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The Nasal Septum - Detailed Notes

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1. Functions

• Divides the nasal airway into two distinct nasal cavities
• Supports the nasal dorsum and maintains its shape
• Maintains the shape of the columella and nasal tip
• Forms part of the internal and external nasal valves
• Contributes to laminar airflow, humidification, and filtering of inspired air
• Supports olfaction by directing airflow

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2. Structural Composition

2.1 Bony Portion

2.2 Cartilaginous Portion - The Quadrilateral (Septal) Cartilage

• Also called the quadrilateral cartilage
• Bound firmly by collagenous fibers to the nasal bones, perpendicular plate of ethmoid, and vomer
• Continuous with the upper lateral cartilages (ULCs) toward the bridge of the nose, forming a T-shaped structure at the dorsum
• A posterior projection called the sphenoidal process (or septal tail) extends posteriorly between the vomer and perpendicular plate of ethmoid; this can serve as a source of cartilage for revision rhinoplasty
• Inferior attachment: sits within the nasal crest of the maxilla, bound by looser connective tissue creating a pseudoarthrosis - this joint allows mobility during flexion, reducing fracture or dislocation risk with trauma

2.3 Membranous Septum

• A segment of connective tissue between the caudal portion of the septal cartilage and the columella
• Not cartilaginous or bony

2.4 Vomeronasal Cartilages (Jacobson's)

• Narrow strips of cartilage located between the inferior edge of the septal cartilage and the vomer
• Remnants of the vomeronasal organs from fetal development
• Often found in conjunction with a septal spur
• Can be used as cartilage grafting material when other sources are unavailable

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3. Nasal Septal Swell Body

• A widened region of the anterior nasal septum located anterior to the middle turbinate at the internal nasal valve
• Histology: increased venous sinusoids and fewer glandular elements compared to adjacent mucosa
• The high proportion of venous sinusoids suggests it can alter nasal airflow in a similar manner to the inferior turbinates

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4. Blood Supply

External Carotid Artery Branches (via maxillary artery)

Internal Carotid Artery Branches (via ophthalmic artery)

Kiesselbach's Plexus (Little's Area)

• Located on the anterior nasal septum
• Formed by anastomosis of the anterior ethmoid artery, posterior septal artery, and septal branch of the superior labial artery
• Rich vascular bed of long capillary loops
• Most common site of epistaxis (~90% of anterior nosebleeds) due to:
  • Rich vascular supply
  • Thin overlying mucosa
  • Susceptibility to injury from turbulent airflow and digital trauma

Venous Drainage

• Posteriorly: via sphenopalatine vessels into the pterygoid plexus
• Anteriorly: via facial veins
• Superiorly: ethmoidal veins communicate with the superior ophthalmic system; there may be direct intracranial connections through the foramen caecum into the superior sagittal sinus (clinically important for spread of nasal sepsis)

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5. Innervation

Sensory Innervation (Trigeminal Nerve)

• V1 (Ophthalmic): anterior and superior septum via branches of the nasociliary nerve (nasal branches)
• V2 (Maxillary): posterior septum via the nasopalatine nerve (CN V2), which runs through the incisive canal to the palate; provides sensation to the posteroinferior septum

Autonomic Innervation

• Parasympathetic: preganglionic fibers travel via CN VII → greater superficial petrosal nerve → joins deep petrosal nerve → vidian nerve → synapse in the sphenopalatine ganglion → postganglionic fibers innervate nasal mucosa (regulate secretions and vasodilation)
• Sympathetic: postsynaptic fibers pass through the sphenopalatine ganglion → nasal mucosa (regulate vasoconstriction, turbinate tone)
• The autonomic system regulates vascular tone, turbinate congestion, and nasal secretions

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6. Mucosa

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7. Embryology

• Nasal airway development begins at week 4 of gestation from neural crest cell proliferation forming nasal placodes
• The nasal septum develops as a downgrowth from the merged medial nasal processes and nasofrontal process
• Nasal septum and palatine processes begin fusing anteriorly at week 9; fusion is completed posteriorly by week 12
• The vomeronasal (Jacobson's) organs form as epithelial invaginations on either side of the septum; they begin to regress shortly before birth, leaving the vomeronasal cartilages as adult remnants
• Injury in young children can cause asymmetric growth of the entire nasal structure due to chondrocyte growth interruption

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8. Deviated Nasal Septum

• Extremely common - in adults the septum very frequently deviates from the midline, particularly at the junction of the cartilaginous and bony portions (where the vomeronasal cartilage lies)
• Most common cause of unilateral nasal airway obstruction

Causes

• Birth trauma (forceps delivery, passage through narrow pelvic canal)
• Nasal/midfacial trauma at any age
• Microfractures early in life heal with bending of cartilage away from the side of injury
• Developmental abnormalities

Clinical Features

• Nasal obstruction (unilateral or bilateral)
• Paradoxical nasal obstruction: some patients feel obstruction on the contralateral (more open) side, because the turbinate there may be hypertrophied as compensation
• Compensatory turbinate hypertrophy on the side contralateral to the deviation
• Impaired olfaction
• Chronic sinusitis
• Possible external nasal deformity
• Epistaxis (from secondary turbulent airflow causing mucosal drying and septal varices)

Nasal Cycle Interaction

• The nasal cycle is a normal alternating congestion of the two sides, cycling every 0.5-3 hours under sympathetic control
• In patients with a fixed septal deviation, the sensation of obstruction frequently mirrors the congestion phase of the cycle

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9. Clinical Relevance - Key Surgical Points

L-Strut Principle

Septal Perforation

• Recognized complication of septoplasty
• Prevention requires meticulous mucoperichondrial dissection; any bilateral membrane tears should be repaired with an interposition graft of crushed cartilage placed between flaps
• Causes include: iatrogenic, cocaine abuse, granulomatous disease (e.g., Wegener's/GPA, sarcoidosis), syphilis, trauma

Incisive Neurovascular Bundle

• A variably located incisive artery and its neural fibers are found at the inferior border of the vomer
• Relevant when trimming a badly deviated maxillary crest - injury may cause temporary numbness or pain of the central incisors or hard palate mucosa

Cottle Maneuver

• Gently pulling the cheek laterally to open the nasal valve; a positive test suggests nasal valve compromise, though it has many false positives
• More specific: gentle lateralization of the ULC with a cotton-tipped applicator or cerumen curette

Nasoseptal Flap

• Based on the posterior septal artery (branch of sphenopalatine artery)
• The workhorse pedicled flap for endoscopic anterior skull base reconstruction

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10. Summary Diagram of Arterial Supply

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Lateral Wall of the Nose - Detailed Notes

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1. Osteology (Bones Forming the Lateral Nasal Wall)

The sphenopalatine foramen is formed by the perpendicular plate of the palatine bone together with the sphenoid bone - it is the principal neurovascular gateway to the nasal cavity.

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2. The Five Lamellae of the Lateral Nasal Wall

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3. Turbinates (Conchae)

3.1 Overview

• Inferior, middle, superior, and occasionally supreme turbinate
• All turbinates originate from the ethmoid bone - except the inferior turbinate, which is an embryologically independent osseous structure (its own bone)
• Each turbinate creates a corresponding meatus (air space below and lateral to it)

3.2 Inferior Turbinate

• Largest turbinate; the most important for airflow resistance
• An independent bone (not part of the ethmoid)
• Lies along the inferior lateral wall; head is ~1 cm posterior to the nasal vestibule
• The nasolacrimal duct opens into the inferior meatus approximately 1 cm posterior to the anterior face of the inferior turbinate (at Hasner's valve)
• Contains a rich venous sinusoidal network (erectile tissue)
• Participates in the nasal cycle
• Compensatory hypertrophy occurs contralateral to a deviated nasal septum

3.3 Middle Turbinate (MT)

• Anterior end attaches to the frontal process of maxilla, forming the axilla of the MT
• The posterior horizontal attachment is a potential site of postoperative epistaxis if the MT is resected; its preservation reduces risk of postoperative MT lateralization

3.4 Superior (and Supreme) Turbinate

• Arises from the ethmoid bone
• The superior turbinate forms the lateral wall of the sphenoethmoidal recess (SER)
• A supreme turbinate may be present (5th lamella)

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4. Meatuses and Their Drainage

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5. Key Endoscopic Landmarks

5.1 Uncinate Process (UP)

• Crescent-shaped, mucosa-lined bone of ethmoid origin
• Shields the natural ostium of the maxillary sinus
• Vertical portion attaches anteriorly to the lacrimal (maxillary) line
• Horizontal portion attaches inferiorly to the inferior turbinate
• May narrow the ethmoid infundibulum if pneumatized

5.2 Ethmoid Infundibulum

• A three-dimensional trough/channel
• Bounded by: UP medially, lamina papyracea laterally, ethmoid bulla posterosuperiorly
• Opens inferiorly at the maxillary sinus ostium

5.3 Hiatus Semilunaris

• A two-dimensional crescentic window (slit) opening into the ethmoid infundibulum
• Bounded anteriorly by the UP and posteriorly by the ethmoid bulla

5.4 Ethmoid Bulla (EB)

• Second lamella; the largest and most consistent anterior ethmoid cell
• Forms the posterior boundary of the hiatus semilunaris

5.5 Lacrimal (Maxillary) Line

• Endoscopic landmark: the suture line along the medial orbital wall at the junction of the frontal process of maxilla and the lacrimal bone
• Site of attachment of the UP to the lateral nasal wall
• Divides the anterior lacrimal crest (maxilla) from the posterior lacrimal crest (lacrimal bone)

5.6 Nasal Fontanelles

• Areas of bony dehiscence of the lateral nasal wall covered only by mucosa and connective tissue (no bone)
• Posterior fontanelle: located posterior to the horizontal process of the UP, posterior to the natural maxillary ostium (oriented sagittally vs. the oblique natural ostium) - site of accessory ostia in up to 30% of people
• Anterior fontanelle: located anterior to the UP articulation with the inferior turbinate

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6. Osteomeatal Complex (OMC)

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7. Nasolacrimal System

• Anterior wall: anterior lacrimal crest (frontal process of maxilla)
• Posterior wall: posterior lacrimal crest (lacrimal bone)
• The suture between these corresponds to the lacrimal line

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8. Blood Supply of the Lateral Nasal Wall

External Carotid Artery (via Internal Maxillary Artery)

• Located within the superior meatus, between the basal lamella of the MT and superior turbinate
• Lies just inferior to the horizontal attachment of the middle turbinate
• The crista ethmoidalis (a crest on the perpendicular plate of the palatine bone) lies just anterior to the SPF - a consistent, reliable endoscopic landmark for identifying and ligating the SPA
• In one cadaver study, 97% of specimens had two or more branches of the SPA medial to the crista ethmoidalis - surgeons must control all branches for successful endoscopic ligation

Internal Carotid Artery (via Ophthalmic Artery)

• The AEA is difficult to access endoscopically - only ~20% lie in a mesentery that can be clipped transnasally
• Endoscopic removal of the lamina papyracea allows identification of both arteries between the periorbita and skull base
• Alternatively, an external approach via a modified Lynch incision is used

There is considerable overlap between internal and external carotid arterial systems on each side - this can complicate arterial ligation for epistaxis management.

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9. Innervation of the Lateral Nasal Wall

Sensory (Trigeminal Nerve)

The lateral wall of the nose and turbinates are specifically supplied by posterolateral nasal nerves from V2 arising from the sphenopalatine foramen and ethmoidal nerves from V1.

Autonomic Innervation

Key distinction: Parasympathetic fibers synapse in the sphenopalatine ganglion; sympathetic fibers pass through without synapsing.

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10. Mucosa and Epithelium

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11. Nasal Cycle

• A normal physiological alternating congestion of the two sides of the nasal cavity
• Cycle repeats every 0.5-3 hours under sympathetic nervous system control
• Total nasal resistance remains approximately constant as one side congests and the other decongests
• Turbinates are the primary structures involved (via their venous sinusoidal erectile tissue)
• Clinically relevant: in patients with a fixed septal deviation, nasal obstruction symptoms frequently fluctuate with the nasal cycle

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12. Clinical Summary Table

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Structures Opening into the Lateral Wall of the Nasal Cavity

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Overview Diagram

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Quick Reference Table

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1. Inferior Meatus

Nasolacrimal Duct (NLD)

• Opens into the anterior part of the inferior meatus
• Located approximately 1 cm posterior to the anterior face of the inferior turbinate
• The opening is guarded by the Valve of Hasner - a mucosal fold that acts as a one-way valve preventing air reflux into the lacrimal system (not a true valve anatomically)
• The full tear drainage pathway is: upper/lower punctum → canaliculus → common canaliculus → Valve of Rosenmuller → lacrimal sac → nasolacrimal duct → Valve of Hasner → inferior meatus
• Clinical note: Congenital obstruction of the NLD most commonly occurs at the Valve of Hasner; presents as epiphora and mucopurulent discharge in neonates. Nasolacrimal duct cysts (dacryocystoceles) may appear in the inferior meatus as a bluish cystic mass, causing nasal obstruction.

Nothing else drains into the inferior meatus - this is a frequently tested fact.

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2. Middle Meatus

2.1 Frontal Sinus

Frontal sinus
    ↓
Funnel-shaped infundibulum (within the frontal sinus)
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Frontal ostium (the waist of the hourglass)
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Frontal recess (the "1st tight spot" - narrowest part)
    ↓
Superior portion of middle meatus

• Anterior: agger nasi cell (most anterior ethmoid cell, present in most individuals)
• Posterior: ethmoid bulla
• Inferior: uncinate process (and its superior attachment determines whether drainage is medial or lateral to it)
• Medial: middle turbinate

2.2 Maxillary Sinus

Maxillary sinus
    ↓
Maxillary sinus ostium (natural ostium - located in superior medial wall of sinus)
    ↓
Ethmoidal infundibulum (3D trough; bounded by UP medially, lamina papyracea laterally, ethmoid bulla posterosuperiorly) - the "2nd tight spot"
    ↓
Hiatus semilunaris (2D crescentic window between UP anteriorly and ethmoid bulla posteriorly)
    ↓
Middle meatus

2.3 Anterior Ethmoid Cells

• The anterior ethmoid air cells drain into the middle meatus via their individual ostia, which open into the ethmoid infundibulum
• The ethmoid bulla (the largest and most consistent anterior ethmoid cell) drains superiorly into the suprabullar recess or directly into the middle meatus

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3. Superior Meatus

Posterior Ethmoid Cells

• All posterior ethmoid air cells drain into the superior meatus
• The superior turbinate forms the lateral wall of the sphenoethmoidal recess (SER)

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4. Sphenoethmoidal Recess (SER)

Sphenoid Sinus

• The sphenoid ostium opens into the sphenoethmoidal recess, behind (not medial or lateral to) the superior turbinate
• Located in the anterosuperior portion of the anterior sphenoid sinus wall, situated medially
• This constitutes the "3rd tight spot" of sinonasal drainage
• The sphenoethmoidal recess in turn leads to the posterior aspect of the superior meatus
• A supreme turbinate, when present, may also be visible here

• Approximately 30 mm from the anterior nasal spine
• Approximately 1.5 cm above the posterior choana
• Can also be found ~7 mm above the choanal arch, 1 cm from the nasal septum

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5. Summary by Sinus

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6. Clinical Correlates

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