Embryology and Anatomy of external nose

1. EMBRYOLOGY &
ANATOMY OF
EXTERNAL NOSE
DR/ AHLAM ALZUWAY

2. History of Rhinology

3. Embryology of the nose
In the early development of the embryo, neural crest cells migrate to form the mesenchymal
tissue as ectomesenchyme of the pharyngeal arches.
By the end of the 4th wk, the 1st pair of pharyngeal arches form 5 facial prominences or
processes an unpaired frontonasal process, paired mandibular processes and paired maxillary
processes.
The nose is largely formed by the fusion of these five facial prominences.
The frontonasal process gives rise to the bridge of the nose.
The medial nasal processes provide the crest and the tip of the nose, and the lateral nasal
processes form the alae or sides of the nose.
The frontonasal process is a proliferation of mesenchyme in front of the brain vesicles, and
makes up the upper border of the stomadeum.

4. -In the 5th wk ,the maxillary processes increase in size and at the same time the ectoderm
of the frontonasal process becomes thickened at its sides and also increases in size, forming the
nasal placodes.
The nasal placodes are also known as the olfactory placodes.
This development is induced by the ventral part of the forebrain.
In the 6th wk the ectoderm in each nasal placode invaginates to form an indented oval-shaped
pit, which forms a surrounding raised ridge of tissue. Each nasal pit forms a division between
the ridges, into a lateral nasal process on the outer edge, and a medial nasal process on the
inner edge.
During the 6th wk the nasal pits deepen as they penetrate into the underlying mesenchyme. At
this time, the medial nasal processes migrate towards each other and fuse forming the
primordium of the bridge of the nose and the septum.

5. The migration is helped by the increased growth of the maxillary prominences medially, which
compresses the medial nasal processes towards the midline.
Their merging takes place at the surface, and also at a deeper level.
The merge forms the intermaxillary segment, and this is continuous with the rostral part of the
nasal septum.
The tips of the maxillary processes also grow and fuse with the intermaxillary process. The
intermaxillary process gives rise to the philtrum of the upper lip.

7. At the end of 6th wk the nasal pits have deepened and fuse to make a large ectodermal nasal sac. This sac will be
above and to the back of the intermaxillary process.
7th wk, the nasal sac floor and posterior wall grow to form a thickened plate-like ectodermal structure called the
nasal fin. The nasal fin separates the sac from the oral cavity.
Within the fin, vacuoles develop that fuse with the nasal sac. This enlarges the nasal sac and at the same time
thins the fin to a membrane - the oronasal membrane that separates the nasal pits from the oral cavity. During
the7th wk the oronasal membrane ruptures to form an opening - the single primitive choana. The intermaxillary
segment extends posteriorly to form the primary palate which makes up the floor of the nasal cavity.
During the 8th &9th wks a pair of thin extensions form from the medial walls of the maxillary process. These
extensions are called the palatine shelves that form the secondary palate. The secondary palate will
endochondrally ossify to form the hard palate - the end-stage floor of the nasal cavity. During this time ectoderm
and mesoderm of the frontonasal process produce the midline septum.
The septum grows down from the roof of the nasal cavity and fuses with the developing palates along the
midline. The septum divides the nasal cavity into two nasal passages opening into the pharynx through the
definitive choanae.

8. At 10th wk, the cells differentiate into muscle, cartilage, and bone. Problems at this stage of
development can cause birth defects such as choanal atresia, facial clefts and nasal dysplasia or
extremely rarely polyrrhinia the formation of a duplicate nose.
Normal development is critical because the newborn infant breathes through the nose for the
first six weeks, and any nasal blockage will need emergency treatment to clear.

10. External nasal anatomy
Subcutaneous layers of the nose
(a) Superficial fatty layer (connected to dermis)
(b) Fibromuscular layer (nasal superficial musculoaponeurotic system)
(c) Deep fatty layers (contains neurovascular system)
(d) Periosteum/perichondrium
Optimal plane of dissection is located between (c) and (d) as it is avascular
and heals with minimal fibrosis

11. Nasal osteology:
(a) Two nasal bones fuse in the midline to form a pyramidal shape
(b) Nasal bones are thicker superiorly than inferiorly
(c) Nasal bone attachments:
-Superior: nasal process of frontal bone
- Lateral: frontal process of maxilla
(d) Pyriform aperture :
bony opening into the nasal cavity bounded by
-Superior: caudal margin of nasal bones
-Inferior: alveolar process of maxilla
-Lateral: frontal process of maxilla
-Medial: nasal septum

12. Nasal cartilages :
(a) Upper lateral cartilage (ULC)
-Attached superiorly to nasal bones
-Articulates inferiorly with the cephalic margin of the LLC most often forming an
interlocking scroll
-Thickens medially where it becomes continuous with the quadrangular cartilage
of the septum forming the cartilaginous portion of the nasal dorsum
(b) Lower lateral cartilage (LLC)
-Provides the shape of the nasal tip
-Composed of medial and lateral crura
(c) Sesamoid cartilages
-Small cartilages located lateral to the lateral crus

13. Nasal septum:
(a) Comprised of bony and cartilaginous components, lined by either
a mucoperiosteal or mucoperichondrial layer
-Cartilage = quadrangular cartilage
-Bone = perpendicular plate of ethmoid, vomer, crest of the maxillary bone,
crest of the palatine bone; minor contributions from crest of sphenoid bone
and nasal spine of frontal bone
(b) Membranous (mobile) septum:
Cartilage-deficient membrane adjoining the columella to the caudal septum
Site of hemitransfixion/transfixion incision

15. Surgical implications
*A deviated septum often involves the perpendicular
plate, the nasal crests of the maxilla and the palatine
bone, and, rarely, the vomer.
*A fracture of the anterior nasal spine may be
complicated by septal hematoma. A
hematoma should be drained bilaterally;
anteriorly in one nasal cavity and posteriorly
in the opposite side. A rubber drain should be
placed, as well as bilateral nasal packing to
reppose the perichondrium to the septum.
*A cartilaginous saddle nose, is due to depression of
the dorsum of the nose. It may be caused by the
following:
- Excessive removal of septal cartilage, which
weakens the normal support in this area.
- Traumatic fracture of the septum.
- Septal hematoma or abscess, because the blood
supply of septal cartilage is provided by the
covering perichondrium.
- Tuberculosis, syphilis, relapsing polychondritis,
Wegner’s granuloma.

16. Surgical implications
Surgical elevation of the nasal skin should be done in the
plane just superficial to the underlying bony and cartilaginous
nasal skeleton to prevent injury to the blood supply and to the
nasal muscles. Excessive damage to the nasal muscles
causes unwanted immobility of the nose during facial
expression, so called mummified nose

17. Nasal musculature:
(a) Elevators
Function = shortens nose and dilates nostrils
-Procerus
-Levator labii superioris alaeque nasi
-Anomalous nasi
(b) Depressors
Function = lengthens nose and dilates nostrils
-Depressor septi
-Alar nasalis
(c) Compressors
Function = lengthens nose and constricts nostrils
-Compressor narium minor
-Transverse nasalis

18. Anatomy of the nasal cavity
-Nasal valves
(a) Important contributors to nasal airway resistance
(b) Regions at greatest potential for collapse resulting in nasal airway
obstruction
Internal nasal valve:
-Bounded by nasal septum, caudal edge of ULC, anterior face of inferior turbinate
-Narrowest cross-sectional area of the nasal cavity and site of greatest nasal
airflow resistance
-Does not undergo change in dimension during inspiration

19. External nasal valve:
-Bounded by nasal ala laterally, nasal septum and columella medially
-Situated caudal to internal nasal valve
-Normally dilates during inspiration

20. Nasal vestibule:
(a) Entrance of nasal cavity lined by hair bearing skin, sebaceous and sweat
glands
(b) Boundaries:
-Medial = nasal septum
-Superior and lateral = LLC
-Inferior = alveolar process of maxilla
-Posterior = Limen nasi (Limen vestibule), formed by the caudal margin
of the ULC
(c) Posterior boundary coincides with the transition from the skin of the nasal
vestibule to the mucosal surface (pseudostratified ciliated columnar
epithelium) of the nasal cavity

21. Lateral nasal wall :
(a) Osteology of the lateral nasal wall (from anterior to posterior):
-Frontal process of maxilla
-Lacrimal bone
-Medial maxillary wall inferiorly, lamina papyracea (LP) superiorly
-Perpendicular plate of the palatine bone
-Medial pterygoid plate of the sphenoid bone Latter two
structures form the sphenopalatine foramen

22. (b) Lamella of the lateral nasal wall:
five lamella from anterior to posterior
-First lamella = uncinate process (UP)
-Second lamella = ethmoid bulla (EB)
-Third lamella = basal lamella of middle turbinate (MT)
-Fourth lamella = basal lamella of superior turbinate
-Fifth lamella = basal lamella of supreme turbinate (when present)

23. Meatus:
air space located beneath and lateral to the turbinate of the same name
-Inferior meatus: contains slit-like opening (termed Hasner valve)
corresponding to site of drainage of the nasolacrimal duct, located
approximately 1 cm posterior to anterior face of inferior turbinate
-Middle meatus: site of drainage of frontal, anterior ethmoid, and
maxillary sinuses
-Superior meatus: site of drainage of posterior ethmoid and sphenoid sinuses;
sphenoethmoidal recess located within posterior aspect of superior meatus

24. Turbinates
-Inferior, middle, superior, and occasionally supreme
-All originate from ethmoid bone except for inferior turbinate

25. Middle Turbinate (MT)
-Anterior end attaches to frontal process of maxilla forming axilla of the MT
-Has three sites of attachment oriented in three planes
Anterior portion of MT:
-Oriented in sagittal plane
-Attached to junction of cribriform plate and lateral lamella
-Delimits fovea ethmoidalis (roof of ethmoid sinus) from cribriform plate
Middle portion of MT (basal (ground) lamella):
-Oriented in coronal plane (vertical)
-Attached laterally to LP
-Delimits anterior and posterior ethmoid sinus

26. Posterior portion of MT ( horizontal attachment):
-Oriented in axial plane (horizontal)
-Attached to the crista ethmoidalis of the perpendicular process of palatine bone just
anterior to sphenopalatine foramen
-Potential site of postoperative epistaxis when MT is resected
-Preservation reduces risk of postoperative MT lateralization

27. Lacrimal (maxillary) line:
-Endoscopic landmark of suture line along medial orbital wall at the
junction of the frontal process of the maxilla and lacrimal bone
-Site of attachment of the UP to the lateral nasal wall
Uncinate process (UP):
-Crescent shaped, mucosal lined bone of ethmoid origin which shields natural
ostium of the maxillary sinus
-May narrow ethmoid infundibulum when pneumatized
-Vertical portion attaches anteriorly to the lacrimal line
-Horizontal portion attaches inferiorly to the inferior turbinate

28. -Site of superior attachment of vertical portion of UP determines frontal sinus drainage pathway
-Superior attachment to LP:-
- Frontal sinus drainage occurs medial to the UP, directly into the middle meatus
-Results in blind pouch of the superior portion of the ethmoid infundibulum
(termed Recessus Terminalis)
-Most common configuration (80%)
-Superior attachment to fovea ethmoidalis or MT:
-Frontal sinus drainage occurs lateral to the UP and directly into the ethmoid
infundibulum
-Less common configuration (20%)

30. Ethmoid infundibulum:
-Three-dimensional trough bounded by the UP medially, the LP laterally and the
EB posterosuperiorly
-Opens inferiorly at maxillary sinus ostium
Hiatus semilunaris:
-Two-dimensional, crescenteric window into the ethmoid infundibulum
-Bounded by UP anteriorly and EB posteriorly

32. Nasal fontanelles:
-Areas of bony dehiscence of the lateral nasal wall typically covered by mucosa of
the middle meatus, connective tissue and mucosa of the maxillary sinus
-Site of accessory ostia when mucosa absent, most commonly located in posterior
fontanelle (up to 30% of people)
Posterior fontanelle
-Located posterior to horizontal process of UP
-Located posterior to natural maxillary os and oriented in sagittal plane
(compared to oblique orientation of natural maxillary os)
Anterior fontanelle
- Located anterior to UP articulation with inferior turbinate

33. Osteomeatal complex (OMC):
Region within middle meatus ,its boundries:
Posterior: basal lamella of the MT
Medial: MT
Lateral: LP
Superior: fovea ethmoidalis
Region of interest in the pathophysiology of acute bacterial rhinosinusitis as it is a regional
confluence of drainage pathways of the maxillary, anterior ethmoid, and frontal sinuses.

35. Nasolacrimal system:
In the lateral nasal wall
Tear drainage pathway as follows:
Upper and lower lacrimal punctum → Upper and lower canaliculus → Common canaliculus
(present in 90%) →Valve of Rosenmüller (one-way valve preventing reflux into canaliculi)
→Lacrimal sac → Nasolacrimal duct → Valve of Hasner →Inferior meatus

36. Vascular anatomy:
Vascular anatomy of the external nose
(a) Facial artery branches (external carotid artery) →
- Angular artery → lateral nasal arterySupplies lateral surface of caudal nose
-Superior labial artery → columellar arterySupplies columella and nasal tip
(b) Ophthalmic artery branches (internal carotid artery)
- External nasal branch of anterior ethmoid artery Supplies nasal dorsum
and tip
-Dorsal nasal artery Supplies nasal dorsum

38. Vascular anatomy of the nasal cavity
(a) Internal carotid artery → ophthalmic artery → Anterior & posterior ethmoid
arteries
- Anrerior ethmoid artery (AEA):
Exits orbit between superior oblique & medial rectus muscle via anterior
ethmoid foramen (~24 mm posterior to anterior rim of lacrimal fossa) within
the frontoethmoid suture →Courses anteromedially along the skull base
either within a bony canal (dehiscent in 40%) or within a mesentery below
skull base →enters anterior cranial fossa medially by piercing the lateral
lamella, rendering it the weakest portion of the skull base (one-tenth as
strong as the fovea ethmoidalis)→Supplies anterior one-third of the nasal cavity

40. -Posterior ethmoid artery (PEA):
Exits orbit via posterior ethmoid foramen (12 mm posterior to anterior
ethmoid foramen, 6 mm anterior to optic ring) → Supplies posterior nasal cavity.
(b) External carotid artery branches: →
I- Internal maxillary artery (IMA) branches →
1-Descending palatine artery → greater palatine artery
Passes through greater palatine canal located along posterior aspect of the
perpendicular plate of the palatine bone Potential for injury with
dissection of the posterior medial maxillary wall at its junction with
posterior maxillary sinus wall
Supplies anteroinferior nasal cavity including nasal septum via incisive foramen.

41. 2-Pharyngeal branch of IMA :
Courses through pharyngeal canal which arises from the posterior wall of
the pterygopalatine fossa→ coursing posteriorly within the roof of the
nasopharynx → Supplies posterosuperior nasal cavity and nasopharynx
3 -Sphenopalatine artery (SPA) → Enters nasal cavity via sphenopalatine foramen
4 -Posterior septal branch → Courses along sphenoid rostrum inferior to natural
sphenoid os → Supplies nasal septum (vascular supply of pedicled
nasoseptal flap)
5 -Posterior lateral nasal branch → Runs along the middle and inferior turbinates,
providing their vascular supply

43. II- Facial artery branches
-Superior labial artery → alar branch
-Supplies nasal vestibule and anterior nasal cavity
Nasal cavity vascular plexuses
(a) Woodruff plexus:
- Aggregation of vessels (posterior lateral nasal + pharyngeal branch of IMA)
within the posterior inferior meatus
- Previously thought to be arterial, now shown to be venous in nature
(b) Kiesselbach plexus ( Little’s area)
- Located in the anterior nasal septum
- Most common site of anterior epistaxis
- Formed by posterior septal branch of SPA, AEA, greater palatine artery, alar
branch of superior labial artery

45. Venous drainageof external nose:
Venous drainage is into the facial vein, and then in turn into the internal jugular vein.

46. Venous drainage of nasal cavity:
(a) Anterior and posterior ethmoid veins → superior ophthalmic vein →
cavernous sinus
(b) Sphenopalatine vein → pterygoid plexusNNAs this is a valveless venous
system, there is a potential for retrograde spread of infection intracranially
(cavernous sinus in particular)
(c) Diploic veins of Breschet → Provide venous drainage of the frontal sinuses
→Course through multiple anterior and posterior table foramina (breschet’s
canals) → Communicate with the dural sinuses (cavernous sinus and
superior sagittal sinus) ,Contributes to intracranial spread of infection

48. Lymphatic drainage:
The anterior part of nasal cavity drains into submental and submandibular lymph nodes,
whereas, the posterior part into the retropharyngeal nodes. All of these nodes finally drain into
the upper deep cervical lymph nodes

49. Sensory innervation:
(a) External nose Branches of ophthalmic division of cranial nerveV(V1)
- Infratrochlear nerve supplies lateral nose above medial canthus
- External anterior ethmoidal nerve supplies nasal tip, dorsum and ala
(b) Branches of maxillary division of cranial nerve V (V2)
- Infraorbital nerve supplies lateral nose and ala
- Anterior superior alveolar nerve (branch of infraorbital nerve)minor
contribution to nasal tip and columella

51. (c) Nasal cavity
-Branches of ophthalmic division of cranial nerve V (V1)
- Internal nasal branch of anterior ethmoidal nerve supplies anterior and
superior regions of the nasal cavity
- Posterior ethmoidal nerve supplies posterior nasal cavity
- Branches of maxillary division of cranial nerve V (V2)
-Sphenopalatine (nasopalatine) nerve (anastomoses with greater palatine
nerve)supplies posterior nasal cavity
-Anterior superior alveolar nerve supplies anterior nasal cavity and nasal
floor

53. Autonomic innervation:
- Sympathetic innervation Function: vasoconstriction
Preganglionic: sympathetic chain
Ganglion: superior cervical ganglion
Postganglionic: deep petrosal nerve joins with greater superficial petrosal
nerve (GSPN) → vidian nerve (passes through sphenopalatine ganglion
without synapsing) → distributed to nasal mucosa with sensory nerves

55. -Parasympathetic innervation Function: vasodilation and mediates nasal secretions
Preganglionic: superior salivatory nucleus (CN VII) → nervus intermedius
(leaves CN VII at geniculate ganglion with GSPN to form vidian nerve)
Ganglion: sphenopalatine ganglion
Postganglioinic: distributed to nasal mucosa with deep branches of V2

56. Olfactory nerve
-Olfactory mucosa
-2 groups of unmyelinated fibres: lateral and medial fibers
-Cribiform plate of the ethmoid bone
-Olfactory bulb

57. THANKS