Anatomy of Internal Nose

ANATOMY OF INTERNAL NOSE

The internal nose plays a crucial role in breathing, filtering, and conditioning air. The internal nose comprises two nasal cavities, separated by the nasal septum. Each nasal cavity is approximately 5 cm in height and 5–7 cm in length. It is narrow transversely, measuring approximately 1.5 cm at the floor and only 1–2 mm at the roof. Each nasal cavity communicates with the external environment via the naris (nostril) and connects to the nasopharynx through the posterior nasal aperture or the choana (posterior nasal aperture). Structurally, each nasal cavity consists of a

1. The Vestibule: A skin-lined portion.
2. The Nasal Cavity Proper: A mucosa-lined portion.

VESTIBULE OF NOSE

The vestibule forms the anterior and inferior part of the nasal cavity. It is lined with skin containing sebaceous glands, hair follicles, and small hairs called vibrissae. The upper limit of the vestibule is marked by the limen nasi, also referred to as the nasal valve.

Clinical significance:

1. Acute infection of the hair follicle by Staphylococcus aureus causes exquisitely painful furuncle or boil.

2. Behind the vestibule is the atrium, a smooth region lined by nasal mucosa. The atrium when pneumatized exhibits a bulge caused by the agger nasi cell, which lies anterior to the middle turbinate. The agger nasi cells are the most anterior ethmoid air cells. They communicate with the frontal recess and play a critical role in frontal sinus drainage. When an agger nasi cell becomes enlarged or excessively pneumatized, it may encroach upon the frontal recess, narrowing or constricting this area. This mechanical obstruction can impede the drainage pathway of the frontal sinus, potentially leading to conditions such as frontal sinusitis due to poor ventilation and mucus retention.

Key Features of the Vestibule:

1. The Nasal Valve. The nasal valve is a critical structure in the nasal cavity, serving as a regulator of airflow. The angle between the nasal septum and the lower border of the upper lateral cartilage is approximately 30°.
Boundaries of the Nasal Valve.

1. • Laterally: Lower border of the upper lateral cartilage, fibrofatty tissue and anterior end of the inferior turbinate
   • Medially: The cartilaginous nasal septum.
   • Inferiorly: The floor of the pyriform aperture.

2. Nasal Valve Area. This area represents the narrowest cross-sectional region of the nasal cavity. It plays a vital role in regulating airflow during inhalation and controlling nasal resistance.

NASAL CAVITY PROPER

It can be further divided into two functional parts:

• Respiratory part – It is lined by a ciliated pseudostratified epithelium, which includes mucus-secreting goblet cells. It is primarily responsible for air conditioning by filtration, warmification, and humidification of the inhaled air.
• Olfactory region – It is lined by olfactory cells containing specialized olfactory receptors for the sense of smell. It is located at the apex of the nasal cavity.

The structure of each nasal cavity proper includes:

• Lateral wall
• Medial wall
• Roof
• Floor

LATERAL WALL

It is formed by several bones, projections, and 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.

Bony projections and meatuses:

1. 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 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
2. 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 straighter 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.

Inferior meatus. It is a space below the inferior turbinate. The nasolacrimal duct drains in 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 drains into the superior meatus or sphenoethmoidal recess.
• Posterior Third part: Lies in the horizontal plane and is attached to the lamina papyracea, medial wall of maxillary sinus and the perpendicular plate. It forms the roof of the middle meatus. The lamina papyracea and consequently the orbit is located 2-3 mm above the level of the maxillary ostium.

Concha bullosa. Pneumatization of middle turbinate leads to an enlarged ballooned out middle turbinate called concha bullosa. It drains into frontal recess directly or through agger nasi cells.

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 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 into a three-dimensional area known as the infundibulum. Together, the uncinate process, the ethmoidal bulla, and the infundibulum form the osteomeatal unit.

Important structures in 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.
• 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 bordered medially by the uncinate process, the frontal process of the maxilla, and sometimes the lacrimal bone. 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.
• Bulla Ethmoidalis (Anterior ethmoidal cell). The bulla ethmoidalis is a prominent ethmoidal air cell located posterior to the uncinate process. Its anterior surface forms the posterior boundary of the hiatus semilunaris. The degree of pneumatization of the bulla varies; it may present as a pneumatized cell or as a solid bony prominence. 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 recesses: the suprabullar recess (above the bulla) and the 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 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.
  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 an distinct bulge just anterior to the attachment of 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 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.

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). 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 border of the nasal septum. 

Superior meatus. It is a space below the superior turbinate. Posterior ethmoid cells open into it. Number of posterior ethmoid cells varies from 1 to 5. In 10 percent 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 sphenoid. This extension or the cell is called as the Onodi cell (extension of the posterior ethmoidal cell). 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

Internal carotid system

1. Anterior ethmoidal artery – Originates from the ophthalmic artery in the orbit. Supplies the nasal cavity, medial and lateral walls, and external nose through the external nasal branch. During sinus surgeries, injury to this artery can cause serious complications, such as CSF leak, retrobulbar hematoma, optic nerve compression, and potential loss of vision.
2. Posterior ethmoidal artery – Originates from the ophthalmic artery in the orbit Supplies the upper and posterior nasal septum.

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 of sphenopalatine artery supplies a large part of the lateral wall (turbinates and meatii) and septum—anastomoses with branches from ethmoidal arteries, facial artery, and greater palatine artery.
  • Posterior septal branch of the sphenopalatine artery supplies the medial wall 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.

 

• The anterior ethmoidal artery and the posterior ethmoidal artery supply the anterosuperior quadrant.
• Branches from the facial artery supply the anteroinferior quadrant.
• A few branches of the sphenopalatine artery supply the posterosuperior quadrant.
• The posteroinferior quadrant is supplied by branches from the greater palatine artery which pierce the perpendicular plate of palatine bone and passes up through the incisive fossa.

Venous drainage of the Lateral Wall of the Nasal Cavity

1. Retrocolumellar Vein. The retrocolumellar vein runs vertically 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 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.

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, supporting the nasal tip and bridge (dorsum of the cartilaginous part of the nose). 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:

1. • 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 crest maxilla, 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 vomer. 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.

 Blood supply of nasal septum

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

• Internal carotid system
  • Anterior and posterior ethmoidal arteries (branches of the ophthalmic artery).
• 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.

• 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.

Key features and areas of nasal septum

1. Little’s area (Kiesselbach’s plexus)
   • 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 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 nasal septum

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

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 ——–

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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