What is the detailed anatomy of the nose?

Detailed Anatomy of the Nose

The nose is a complex anatomical structure with significant variability across individuals, comprising external and internal components that serve crucial respiratory, olfactory, and defensive functions. 1

External Anatomy

• Nasal pyramid: Formed by paired nasal bones superiorly and upper lateral cartilages inferiorly
• Nasal tip: Supported by lower lateral cartilages (alar cartilages)
• Columella: The tissue bridge between the nostrils
• Nasal septum: Divides the nose into right and left cavities
  • Composed of cartilage anteriorly and bone posteriorly (perpendicular plate of ethmoid and vomer)
  • Septal deviation is extremely common, occurring in a high percentage of individuals 2, 1

Internal Anatomy

Nasal Cavity

• Vestibule: Anterior portion lined with skin containing vibrissae (nasal hairs)
• Nasal valve: Narrowest part of the nasal airway, critical for airflow regulation
• Turbinates (conchae): Three paired shelf-like structures on lateral walls
  • Superior, middle, and inferior turbinates
  • Covered with respiratory epithelium rich in vasculature
  • Middle turbinate variations include concha bullosa (pneumatized turbinate), which is one of the most common anatomical variants 2, 1
• Meatus: Passages beneath each turbinate
  • Inferior meatus: Drainage site for nasolacrimal duct
  • Middle meatus: Drainage site for anterior ethmoid, maxillary, and frontal sinuses
  • Superior meatus: Drainage site for posterior ethmoid cells

Paranasal Sinuses

• Maxillary sinuses: Largest sinuses, pyramidal in shape, located in maxillary bones
  • Drain into the middle meatus via the ostiomeatal complex
  • Accessory ostia are common variants 1
• Ethmoid sinuses: Collection of 3-15 air cells between the nasal cavity and orbit
  • Divided into anterior, middle, and posterior groups
  • Notable variants include:
    • Agger nasi cells (present in nearly all individuals) 2
    • Haller cells (infraorbital ethmoid cells)
    • Onodi cells (sphenoethmoidal cells) 2, 1
• Frontal sinuses: Variable in size and shape, located in frontal bone
  • Drain through the frontal recess into the middle meatus
• Sphenoid sinuses: Located in the body of sphenoid bone
  • Significant asymmetry is common 2
  • Important relationships to optic nerve, carotid artery, and pituitary gland

Functional Anatomy

• Mucociliary clearance: Coordinated ciliary movement transports mucus toward nasopharynx
• Nasal cycle: Physiological alternating congestion and decongestion of nasal passages 3
• Respiratory function: Warming, humidification, and filtration of inspired air
• Olfactory function: Specialized olfactory epithelium in superior nasal cavity

Surgical Landmarks and Boundaries

• Paranasal surgical box: Defines safe anatomical limits for endoscopic sinus surgery 4
  • Medial boundary: Middle turbinate
  • Lateral boundary: Orbital wall
  • Superior boundary: Skull base
• Vertical component: Defines frontal recess boundaries
  • Medial: Middle turbinate and intersinus septum
  • Lateral: Medial orbital wall and orbital roof
  • Anterior: Nasofrontal beak
  • Posterior: Skull base and posterior table of frontal sinus

Clinical Significance

• Anatomical variations are extremely common, with 67% of individuals presenting one or more variants 2
• Knowledge of these variations is essential for:
  • Safe endoscopic sinus surgery
  • Proper interpretation of imaging studies
  • Understanding patterns of sinus disease
• Variations differ among ethnic groups 1
• Critical structures at risk during surgery include:
  • Orbit and optic nerve
  • Internal carotid artery
  • Skull base and intracranial contents

Common Anatomical Variations

• Nasal septum deviation (most common variation)
• Concha bullosa (pneumatized middle turbinate)
• Septal spurs
• Agger nasi cells
• Onodi cells
• Haller cells
• Uncinate process variations
• Paradoxical middle turbinate
• Sinus aplasia or hypoplasia (less common)

Understanding these anatomical details is crucial for clinicians performing procedures in this region, as the high degree of variability necessitates careful preoperative assessment, typically with CT imaging, to prevent complications 2, 1.