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

Anatomy of External Nose

Diagram: Osteocartilaginous Framework of External Nose

Introduction

Anatomy of the External nose is one of the most frequently tested topics in MBBS, ENT PG, NEET PG, FMGE and INI-CET examinations. A clear understanding of the osteocartilaginous framework, nasal valves, muscles, blood supply, nerve supply and lymphatic drainage is essential for understanding nasal fractures, rhinoplasty and nasal obstruction. This chapter provides concise, exam-oriented notes with labelled diagrams, clinical correlations and high-yield revision points.

Nasal skin

The skin over the nasal bones and upper lateral cartilages is thin and loosely adherent to the underlying framework. The skin over the nasal tip and alar cartilages becomes thicker and more adherent, and contains numerous sebaceous glands. It is the hypertrophy of these sebaceous glands that gives rise to a lobulated tumour called rhinophyma.

Nasal muscles (Facial Expression and Function)

The osteocartilaginous framework of the nose is covered by muscles that function to elevate, depress, compress, or dilate the nostrils and nasal tip.

• Nasal elevator muscles (Pull nose up) – Procerus, Levator labii-superioris alaeque nasi, Anomalous nasi muscles.
• Nasal depressor muscles (Pull tip down) – Alar nasalis and Depressor septi nasi.
• Compressor muscles (Close nostril) – Transverse nasalis.
• Dilator  muscles (Open nostril) – Dilator naris anterior.

All muscles of the external nose are supplied by branches of the facial nerve (cranial nerve VII).

Diagram: Nasal muscles

The Vestibule and Nasal Valve (The Airflow Regulator)

1. Vestibule

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 limen nasi marks the upper limit of the vestibule and marks the transition to the internal nasal valve region

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

2. Nasal Valve Area

Internal Nasal Valve Area

The internal nasal valve area is the narrowest part of the nasal airway and has the smallest cross-sectional area in the nose. Consequently, it is the most important site regulating nasal airflow and airway resistance during inspiration. Approximately 50–70% of the total nasal airway resistance occurs at this level.

The internal nasal valve is formed by the angle between the nasal septum and the caudal (lower) border of the upper lateral cartilage. Normally, this angle measures 10°–15°. Narrowing of this angle, such as after nasal trauma, previous rhinoplasty, or collapse of the upper lateral cartilage, can markedly increase nasal resistance and produce significant nasal obstruction.

Boundaries of the Internal Nasal Valve

• Laterally: The lower border of the upper lateral cartilage and fibrofatty tissue (along with the anterior head of the inferior turbinate).
• Medially: The cartilaginous nasal septum.
• Inferiorly (Floor): Nasal floor (anterior nasal sill region).

External Nasal Valve

The external nasal valve forms the entrance to the nasal airway and contributes significantly to nasal airflow during inspiration.

Boundaries of the External Nasal Valve

• Medially: Nasal septum (columella)
• Laterally: Alar rim, formed by the lateral crus of the lower lateral cartilage, sesamoid cartilages, and fibrofatty tissue
• Inferiorly: Nasal sill

Weakness or collapse of these supporting structures during inspiration can cause dynamic external nasal valve collapse, leading to nasal obstruction.

Parts of External Nose

The External nose is the first part of the upper respiratory tract and is responsible for warming, humidifying and filtering of inspired air.  It contains the peripheral organ of smell. The external nose opens anteriorly onto the face through the nostrils or nares.  It is a pyramidal projection in the mid-face with its root up and the base directed downwards. The nasal pyramid consists of an osteocartilaginous framework covered by muscles and skin.

It presents the following features:

1. Tip of the nose. It is the lower free end of the nose
2. Supratip. It is present just above the tip of the nose.
3. Root or bridge. It is the uppermost narrow part of the nose.
4. Nasion. It is the junction between the frontal bones and the nasal bones.
5. Rhinion. It is the junction between the nasal bones and cartilages.
6. Dorsum.
7. Nostrils or nares.
8. Ala. It is formed by alar cartilages.
9. Columella. It is the soft tissue bridge between the nostrils formed by the medial crura of the lower lateral cartilages.

Osteocartilaginous Framework (The Skeleton)

The skeletal framework of the nose determines its shape and structural integrity. Hence, understanding the bony and cartilaginous components is crucial for fracture management and rhinoplasty.

1. Bony Part (Upper One-Third)

The upper one-third of the external nose is bony, while the lower two-thirds are cartilaginous. The bony part consists of two small rectangular nasal bones that meet in the midline. It forms the bridge of the nose.

Boundaries of nasal bones:

• Superior Border: Articulates with the nasal process of the frontal bone.
• Inferior Border: Is related to the upper lateral cartilage (at the Rhinion).
• Lateral Border: Articulates with the frontal process of the maxilla.
• Medial Border: Articulates with the opposite nasal bone and forms a small part of the nasal septum.

 

2. Cartilaginous Part (Lower One-Third)

The nasal cartilages are hyaline cartilages that are attached to the bones to form the skeletal framework of the external nose.

It consists of:

1. Upper lateral cartilages. They are trapezoid-shaped and extend from the undersurface of the nasal bones (rhinion) above to the lower lateral cartilages and alar cartilages below. They fuse and attach to the upper border of the midline septal cartilage. The caudal free border of the upper lateral cartilage contributes to the internal nasal valve. Intranasally, the limen nasi marks the transition between the nasal vestibule and the nasal cavity. The upper lateral cartilage joins the lower lateral cartilage through the scroll area, an important anatomical junction that preserves nasal valve function and is frequently encountered during rhinoplasty.
2. Lower Lateral Cartilages (Alar Cartilages). Each lower lateral (alar) cartilage is U-shaped and is divided into medial, intermediate, and lateral crura. The medial crus lies within the columella, while the intermediate crus contributes to the nasal tip. The lateral crus forms the structural framework of the ala and overlaps the lower border of the upper lateral cartilage on each side. Together, the medial, intermediate, and lateral crura form the natural arch of the nasal ala.
3. Lesser alar (or sesamoid) cartilages. Two or more in number. They lie above and lateral to the alar cartilages. The various cartilages are connected with the adjoining bones by perichondrium and periosteum. Most of the free margin of the nostril is formed of fibrofatty tissue and not the alar cartilage.
4. Septal cartilage. Its anterosuperior border runs from under the nasal bones to the nasal tip. It supports the dorsum of the cartilaginous part of the nose. In a septal abscess or after excessive loss of septal support, as in a submucosal resection (SMR) operation, support of the nasal dorsum is lost and may produce saddle nose deformity.

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High-Yield Points

1. The upper one-third of the external nose is bony, whereas the lower two-thirds are cartilaginous.
2. The nasal bones form the bridge of the nose.
3. The upper lateral cartilage contributes to the internal nasal valve.
4. The internal nasal valve is the narrowest part of the nasal airway.
5. The normal internal nasal valve angle is 10°–15°.
6. Approximately 50–70% of total nasal airway resistance occurs at the internal nasal valve.
7. The scroll area connects the upper and lower lateral cartilages and is an important landmark during rhinoplasty.
8. The lower lateral cartilage has medial, intermediate and lateral crura.
9. The medial crus forms the columella.
10. The lateral crus supports the ala.
11. Most of the free margin of the nostril consists of fibrofatty tissue, not cartilage.
12. Loss of septal cartilage support causes saddle nose deformity.
13. The vestibule is lined by skin and contains vibrissae.
14. Limen nasi marks the transition from the vestibule to the nasal cavity.
15. The external nasal valve is formed mainly by the alar rim and nasal sill.
16. The muscles of the external nose receive motor supply from the facial nerve (CN VII).
17. Sensory supply comes from ophthalmic (V1) and maxillary (V2) divisions of the trigeminal nerve.
18. Blood supply arises from both the external carotid and internal carotid systems.
19. Infection of the nasal tip may spread to the cavernous sinus through valveless facial and ophthalmic veins.
20. Rhinophyma results from hypertrophy of sebaceous glands over the nasal tip.

Multiple Choice Questions 

1. Which structure forms the anatomical junction known as the Rhinion? A. Frontal bone and Nasal bone B. Nasal bone and Upper lateral cartilage C. Upper lateral cartilage and Septal cartilage D. Lower lateral cartilage and Alar cartilage
2. The most crucial area for regulating nasal airflow resistance on inspiration is: A. The Nares B. The Nasal Dorsum C. The Pharyngeal Isthmus D. The Nasal Valve Area
3. Infection of the nasal tip can pose a risk of spreading intracranially due to venous drainage into which of the following? A. Jugular vein B. Ophthalmic vein C. Superior sagittal sinus D. Internal maxillary vein
4. A patient develops a lobulated, bulbous nose due to severe hypertrophy of sebaceous glands. This condition is termed: A. Rhinitis Sicca B. Saddle Nose Deformity C. Rhinophyma D. Antrochoanal Polyp
5. Which cartilage’s excessive removal during a Septoplasty operation leads to a loss of dorsal support and a supratip depression? A. Lower lateral cartilage B. Upper lateral cartilage C. Septal cartilage D. Lesser alar cartilage
6. The medial boundary of the Nasal Valve Area is formed by the: A. Inferior turbinate B. Cartilaginous nasal septum C. Lateral crus of the lower lateral cartilage D. Fibrofatty tissue
7. The main sensory nerve supply to the Nasal Tip is a branch of the Ophthalmic Nerve (V1) known as the: A. Infraorbital nerve B. Supratrochlear nerve C. Anterior ethmoid nerve D. Maxillary nerve
8. Which border of the nasal bone articulates with the frontal process of the maxilla? A. Superior border B. Inferior border C. Medial border D. Lateral border
9. The coarse hairs in the vestibule of the nose, responsible for initial filtering of inspired air, are called: A. Cilia B. Microvilli C. Vibrissae D. Turbinates
10. The arterial supply to the nasal dorsum includes the external nasal branch of the anterior ethmoid artery, which originates from the: A. Internal carotid artery system B. External carotid artery system C. Facial artery D. Sphenopalatine artery

Answers and Explanations:

1. B. The Rhinion is the bony-cartilaginous junction between the nasal bones and the upper lateral cartilages.
2. D. The Nasal Valve Area is anatomically the narrowest part of the nasal airway, creating the most resistance.
3. B. The facial vein, which drains the danger area, communicates with the cavernous sinus via the ophthalmic vein.
4. C. Rhinophyma is the progressive, nodular enlargement of the distal nose caused by hypertrophy of sebaceous glands.
5. C. The Septal Cartilage provides the central columnar support for the cartilaginous nasal dorsum.
6. B. The septum forms the medial wall, while the ULC forms the superior-lateral wall.
7. C. The Anterior Ethmoid nerve is the nerve block target for anesthetizing the lower nasal bridge and the nasal tip.
8. D. The lateral border articulates with the frontal process of the maxilla. The superior articulates with the frontal bone.
9. C. Vibrissae are the stiff hairs in the nasal vestibule that act as the first line of defense against large particulates.
10. A. The anterior ethmoid artery is a terminal branch of the ophthalmic artery, which is a branch of the internal carotid artery.

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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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