Reproduced with permission from Anatomy. RML Poublon In Rhinoplasty; A Practical Guide to
Functional and Aesthetic Surgery of the Nose. 1993 Amsterdam/New York. Kugler publications.)
e LLCs and their combined support contribute to the concept of the ‘tripod’. e brous
connection between the medial crura of the LLC are considered one leg of the tripod, with
the lateral crura of the LLC forming the other two legs (Figure 25.2). e tripod mechanism
plays a dynamic role in the cantilevering of the nasal tip in cosmetic rhinoplasty.
Figure 25.2 Tripod complex of the lower third of the nose. The conjoint medial crura comprise
one leg of the tripod, while the lateral crura comprise the other two legs.
Rhinology and Facial Plastic Surgery 139
ANATOMY OF THE NOSE AND PARANASAL SINUSES
Figure 25.3 Nasal valves. (A) Midline sagittal computed tomography scan with green line indi-
cating the relative positions of the external (e) and internal (i) nasal valves. (T) represents brain
parenchyma and (B) base of tongue.(B) Endoscopic view of the left external nasal valve comprised
of the (1) septum medially, (2) alar rim laterally (comprised of lower lateral crus, sesamoid complex
and brofatty tissue) and (3) nasal sill inferiorly. (C) Endoscopic view of the left internal nasal valve
comprised of the (1) septum medially, (2) caudal edge of upper lateral cartilage and (3) head of
inferior turbinate laterally and nasal oor inferiorly.
Nasal Valve
e LLC and ULC form the external and internal nasal valves, which are critical to
nasal airow. Boundaries of both external and internal valve are depicted in Figure 25.3.
Anatomical abnormalities of external nasal valve or compromise in its structural integrity can cause narrowing, stenosis or dynamic valve collapse that is exacerbated during
inspiration.
e internal nasal valve is the narrowest portion of the nasal cavity. e apex of the internal
nasal valve is approximately 10–15 degrees in Caucasians and wider in non-Caucasian populations. Changes in the relationship of any structure within this space can cause symptoms
of nasal obstruction.
Nasal Septum
e nasal septum consists of the following structures (Figure 25.4):
Bone (comprised of the perpendicular plate of the ethmoid bone, vomer, maxillary
•
crest and palatine bone)
Cartilage (composed of the quadrilateral cartilage)
•
Membranous portions (segment of connective tissue between the caudal septal carti-
•
lage and columella)
e inferior attachment of the cartilaginous portion sits within the nasal crest of the maxilla
and is bound by looser connective tissue creating a pseudoarthrosis, reducing risk of traumatic fracture or dislocation.
Lateral Nasal Wall and Turbinates
The middle and superior turbinate arise from the ethmoid bone. The inferior turbinate
is an embryologically independent osseus structure. The space between the turbinates is
the meatus, which is associated with well-defined drainage pathways. This three-dimensional area is often referred to as the hiatus semilunaris, which is a crescent-shaped
groove in the lateral wall of the nasal cavity just inferior to the ethmoidal bulla. It is the
location of the openings for the frontal sinus, maxillary sinus and anterior ethmoidal
sinus (Figure 25.5).
e lacrimal duct drains into the inferior meatus approximately 1cm posterior to the inferior
turbinate head by an opening called Hasner’s valve. e middle and superior meatuses and
sphenoethmoid recess will be discussed later.
140 Rhinology and Facial Plastic Surgery
ANATOMY OF THE NOSE AND PARANASAL SINUSES
Septal branch of
palatine
Sphenopalatine
Figure 25.4 The cartilaginous and bony components of the nasal septum. Nasal septum. A – Nasal
process of frontal bone. B – Perpendicular plate of ethmoid. C – Nasal bones. D – Vomer. E – Horizontal
plate of palatine bone. F – Palatine process of maxillary bone. G – Anterior nasal spine. H – Quadrangular
cartilage. I – Upper lateral cartilage. J – membranous part of septum. K – Alar cartilage.
Kisselbach’s
plexus
superiorlabial
Anterior
ethmoid
Septal branch of
greater palatine
Posterior
ethmoid
Septal branch of
spheno-palatine
Anterior
ethmoid
Posterior
ethmoid
Greater
Figure 25.5 Vascular supply of (A) nasal septum and (B) lateral nasal wall.
Blood Supply of External Nose
Branches of the facial artery (angular and superior labial arteries) supply the alar region.
e nasal side wall and dorsum also receive supply from the ophthalmic, infra-orbital and
external branch of the anterior ethmoid arteries.
Venous networks do not parallel the arterial supply but correspond to territories. e upper
lip and nose are considered the danger area of the face because infections in this region may
be transmitted retrograde to the cavernous sinus through the valveless ophthalmic vein.
Blood Supply of Nasal Cavity
e sphenopalatine artery is the major contributing artery (Fig ure 25.3). It enters through the
sphenopalatine foramen inferior to the middle turbinate horizontal attachment. e crista
Rhinology and Facial Plastic Surgery 141
ANATOMY OF THE NOSE AND PARANASAL SINUSES
ethmoidalis is a small crest of palatine bone located anterior to sphenopalatine foramen
serving as a consistent surgical landmark.
e anterior ethmoid artery, posterior septal artery (branch of sphenopalatine artery) and
septal branch of superior labial artery contribute to Kiesselbach’s plexus along the anterior
septum at Little’s area (Figure 25.3). is is a common location of epistaxis due to its rich
vascular supply, and it is susceptible to injury from turbulent airow and digital trauma.
Internal carotid artery contribution occurs via anterior and posterior ethmoid arteries
(branches of ophthalmic artery). e anterior ethmoid artery traverses three compartments
of the head during its course from the orbit between the superior oblique and medial rectus muscle, through the ethmoid cavity either within skull base bone or a mucosal mesentery, and enters through the lateral lamella of the lamina cribrosa into the olfactory fossa
intracranially.
Functional Anatomy of the Paranasal Sinuses
e paranasal sinuses are divided into functional units based on drainage pathways:
Anterior unit (maxillary, anterior ethmoid and frontal sinuses draining into ostiome-
•
atal complex, lateral to the middle turbinate)
Posterior unit (posterior ethmoid and sphenoid sinus drain into superior meatus)
•
Sphenoid compartments (sphenoid sinus draining into sphenoethmoid recess)
•
Details of anatomy for each unit are depicted in Figure 25.5.
Anterior Functional Unit
Uncinate Process and Maxillary Sinus
e uncinate process is a sickle-shaped bone which attaches inferiorly to the inferior turbinate and palatine bone, and anterosuperiorly to the lacrimal bone. e uncinate, together
with a fold of mucosa called the anterior and posterior fontanelle, cover the opening to the
maxillary sinus. Accessory ostia may be present in the fontanelle that can be mistaken for
the true maxillary ostium. Failure to correctly identify the true ostia and connect it with the
common sinus cavity may result in a phenomenon known as mucous recirculation. During
recirculation, mucuus is directed towards the natural opening along the mucociliary drainage pathway and re-enters the sinus through the accessory ostium.
Ethmoid Bulla
e ethmoid bulla is the largest and most consistent anterior ethmoid air cell. It attaches
to the lamina papyracea laterally and has variable attachments to the skull base and basal
lamella creating a series of cles and spaces that are well described.
ethmoid cell can pneumatise into the maxillary sinus as a normal variant called a Haller cell.
Middle Turbinate
e complex shape of the middle turbinate is divided into three segments:
Sagittal (attaches to the skull base at the lateral lamella)
•
Coronal (basal lamella which separates anterior and posterior ethmoid cavities)
•
Axial (attaches to the lateral nasal wall at the sphenopalatine artery terminal branch
•
point)
Frontal Sinus
To dene the limits of the frontal sinus recess, one must consider structures that may
encroach this space:
Anteriorly (agger nasi, posterosuperior uncinate process and frontal ethmoid cells)
•
Posteriorly (supraorbital ethmoid and suprabulla cells)
•
Medially and latera l directions (intersinus septal cel ls and a medially inserting uncinate)
•
142 Rhinology and Facial Plastic Surgery
1
An infra-orbital anterior
ANATOMY OF THE NOSE AND PARANASAL SINUSES
Agger nasi is the anterior-most ethmoid cell and its medial border is formed by the uncinate
process. e degree of agger pneumatisation inuences the superior uncinate position and
nasofrontal beak thickness.
e uncinate process can insert into the medial orbital wall, skull base or middle turbinate and has multiple attachments in more than 50% of cases. e uncinate inserts into the
medial orbital wall in 85% of cases resulting in a frontal recess drainage pathway medial to
the uncinate. An uncinate with an isolated attachment to the skull base or middle turbinate
occurs in 15% of cases leading to drainage lateral to the uncinate.
Frontal ethmoid cells pneumatise above the agger towards the frontal sinus. e Wormald
classication describes four congurations:
Type 1 (single frontal ethmoidal cell above the agger nasi and below the frontal sinus
•
oor)
Type 2 (tier of cells above the agger nasi)
•
Type 3 (cells that ll less than 50% of the frontal sinus)
•
Type 4 (cells ll greater than 50% of the frontal sinus)
•
Supraorbital ethmoid cells are anterior ethmoid cells extending superiorly and laterally over
the orbital roof. Suprabulla cells are pneumatised extensions above the ethmoid bulla up the
skull base and frontal sinus posterior table.
Medial structures encroaching on the frontal recess include intersinus septal cells and a
medially inserting uncinate. Intersinus septal cells represent pneumatisation of the frontal
sinus septum. Lateral encroaching structures include frontal cells, agger nasi and a lateral
uncinate attachment.
Posterior Functional Unit
e posterior functional unit is comprised of the posterior ethmoid cells which drain into
the superior meatus. An Onodi cell is a posterior ethmoid cell that pneumatises laterally and
posteriorly over the optic nerve exposing it to injury during surgery.
Sphenoid Functional Unit
e sphenoid functional unit is comprised of the sphenoid sinus which drains into the sphenoethmoid recess between the superior meatus and septum. e supreme turbinate may be
seen here. e sphenoid ostium opens behind the superior turbinate. Structures associated
with the sphenoid sinus include the optic nerve, carotid artery and sella turcica.
KEY POINTS
• Identify key xed anatomical landmarks to delineate the limits of dissection of the
paranasal sinus surgical cavity (box) for safe and complete endoscopic sinus surgery.
• The main structures are the orbit and skull base. These are dened by the (1) maxillary
sinus roof (orbital oor), (2) medial orbital wall, (3) sphenoid sinus roof (skull base) and
(4) the lateral sphenoid wall (orbital apex).
• Paranasal sinuses are divided into anterior, posterior and sphenoid compartments
that serve as functional units based on mucociliary drainage pathways. Once a
compartment is surgically entered, all mucosal cells within the compartment must be
completely dissected to create a new functional neo-sinus cavity.
Further Reading
1. Stammberger HR, Kennedy DW, Anatomic terminology group. Paranasal sinuses: anatomic terminology and nomenclature. Ann Otol Rhinol Laryngol Suppl 1995; 167: 7–16.
2. Kew J, Rees GL, Close D, et al. Multiplanar reconstructed computed tomography
images improves depiction and understanding of the anatomy of the frontal sinus and
recess. Am J Rhinol 2002; 16(2): 119–23.
Rhinology and Facial Plastic Surgery 143
Lateral nasal wall.
ANATOMY OF THE NOSE AND PARANASAL SINUSES
Lateral nasal wall with middle turbinate reected posteriorly exposing the middle meatal complex.
Lateral nasal wall with middle turbinate removed illustrating the basal lamella (BL) separating the
ethmoid bulla (EB) from the posterior ethmoid cells (PE). FR – to frontal recess. AC – Agger nasi cell.
144 Rhinology and Facial Plastic Surgery
PHYSIOLOGY OF THE NOSE AND PARANASAL SINUSES
26. PHYSIOLOGY OF THE NOSE AND PARANASAL SINUSES
Introduction
e nose is a complex organ that forms an important part of the face and has multiple
functions.
Respiratory functions include heat exchange, ltration, humidication, nasal neurovascular reexes and voice modication. e nose also serves as a sense organ, housing the
olfactory apparatus that allows individuals to smell substances for pleasure and defence
purposes.
e physiological role of the paranasal sinuses is uncertain, but several possible functions
have been suggested including:
Physical buer against injury to face
•
Vocal resonance
•
Reduction of skull weight
•
Heat insulation
•
Humidication
•
Air conditioning
•
Nasal Blood Flow
e nasal mucosa is very vascular containing arterioles, arteriovenous anastomoses and
venous sinusoids, with a large surface area of 150 cm2. ey can expand and shrink, which
has an impact on the nasal resistance and nasal airow. Inferior turbinate has erectile tissue and a rich blood supply, increasing interaction of inspired air with nasal mucosa. If the
mucosal thickness increases by 1–2 mm, nasal ow velocity signicantly decreases, from
0.89–0.42 m/s in the normal nose.
Autonomic Nervous System
e autonomic nervous system controls the activity of smooth muscle found in the walls
of the arteriovenous anastomoses leading to changes in nasal blood ow. Parasympathetic
bres travel via the maxillary branch of the trigeminal nerve (CN V2) to provide secretomotor supply to the mucous glands in the nasal cavity. Sympathetic bres predominantly innervate smooth muscle in the walls of arterioles and sinusoids. Drugs may mimic the eects of
the sympathetic and parasympathetic nerve supply (Table 26.1).
Epithelium-Ciliary Function
ere are three types of epithelium in the nose:
1 Stratied squamous epithelium covering nasal vestibule containing vibrissae, sweat
glands.
2 Pseudostratied ciliated columnar epithelium covers the majority of the nasal cavity
and contains ciliated and non-ciliated columnar cells, mucin-secreting goblet cells
and basal cells.
3 Olfactory neuroepithelium is located along the upper one-third of septum, medial
superior/supreme turbinates and roof of nasal cavity.
Defence Mechanisms of the Nasal Mucosa
e nose has a role in protective mechanisms to prevent noxious substances from entering the lower respiratory tract, which can be divided into mechanical and immunological
defence.
Rhinology and Facial Plastic Surgery 145
PHYSIOLOGY OF THE NOSE AND PARANASAL SINUSES
Table 26.1 Drugs acting on the nasal mucosa
Drug group Mode of action Example
Sympathomimetics Compounds act on alpha-1
receptors and cause
vasoconstriction, reducing
nasal congestion
Parasympathomimetics Compounds act to cause
vasodilation and increase
nasal secretions
Antihistamines Predominantly block H1
receptors Histamine is found
mainly in mast cells and
causes vasodilation and
increases plasma leaking
from capillaries
Local anaesthetics Inhibit Na channel inux
therefore reduce the rate of
depolarisation/repolarisation
Adrenaline, noradrenaline,
xylometazoline (Otrivine)
Cocaine blocks uptake of
noradrenaline in nerve endings;
also acts as a local anaesthetic
Antagonist: Alpha blockers e.g.
doxazosin for hypertension
Pilocarpine causes vasodilation and
watery secretions
Antagonists: Ipratropium bromide
blocks muscarinic receptors, thus
preventing acetylcholine from
binding
Antihistamines
Lignocaine
Mechanical Defence e nose can protect the lower airway by removing particles of
approximately 30 μm or upward such as pollen in inspired air (mechanical defence). e
velocity of the inspired air drops signicantly aer the nasal valve. Supercial viscous layer
produced by goblet cells traps particles. e columnar epithelial cells with specialised ciliary modications produce a rowing-like action and push particles entrapped in mucous
backwards into the nasopharynx.
Each cilium is composed of a bundle of interconnected microtubules beating 10–20 times
per second. Dry conditions, hyper- (>5%) or hypotonic (<2%) saline solutions, temperatures
below 10°C and temperatures above 45°C can stop ciliary movements. Infections in the upper
respiratory tract can cause damage to the epithelium, and the function of cilia also deteriorate
with age. Smoking causes a reduction in the number of cilia and change in mucous viscosity.
Immunological Defence Mucous consists of compounds that can neutralise anti-
gens through innate mechanisms and learned and adaptive immunological responses.
Immunoglobulin A (IgA) and IgE are found on the surface, and they act whenever the
mucosa is breached.
Nasal Aerodynamics
Nasal ow is laminar as it enters the vestibule. Increased resistance at the nasal valve area,
the narrowest part of the upper respiratory tract, leads to a drop of airow velocity.
e velocity of air increases as it passes the nasal valve, the narrowest part of the upper
respiratory tract (Figure 26.1). With change of velocity, laminar ow turns into a turbulent
ow, which results in reduced air velocity and prolonged contact of inspired air with the
nasal mucosa, allowing the nose to perform its vital functions. Normally, 50% of air ows
via the middle meatus. Septal deviations and turbinate hypertrophy may increase resistance
and cause nasal obstruction. However, when resistance is too low, patients may suer with
paradoxical obstruction known as ‘empty nose syndrome’.
146 Rhinology and Facial Plastic Surgery
PHYSIOLOGY OF THE NOSE AND PARANASAL SINUSES
Velocity
(Streamline 1)
5.700e + 000
4.277e+000
2.855e+000
1.432e+000
1.000e–002
–1
]
[ms
Figure 26.1 Velocity streamlines. Fluid dynamic experiments of the nose have shown that nasal
ow is laminar as it enters the vestibule, with no mixing of the different air layers at low velocity.
Nasal Cycle
e nasal cycle is a physiological process during which each side of the nose alternates
between congestion and decongestion. Changes are cyclical, occurring every 4–12 hours and
are present in 80% of adults, although dicult to demonstrate in children. Nasal cycle is
operated by the autonomic nervous system, which regulates constriction of the arterioles,
precapillary sphincters and venous sinusoids within the erectile mucosa. Amplitude of nasal
cycle may be inuenced by exercise, pregnancy, hormones, congestion, allergy, fear, emotions and sexual activity.
KEY POINTS
• The principal physiological function of the nose is to
• humidify and warm inspired air
• remove noxious particles from the air
• serves as a sense organ
• The nose has an abundant blood supply, from branches of both the internal and
external carotid arteries.
• The venous sinuses form the erectile tissue that is located on the anterior nasal septum
and the inferior turbinates.
• Smoking causes a reduction in the number of cilia and change in mucous viscosity.
• The nasal cycle is a well-recognised physiological activity whereby each side of the
nose alternates the phases of congestion and decongestion.
• Nasal resistance plays a crucial role in preventing the collapse of the lower respiratory
tract, notably the lungs, with nasal resistance contributing to up to 50% of the total
airway resistance.
Rhinology and Facial Plastic Surgery 147
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