The following CBME core competencies are covered in this chapter. EN1.1: Describe the anatomy of nose and paranasal sinus.

Anatomy of the Internal Nose (Nasal Cavity)

Introduction of Nasal Cavity

The nasal cavity extends from the external nares (nostrils) anteriorly to the posterior choanae, where it opens into the nasopharynx. The nasal septum divides it into right and left nasal cavities. Each nasal cavity has a roof, floor, medial wall (nasal septum), and lateral wall. The floor is concave from side to side, flat anteroposteriorly, and horizontally oriented.

Each nasal cavity measures approximately 5 cm in height and 5–7 cm in length. It is narrow transversely, measuring about 1.5 cm at the floor and only 1–2 mm at the roof.

The olfactory epithelium lines the roof of the nasal cavity, the superior turbinate, the upper part of the middle turbinate, and the superior part of the nasal septum. The remainder of the nasal cavity, except the nasal vestibule, is lined by respiratory epithelium, which continues with the respiratory mucosa of the upper and lower respiratory tract.

Functions of the Nasal Cavity

Functional Divisions. Based on function, the nasal cavity proper is divided into two regions:

1. Olfactory region: The olfactory region occupies the roof of the nasal cavity, the superior turbinate, and the superior one-third of the nasal septum. 
2. Respiratory part: The respiratory region forms the remainder of the nasal cavity proper. It is lined by ciliated pseudostratified columnar epithelium with goblet cells. 

Anatomical Divisions. Each nasal cavity can be divided into two main anatomical regions for clarity.

1. The Vestibule: The anterior and inferior portion, lined with skin containing vibrissae (coarse hairs).
2. The Nasal Cavity Proper: The nasal cavity proper lies posterior to the vestibule. It is lined by respiratory and olfactory mucosa and performs the major respiratory and olfactory functions of the nose.

Epithelial Lining of the Nasal Cavity

The nasal cavity contains three types of epithelium:

• Squamous epithelium: Lines the nasal vestibule.
• Olfactory epithelium: Lines the roof of the nasal cavity, superior turbinate, upper part of the middle turbinate, and superior part of the nasal septum.
• Respiratory epithelium: Ciliated pseudostratified columnar epithelium with goblet cells that lines the remainder of the nasal cavity.

Physiological Nasal Cycle

In healthy individuals, the two nasal cavities do not remain equally patent throughout the day. Instead, alternating congestion and decongestion of the erectile tissue of the inferior and middle turbinates occur under autonomic control, producing the physiological nasal cycle.

The cycle usually lasts between 2 and 6 hours, although considerable individual variation exists. Most individuals are unaware of this phenomenon because total nasal airflow remains adequate. The nasal cycle becomes clinically important when septal deviation or turbinate hypertrophy converts this normal physiological variation into symptomatic nasal obstruction.

Nerve Supply of the Nasal Mucosa

The nasal mucosa receives general sensory, autonomic, and special sensory (olfactory) innervation.

1. General Sensory Innervation. The trigeminal nerve (CN V) provides the general sensory supply through its ophthalmic (V1) and maxillary (V2) divisions.

Ophthalmic Division (V1)

• Anterior ethmoidal nerve: Supplies the anterosuperior part of the nasal septum and lateral wall.

Maxillary Division (V2)

• Nasopalatine nerve: Supplies the posterior and inferior part of the nasal septum.
• Posterior superior lateral nasal nerves: Supply the superior and middle turbinates and the posterior superior part of the lateral wall.
• Posterior inferior lateral nasal nerves (branches of the greater palatine nerve): Supply the inferior turbinate and the lower part of the lateral wall.

2. Autonomic Innervation

The autonomic nervous system regulates nasal blood flow, turbinate congestion, and glandular secretion.

• Parasympathetic Supply: Parasympathetic fibres arise from the facial nerve (CN VII) through the greater petrosal nerve. They join the deep petrosal nerve to form the nerve of the pterygoid canal (Vidian nerve) and synapse in the pterygopalatine ganglion. Postganglionic fibres stimulate secretion from the nasal glands.
• Sympathetic Supply: Sympathetic fibres arise from the superior cervical ganglion. They travel through the deep petrosal nerve and the nerve of the pterygoid canal, pass through the pterygopalatine ganglion without synapsing, and supply the blood vessels of the nasal mucosa. They produce vasoconstriction, reduce turbinate congestion, and decrease nasal secretions.

3. Special Sensory Innervation (Olfaction)

The olfactory nerves (cranial nerve I) provide special sensory innervation and are responsible for the sense of smell. It innervates the olfactory mucosa on the lateral nasal wall and nasal septum. These nerves originate from receptors present in the olfactory mucosa/ epithelium. The central filaments of the olfactory cells are arranged into 12–20 nerves which pass through the cribriform plate to the olfactory bulb in the brain. They can carry sheaths of dura, arachnoid and pia into the nasal cavity. Damage to these nerves may lead to conditions like cerebrospinal fluid (CSF) rhinorrhea or meningitis due to the disruption of the CSF barrier.

Diagram: Nerve Supply of the Nose

Nasal Cavity Proper

The nasal cavity proper consists of the medial wall (nasal septum), lateral wall, roof, and floor, each of which is described below.

Medial wall (Nasal septum)

The nasal septum is a central partition wall dividing the nasal cavity into two halves. Composed of bone and cartilage, it is lined on both sides by a mucous membrane and forms the medial wall of the nasal cavities. Although typically positioned in the midline, the nasal septum is often slightly deviated, which may impact airflow and breathing efficiency. It plays a critical role in maintaining the structural integrity of the nose and provides major structural support to the nasal dorsum and nasal tip. The septal cartilage is essential for maintaining the shape and function of the nose. Its damage or removal, such as in septal abscess, injuries, tuberculosis or excessive removal during septal surgery, leads to depression of the lower part of the nose and drooping of the nasal tip.

Parts of the nasal septum

1. Columellar septum. It is formed by columella which contains the medial crura of alar cartilages united together by fibrous tissue and covered on either side by skin.
2. Membranous septum. It is made of double skin layers with no bony or cartilaginous support. It is located between the columella and the caudal edge of the septal cartilage. Both the columellar septum and the membranous septum are freely movable from side to side.
3. Septum proper. It is formed by a rigid osteocartilaginous framework, covered with the membrane of the nasal mucosa. Its principal constituents are:

• The perpendicular plate of ethmoid bone,
• The vomer
• A large septal (quadrilateral) cartilage is wedged between the perpendicular plate of the ethmoid bone and the vomer bone anteriorly.
• Other bones that make minor contributions at the periphery are the crest of nasal bones, the nasal spine of the frontal bone, the rostrum of the sphenoid, the crest of palatine bones and the maxillary crest, and the anterior nasal spine of the maxilla.

The septal cartilage rests in a groove on the anterior edge of the vomer and rests anteriorly on the anterior nasal spine of the maxilla. Trauma or dislocation can lead to conditions like caudal septal deviation or septal spur respectively, both of which may obstruct the nasal airway. Additionally, the septum is fused to the upper lateral cartilages, so deviations often involve external nasal deformities.

Arterial supply of the Medial Wall of the Nasal Cavity (Nasal septum)

The nasal septum is supplied by both the internal and external carotid systems:

1. Internal carotid system. Anterior and posterior ethmoidal arteries (branches of the ophthalmic artery).
2. External carotid system. Sphenopalatine artery (nasopalatine and posterior medial nasal branches). Septal branch of the greater palatine artery. Septal branch of the superior labial artery.

Blood supply according to the location: 

• Anterosuperior part: supplied by anterior/posterior ethmoidal arteries.
• Anteroinferior part: supplied by the superior labial artery.
• Posterosuperior part: dominantly supplied by the sphenopalatine artery.
• Posteroinferior part: supplied by the greater palatine artery, which ascends through the incisive canal to supply the anterior nasal septum.

Key features and areas of nasal septum

1. Little’s area (Kiesselbach’s plexus). James Little in 1879 and the same plexus was described one year later by Kiesselbach. It is a vascular network in the anteroinferior nasal septum. It is formed by anastomoses of the anterior ethmoidal, sphenopalatine, greater palatine, and superior labial arteries. The common site for epistaxis (nosebleeds) and site for the origin of the bleeding polypus (haemangioma) of the nasal septum
2. Trauma and deviation. The septal cartilage is vulnerable to displacement from the vomerine groove or anterior nasal spine, leading to nasal obstruction.

Venous drainage of the nasal septum

Plexus forms in Little’s area, draining:

• Anteriorly into the facial vein.
• Posteriorly via the sphenopalatine vein to the pterygoid plexus.

Nerve supply of the nasal septum

General sensory nerves

• Anterosuperior: anterior ethmoidal nerve (V1).
• Anteroinferior: infraorbital nerve (V2) and greater palatine nerve (V2).
• Posterior 2/3rd: nasopalatine nerve (pterygopalatine ganglion).

Special sensory nerves

• The olfactory nerve (cranial nerve I) supplies the olfactory mucosa over the superior part of the nasal septum. (See Special Sensory Innervation under Nerve Supply of the Nasal Mucosa.)

Lateral wall: Turbinates and the Osteomeatal Unit (OMU)

The lateral wall is the most important surgical area of the internal nose because it houses the drainage pathways for most paranasal sinuses. This wall is formed by eight separate bones, creating projections (Turbinates/Conchae), and channels (Meatuses) that contribute to airflow regulation, humidification, and drainage of the sinuses.

Bones of the lateral nasal wall

The lateral nasal wall is formed by eight separate bones, each of which has processes that articulate intricately with each other.

• Large bones: Maxilla (paired bone), Ethmoid, Frontal, Sphenoid bone (unpaired bones lying in the midline)
• Small bones: Palatine, Lacrimal, Inferior turbinate, Nasal bones (all are paired bones)
• Despite the presence of two sphenoid, two frontal, and two ethmoid sinuses, there is only one sphenoid bone, one frontal bone, and one ethmoid bone in the midline of the skull. This arrangement highlights the shared role of these unpaired bones in creating bilateral structures within the nasal cavity.

Turbinates/Conchae and Meatuses

• Turbinates or Conchae. There are three and occasionally four scroll-like bony projections present on the lateral wall of the nose called as turbinates or conchae. They are covered by the mucus membrane. The function of the conchae is to expand the surface area of the nasal cavity, allowing more inspired air to come into contact with the cavity walls. They also regulate the airflow so that the air remains in the nasal cavity longer, allowing sufficient time for humidification and temperature regulation. The turbinates create four channels. Three of these channels are termed meatuses, and the fourth is the sphenoethmoidal recess
• Meatuses. The spaces below the turbinates are called meatuses, creating pathways for the air to flow. These pathways are vital for directing air to different regions of the cavity and into the respiratory tract. The sphenoethmoidal recess is located above and medial to the superior turbinate, which is the drainage site of the sphenoid sinus.

Inferior turbinate. It is a distinct, scroll-like bone located on the lateral wall of the nasal cavity. It is larger and more straight in course compared to the middle and superior turbinates. The superior border is firmly attached to the maxilla (anteriorly) and the palatine bone (posteriorly), while the lower edge is free and hangs over the inferior meatus, creating a passage for airflow and drainage. The eustachian tube lies approximately 1 cm behind the posterior attachment of the inferior turbinate.

The inferior turbinate contains abundant venous sinusoids within its submucosa, forming erectile tissue that undergoes cyclical congestion and decongestion under autonomic control. This vascular tissue helps regulate nasal resistance, humidify inspired air and warm inhaled air. Excessive congestion occurs in allergic and vasomotor rhinitis and contributes significantly to nasal obstruction.

Inferior meatus. It is a space below the inferior turbinate. The nasolacrimal duct drains into the inferior meatus. It is approximately 1 cm behind the anterior end of the inferior turbinate, and it is guarded by a mucosal valve called Hasner’s valve.

Middle turbinate. The middle turbinate is part of the ethmoid bone. It has an S-shaped, dried leaf-like, curved structure. The posterior end of the middle turbinate ends at the level of the roof of the posterior choana. The middle turbinate is divided into three parts based on its orientation and attachments:

• Anterior Third part: Lies in the sagittal plane and is attached to the cribriform plate.
• Middle Third part: Lies in the coronal plane and is attached to the lamina papyracea, forming the ground lamella or basal lamella. The basal lamella divides the ethmoid cells into two groups: The anterior ethmoid cells, which lie anterior to the ground lamella of the middle turbinate and drain in the middle meatus. The posterior ethmoid cells, which lie behind (posterior) the ground lamella and drain into the superior meatus or sphenoethmoidal recess. The ground lamella of the middle turbinate is an important surgical landmark because it separates the anterior and posterior ethmoid air cells. During functional endoscopic sinus surgery, crossing the ground lamella signifies entry into the posterior ethmoid compartment. Identification of this landmark helps maintain surgical orientation and reduces the risk of injury to the orbit and skull base.
• Posterior Third part: Lies in the horizontal plane and extends posteriorly towards the choana. It is attached to the lateral nasal wall through the basal (ground) lamella and adjacent ethmoidal structures. It contributes to the roof of the posterior part of the middle meatus. The lamina papyracea and, consequently, the orbit are located approximately 2–3 mm lateral to the natural maxillary ostium, an important relationship during endoscopic sinus surgery.

Concha bullosa. Pneumatization of the middle turbinate leads to an enlarged, balloon-out middle turbinate called concha bullosa. Its drainage is variable and most commonly occurs into the middle meatus, depending on the pattern and extent of pneumatization.

Middle meatus. The middle meatus is an important area in the nasal cavity that plays an important role in frontal, maxillary and anterior ethmoidal sinuses drainage. Most anteriorly in the middle meatus, there is a curved bony structure called the uncinate process. Just behind the uncinate lies the ethmoidal bulla, a well-pneumatized and consistent anterior ethmoidal cell. Between the uncinate process and the ethmoidal bulla is a semilunar gap called the hiatus semilunaris, which is a flat, two-dimensional space. This gap leads to a three-dimensional area known as the infundibulum. Together, the uncinate process, the ethmoidal bulla, hiatus semilunaris and the infundibulum form the osteomeatal complex. 

Functional Importance of the Osteomeatal Complex: The osteomeatal unit acts as the common functional pathway for ventilation, drainage and mucociliary clearance of the frontal, maxillary and anterior ethmoidal sinuses. Even minor mucosal oedema within this narrow region may obstruct sinus drainage despite normally patent sinus ostia. Obstruction of the OMC impairs sinus ventilation and mucociliary clearance, predisposing to chronic rhinosinusitis. Restoration of OMC drainage is the principal objective of functional endoscopic sinus surgery (FESS).

Diagram: Schematic representation of the osteomeatal complex in coronal sections

 

Important structures in the middle meatus.

• Uncinate Process. The uncinate process is a sickle-shaped, hook-like bony structure located on the lateral wall of the nasal cavity. Positioned almost freely within the middle meatus, it partially covers the opening of the maxillary sinus. Anteriorly, the uncinate process articulates with the lacrimal bone, while posteriorly, it connects to the inferior turbinate and the perpendicular plate of the palatine bone. Its orientation extends from an anterosuperior to a posteroinferior direction. The anteroinferior border of the uncinate process attaches to the lateral nasal wall, whereas the posteroinferior end attaches to the inferior turbinate. This attachment divides the membranous portion of the lower middle meatus into two regions: the anterior and posterior fontanelle.
  
  Variations in Superior Attachment of the Uncinate Process: The superior end of the uncinate process shows anatomical variation. It may attach to the lamina papyracea, skull base (fovea ethmoidalis), or middle turbinate. These variations determine the drainage pathway of the frontal sinus. When attached to the lamina papyracea, the frontal sinus usually drains medial to the uncinate process directly into the middle meatus. When attached to the skull base or middle turbinate, drainage usually occurs through the ethmoidal infundibulum. Recognition of these variations is important during functional endoscopic sinus surgery to avoid incomplete frontal recess clearance.
  
  

  

  Diagram: Variations in the Superior Attachment of the Uncinate Process and Their Effect on Frontal Sinus Drainage
  (1) Attached to the cribriform plate (2) Attached to the middle turbinate (3) Attached to the lamina papyracea
  
  

• Hiatus Semilunaris. The posterosuperior border of the uncinate process is sharp and runs parallel to the anterior border of the ethmoidal bulla. This configuration creates a narrow gap between these two structures, referred to as the hiatus semilunaris (inferior). The hiatus semilunaris is a two-dimensional space approximately 1–2 mm in width.
• Infundibulum. The infundibulum is a three-dimensional space. Its principal medial boundary is formed by the uncinate process. Anteriorly, it is related to the frontal process of the maxilla and, occasionally, the lacrimal bone, while laterally it is bounded by the lamina papyracea. The natural opening (ostium) of the maxillary sinus is located in the lower portion of the infundibulum.  Additionally, accessory ostia of the maxillary sinus may occasionally be observed in the anterior or posterior fontanelle. When both the natural and accessory maxillary ostia are present, mucus may circulate repeatedly between the two openings instead of draining normally into the middle meatus. This “mucus recirculation phenomenon” may contribute to persistent symptoms following sinus surgery if the accessory ostium is not recognised. During endoscopic sinus surgery, accessory maxillary ostia should not be mistaken for the natural ostium. Failure to identify and connect the natural ostium with an accessory ostium may result in persistent mucus recirculation and continued symptoms despite technically successful surgery.
• Nasal Fontanelles. The anterior and posterior nasal fontanelles are membranous areas of the lateral nasal wall where bone is absent. They lie adjacent to the uncinate process and are clinically important because accessory maxillary ostia commonly develop in these regions, particularly in patients with chronic rhinosinusitis.
• Bulla ethmoidalis (anterior ethmoidal cell). The bulla ethmoidalis is a constant anterior ethmoidal air cell located posterior to the uncinate process. Its anterior surface forms the posterior boundary of the hiatus semilunaris. The degree of pneumatization varies considerably, ranging from minimal to extensive. The bulla may extend superiorly to the skull base and posteriorly to fuse with the ground lamella. In some cases, the bulla does not reach the skull base or the ground lamella, resulting in the formation of the suprabullar recess (above the bulla) and retrobullar recess (behind the bulla).
• Lateral sinus (sinus lateralis of Grunwald). The suprabullar recess and the retrobullar recess together create a semilunar space known as the lateral sinus. The lateral sinus opens into the middle meatus via a semilunar cleft, the hiatus semilunaris superioris, which is oriented opposite to the hiatus semilunaris inferioris. Therefore, the hiatus semilunaris inferioris leads into the infundibulum, while the hiatus semilunaris superioris opens into the lateral sinus. Posteriorly, the lateral sinus may extend to the basal lamella of the middle turbinate.
  Boundaries of the lateral sinus: Superiorly: Skull base. Laterally: Lamina papyracea. Medially: Middle turbinate. Inferiorly: Ethmoidal bulla
• Frontal recess. The frontal recess is an opening at the lower part of the frontal sinus that facilitates its drainage. The frontal sinus outflow tract varies based on the attachment of the uncinate process. In most cases, the uncinate process attaches to the lamina papyracea, allowing direct drainage into the middle meatus. Alternatively, when the uncinate attaches to the ethmoid roof or middle turbinate, the sinus drains into the ethmoid infundibulum. The frontal infundibulum, frontal ostium, and frontal recess form an “hour-glass configuration,” with the frontal sinus positioned more anteriorly than the frontal recess in endoscopic views. The upper end of the uncinate process resides within the frontal recess.
  The frontal recess is the most anatomically variable region of the sinonasal cavity. Numerous anatomical variations, including agger nasi cells, frontal cells, suprabullar cells and intersinus septal cells, may influence frontal sinus drainage. Understanding these variations is essential before endoscopic frontal sinus surgery and forms an important part of pre-operative CT evaluation.
  Boundaries of the Frontal Recess:
  • Anteriorly: Anterior wall of the agger nasi cell.
  • Posteriorly: Bulla ethmoidalis (or the suprabullar recess if present).
  • Laterally: Lamina papyracea, which appears yellowish due to the underlying orbital fat.
  • Medially: Middle turbinate.
  • Superiorly: The frontal recess opens via the frontal ostium into the frontal sinus.
• Agger nasi. It is a distinct bulge just anterior to the attachment of the middle turbinate. Pneumatization of the frontonasal process, along with the adjacent lacrimal bone, contributes to the formation of the agger nasi cells. They are usually 1-3 in number. Their size depends on the extent of pneumatization of the lacrimal bone and the adjacent frontonasal process of the maxilla. When pneumatized, it contains air cells, the agger nasi cells, which communicate with the frontal recess. An enlarged agger nasi cell may encroach on the frontal recess area, constricting it and causing mechanical obstruction to frontal sinus drainage.
• Haller cells are air cells located in the roof of the maxillary sinus (or floor of the orbit), derived from the pneumatization of anterior or posterior ethmoid cells. Enlargement of Haller cells can intrude on the ethmoid infundibulum, disrupting normal drainage of the maxillary sinus via its natural ostium.

Endoscopic approaches to the frontal recess and associated structures require careful navigation through four main anatomical barriers in the coronal plane:

1. 1. The uncinate process.
   2. The anterior wall of the bulla ethmoidalis.
   3. The ground lamella.
   4. The anterior wall of the sphenoid sinus.

Understanding the spatial relationships and variations of these structures is critical for effective endoscopic sinus surgery. High-resolution CT of the paranasal sinuses is the investigation of choice for evaluating osteomeatal anatomy before functional endoscopic sinus surgery. CT identifies anatomical variations such as concha bullosa, Haller cells, Onodi cells, agger nasi cells and variations in the uncinate process, enabling safer surgery and reducing complications involving the orbit and skull base.

Superior turbinate. The superior turbinate is part of the ethmoid bone. It is located posterior and superior to the middle turbinate. It may become pneumatized by one or more cells. It serves as a key landmark for identifying the ostium of the sphenoid sinus (sphenoethmoidal recess). The sphenoethmoidal recess gets its name from the fact that this area forms a niche between the posterior ethmoid cells and the sphenoid sinus. The sphenoid sinus ostium is positioned 2–3 mm above and medial to the superior turbinate and can be accessed endoscopically approximately 1–1.5 cm above the roof of the posterior choana, near the posterior borde the nasal septum. The superior turbinate is considered one of the most reliable landmarks during endoscopic sphenoidotomy because the sphenoid sinus ostium usually lies medial to its posterior attachment.

Superior meatus. It is a space below the superior turbinate. Posterior ethmoid cells open into it. The number of posterior ethmoid cells varies from 1 to 5. In 10 percent of cases, a posterior ethmoidal cell may extend posteriorly above or by the side of the sphenoid sinus. It may extend for as much distance as 1.5 cm from the anterior surface of the sphenoid. This extension of the cell is called as the Onodi cell (extension of the posterior ethmoidal cell). The Onodi cell is surgically important as the Onodi cell, when present, insinuates itself between the optic nerve and the sphenoid sinus. The optic nerve, therefore, produces a bulge in the lateral wall of the Onodi cell instead of in the sphenoid sinus. Normally, the lateral wall of the sphenoid sinus features two distinct bulges: the optic nerve superiorly and the internal carotid artery inferiorly and posteriorly.

Supreme turbinate. It is sometimes present above the superior turbinate and has a narrow meatus beneath it.

Arterial Supply of the Lateral Wall of the Nasal Cavity

The nose is richly supplied by both the external and internal carotid systems on the lateral walls and septum.

Internal carotid system

1. Anterior ethmoidal artery – Originates from the ophthalmic artery in the orbit. Both anterior and posterior ethmoidal artery supply the anterosuperior quadrant. During sinus surgeries, transection of this artery can result in retraction of the bleeding end into the orbit causing serious complications, such as pressure haematoma and potential loss of vision.
2. Posterior ethmoidal artery – Originates from the ophthalmic artery in the orbit. It is smaller than the anterior ethmoidal artery and is present in only 80% of individuals.

External carotid system

1. Branches of sphenopalatine artery – It is a terminal branch of the maxillary artery. It enters the nasal cavity via the sphenopalatine foramen. Posterior lateral nasal branch supplies a large part of the lateral wall (inferior and middle turbinate and meatii) and septum. Posterior septal branch supplies the posterior part of the septum.
2. Greater palatine artery – Originates from the maxillary artery in the pterygopalatine fossa. Supplies the anterior nasal cavity floor and medial wall-anastomoses with sphenopalatine and superior labial arteries.
3. Nasal branch of anterior superior dental – Originates from the infraorbital branch of maxillary artery
4. Branches of the facial artery to nasal vestibule.

• Anterosuperior part: supplied by anterior/posterior ethmoidal arteries.
• Anteroinferior part: supplied by the branches from the facial artery.
• Posterosuperior part: dominantly supplied by the sphenopalatine artery.
• Posteroinferior part: supplied by the greater palatine artery.

Venous drainage of the Lateral Wall of the Nasal Cavity

The veins follow the arteries within the mucosa. The veins form a plexus that drains anteriorly into the facial vein; the middle part to the pterygoid plexus of veins and posteriorly, into the pharyngeal plexus of veins.

Key features and areas of the Lateral Wall of the Nasal Cavity

1. Retrocolumellar Vein.The retrocolumellar vein runs vertically 2mm behind the columella (the tissue separating the nostrils). It crosses the floor of the nose and drains into the venous plexus located on the lateral nasal wall. This vein is a common site of venous bleeding, particularly in young individuals.
2. Woodruff’s Plexus. Woodruff’s plexus is a network of veins located below the posterior end of the inferior turbinate. It is a significant site for posterior epistaxis (nosebleeds), which is more commonly seen in adults.

Nerve Supply of the Lateral Wall of the Nasal Cavity

1. General Sensory Nerves. General sensory nerves, branches of the trigeminal nerve, innervate the entire lateral wall of the nasal cavity. The distribution is divided into four quadrants:

• Anterosuperior Quadrant – Supplied by the anterior ethmoidal nerve, a branch of the ophthalmic nerve (V1).
• Anteroinferior Quadrant – Supplied by the infraorbital nerve, which is a continuation of the maxillary nerve (V2).
• Posterosuperior Quadrant – Supplied by the lateral posterior superior nasal branches from the pterygopalatine ganglion (V2).
• Posteroinferior Quadrant – Supplied by the anterior palatine nerve, another branch from the pterygopalatine ganglion (V2).

2. Special Sensory Nerves (Olfactory Nerves). The olfactory nerve (cranial nerve I) supplies the olfactory mucosa over the superior part of the nasal septum. (See Special Sensory Innervation under Nerve Supply of the Nasal Mucosa.)

Autonomic Innervation. The autonomic supply of the lateral nasal wall is identical to that of the nasal mucosa. (See Autonomic Innervation under Nerve Supply of the Nasal Mucosa.)

 

Roof of the Nasal Cavity

The roof of the nasal cavity is divided into three parts:

• Anterior sloping part: Formed by the nasal bones and nasal part of the frontal bone.
• Posterior sloping part: Composed of the inferior surface of the body of the sphenoid bone.
• Middle horizontal part: Made by the cribriform plate of the ethmoid bone, allowing olfactory nerve fibres to pass.

Floor of the Nasal Cavity

The floor consists of two main structures:

• Anterior three-fourths: Palatine process of the maxilla.
• Posterior one-fourth: Horizontal plate of the palatine bone.

——– End of the chapter ——–

High-Yield Points for Quick Revision

• The Nasal Valve is the narrowest part of the airway and the primary site of nasal resistance.
• The Osteomeatal Unit (OMU) is the functional drainage pathway for the frontal, maxillary, and anterior ethmoid sinuses.
• Little’s Area on the anteroinferior septum is the most common site for anterior epistaxis.
• Woodruff’s Plexus behind the inferior turbinate is a common site for posterior epistaxis.
• The Middle Turbinate is the most important landmark for endoscopic sinus surgery.
• The Uncinate Process is the key to locating the maxillary sinus natural ostium and understanding frontal sinus drainage.
• The Lamina Papyracea is the paper-thin medial orbital wall, a common site for iatrogenic orbital entry during surgery.
• The Anterior Ethmoidal Artery is at risk during surgery; if severed, it can retract into the orbit, causing a sight-threatening hematoma.
• The Cribriform Plate is the thinnest part of the anterior skull base; injury causes CSF rhinorrhea and risk of meningitis.
• An Onodi Cellcan harbour the optic nerve, making it vulnerable during posterior ethmoidectomy.
• The Nasolacrimal Duct drains into the inferior meatus, about 1 cm behind the anterior end of the inferior turbinate.

Mnemonic for Bones of Lateral Wall: My Eye Please Look In Some New Places (Maxilla, Ethmoid, Palatine, Lacrimal, Inferior Turbinate, Sphenoid, Nasal).

Mnemonic for Little’s Area Arteries: Please Send Great Softness And Love (sPhenopalatine, Superior labial, Greater palatine, Anterior ethmoidal).

NEET PG & University Exam Style MCQs

1. A 45-year-old male presents with recurrent episodes of severe posterior epistaxis requiring posterior nasal packing. Which of the following is the most likely source of bleeding? A. Kiesselbach’s plexus B. Sphenopalatine artery C. Anterior ethmoidal artery D. Superior labial artery
2. During Functional Endoscopic Sinus Surgery (FESS) for chronic sinusitis, the surgeon must identify the middle turbinate as a key landmark. Which of the following structures forms the posterior attachment of the middle turbinate? A. Cribriform plate B. Lamina papyracea C. Uncinate process D. Basal lamella (Ground Lamella)
3. A patient develops clear, watery rhinorrhea after a head injury. A beta-2 transferrin test is positive. Which anatomical structure is most likely injured? A. Lamina papyracea B. Cribriform plate of ethmoid C. Vomer bone D. Perpendicular plate of ethmoid
4. The natural ostium of the maxillary sinus opens into which of the following anatomical spaces? A. Superior meatus B. Hiatus semilunaris C. Inferior meatus D. Infundibulum
5. What is the most common site of nasal obstruction due to its role as the major flow-limiting segment? A. Choana B. Nasal vestibule C. Internal nasal valve D. Sphenoethmoidal recess
6. An enlarged air cell located in the roof of the maxillary sinus, which can compromise the maxillary sinus ostium, is known as: A. Agger nasi cell B. Onodi cell C. Haller cell D. Concha bullosa
7. Which artery is a branch of the ophthalmic artery and is at risk of retracting into the orbit if transected during sinus surgery, potentially causing an orbital hematoma? A. Sphenopalatine artery B. Posterior ethmoidal artery C. Greater palatine artery D. Anterior ethmoidal artery
8. The nasolacrimal duct drains into which part of the nasal cavity? A. Superior meatus B. Middle meatus C. Sphenoethmoidal recess D. Inferior meatus
9. A pneumatized posterior ethmoid air cell that extends superiorly and laterally to the sphenoid sinus, creating a close relationship with the optic nerve, is called: A. Agger nasi cell B. Onodi cell C. Haller cell D. Concha bullosa
10. The sensory nerve supply to the anteroinferior part of the nasal septum is provided by: A. Anterior ethmoidal nerve B. Nasopalatine nerve C. Infraorbital nerve D. Greater palatine nerve

Frequently Asked Questions in Viva

• What is the most common site for nosebleeds?
  The most common site for epistaxis is Little’s area (Kiesselbach’s plexus) on the anteroinferior part of the nasal septum.
• Why is the lateral wall of the nose more important than the medial wall for surgeons?
  The lateral wall houses the drainage pathways (osteomeatal unit) for all the major paranasal sinuses, making it the primary focus of endoscopic sinus surgery.
• What is the function of the turbinates?
  Turbinates increase the surface area of the nose to warm, humidify, and filter inspired air, and they help regulate airflow by creating turbulence.
• How can a nasal septal abscess lead to a saddle nose deformity?
  A septal abscess can destroy the nutrient supply to the septal cartilage, leading to its necrosis and resorption. Since this cartilage supports the nasal dorsum, its loss causes the bridge to collapse.
• What is the danger area of the face?
  The danger area comprises the upper lip, nose, and adjacent areas, as infections here can spread via venous connections to the cavernous sinus in the skull.
• Which nerve is responsible for the sense of smell?
  The Olfactory Nerve (Cranial Nerve I) is responsible for the special sense of smell.
• What is the key landmark for locating the sphenoid sinus ostium during endoscopy?
  The superior turbinate is the key landmark. The sphenoid sinus ostium is located in the sphenoethmoidal recess, medial and superior to the superior turbinate’s posterior attachment.

——– End ——–

Reference Textbooks.

• Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
• Cummings, Otolaryngology-Head and Neck Surgery.
• Stell and Maran’s, Textbook of Head and Neck Surgery and Oncology.
• Ballenger’s, Otorhinolaryngology Head And Neck Surgery
• Susan Standring, Gray’s Anatomy.
• Frank H. Netter, Atlas of Human Anatomy.
• B.D. Chaurasiya, Human Anatomy.
• P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
• Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
• Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery.
• Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
• Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
• Arnold, U. Ganzer, Textbook of  Otorhinolaryngology, Head and Neck Surgery.
• Ganong’s Review of Medical Physiology.
• Guyton & Hall Textbook of Medical Physiology.

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