Where are the sinus cavities located?

Anatomical Location of the Paranasal Sinuses

The paranasal sinuses are air-filled cavities located within specific bones of the skull, surrounding the nasal cavity, with four distinct paired groups: the maxillary sinuses in the cheekbones, ethmoid sinuses between the eyes, frontal sinuses in the forehead, and sphenoid sinuses behind the ethmoids at the center of the skull base. 1

Detailed Anatomy of Each Sinus Group

Maxillary Sinuses

• Located within the maxillary bone (cheekbones)
• Largest of the paranasal sinuses
• First to develop, beginning pneumatization between birth and 12 months
• Floor reaches the level of the nasal floor by approximately 12 years of age
• Drain through the ostiomeatal complex into the middle meatus
• Bordered by:
  • Floor: alveolar process of maxilla (roots of upper molars may project into it)
  • Roof: orbital floor
  • Medial wall: lateral nasal wall
  • Lateral wall: zygomatic process of maxilla 1

Ethmoid Sinuses

• Located between the eyes in the ethmoid bone
• Present as rudimentary structures at birth
• Reach adult size by 12-14 years of age
• Divided into anterior and posterior groups:
  • Anterior ethmoid cells drain into the middle meatus via the ostiomeatal complex
  • Posterior ethmoid cells drain into the superior meatus
• Most frequently involved in sinusitis due to their location and drainage patterns 1

Frontal Sinuses

• Located in the frontal bone above the eyes and nasal bridge
• Develop later than maxillary and ethmoid sinuses
• Drain through the frontal recess into the middle meatus via the ostiomeatal complex
• Significant anatomical variation in size and symmetry between individuals
• Due to their location, infections here have greater propensity to cause intracranial complications 1

Sphenoid Sinuses

• Located in the body of the sphenoid bone at the center of the skull base
• Positioned posterior to the ethmoid sinuses and nasal cavity
• Drain into the sphenoethmoidal recess
• Have critical adjacent structures:
  • Optic nerve
  • Cavernous sinus
  • Carotid artery
• Infections or tumors here can affect these vital structures 1

Functional Drainage Pathways

The sinuses are organized into functional drainage systems:

1. Anterior Functional Cavity:

   • Maxillary, anterior ethmoid, and frontal sinuses
   • All drain through the ostiomeatal complex into the middle meatus
   • Obstruction of this complex can lead to sinusitis in all three sinus groups 1, 2

2. Posterior Functional Cavity:

   • Posterior ethmoid sinuses
   • Drain into the superior meatus 2

3. Sphenoidal Functional Cavity:

   • Sphenoid sinuses
   • Drain into the sphenoethmoidal recess 2

Sinus Physiology

• Sinuses are lined with pseudostratified, ciliated columnar epithelium interspersed with goblet cells
• Cilia beat to sweep mucus toward the ostial openings
• Ostial obstruction can lead to:
  • Mucus impaction
  • Decreased oxygenation (facilitating bacterial growth)
  • Pressure changes causing pain
  • Development of sinusitis 1

Clinical Significance

• The anatomical arrangement makes the anterior ethmoid sinuses and middle meatus (ostiomeatal complex) most frequently involved in sinus disease
• Anatomic variations or abnormalities within the ostiomeatal complex can predispose to sinusitis
• Frontal and sphenoid sinus infections have greater potential for intracranial complications due to their proximity to the brain
• Sphenoid sinus pathology can affect the optic nerve, cavernous sinus, and carotid artery 1

Understanding the precise location and relationships of the paranasal sinuses is essential for proper diagnosis and management of sinonasal diseases, as well as for safe surgical intervention when necessary.