Sphenoidal Sinus

1. Overview

The sphenoidal sinus is one of the four paired paranasal sinuses, located within the body of the sphenoid bone, deep in the skull. These air-filled cavities are lined with mucosa and communicate with the nasal cavity. Although small and well-protected, the sphenoidal sinuses are clinically significant due to their proximity to vital neurovascular structures. Like other paranasal sinuses, they contribute to respiratory air conditioning, voice resonance, and mucociliary clearance.

2. Location

The sphenoidal sinuses are located:

• Within the sphenoid bone, at the base of the skull

• Posterior to the nasal cavity, behind the superior nasal conchae

• Inferior to the sella turcica, which houses the pituitary gland

Key anatomical relationships:

• Superiorly: Pituitary gland and optic chiasm

• Laterally: Cavernous sinuses and internal carotid arteries

• Posteriorly: Clivus and brainstem

• Anteriorly: Opens into the sphenoethmoidal recess in the superior nasal meatus

3. Structure

The sphenoidal sinuses vary in size and shape among individuals and may be asymmetrical. Key features include:

• Thin-walled air cavities that begin as small pits at birth and expand with age

• Mucosal lining: Ciliated pseudostratified columnar epithelium with goblet cells (respiratory mucosa)

• Ostium: A small opening that drains the sinus into the sphenoethmoidal recess above the superior nasal concha

• Variable pneumatization: In some individuals, the sinus may extend into surrounding structures such as the clivus or greater wings of the sphenoid

4. Function

Though their precise function remains partially theoretical, sphenoidal sinuses share several known roles with other paranasal sinuses:

• Air filtration and humidification: Aid in conditioning inspired air by warming and moistening it

• Reduction of skull weight: Help lighten the overall mass of the skull

• Voice resonance: Contribute to the tonal quality and resonance of the voice

• Mucus drainage: Produce mucus that drains into the nasal cavity, assisting in air purification

5. Physiological Role(s)

The sphenoidal sinuses support several physiological functions relevant to respiratory and cranial systems:

• Mucociliary clearance: Cilia propel mucus and trapped particles toward the nasal cavity

• Immune defense: Mucosal lining contains immune-active cells that help defend against airborne pathogens

• Pressure modulation: Equalize intranasal air pressure with external pressure to protect cranial structures

• Thermal insulation: Sinus air acts as a buffer protecting surrounding neurovascular structures from temperature fluctuations

6. Clinical Significance

Sphenoid Sinusitis

Inflammation or infection of the sphenoidal sinus, though less common than maxillary or frontal sinusitis, can be serious due to proximity to vital structures. Symptoms may include:

• Deep-seated or vertex headache

• Postnasal drip

• Visual disturbances if the optic nerve is involved

Diagnosis: CT scan or endoscopic examination
Treatment: Nasal decongestants, antibiotics, and surgical drainage if necessary

Mucocele

A benign cystic lesion caused by blockage of the sphenoidal sinus ostium. Expansion can compress adjacent structures, including:

• Optic nerve (causing visual loss)

• Pituitary gland (leading to hormonal symptoms)

Surgical marsupialization or drainage may be required.

Transsphenoidal Surgery

Surgeons often access the pituitary gland through the sphenoidal sinus using an endonasal transsphenoidal approach. Accurate knowledge of sphenoidal sinus anatomy is critical to avoid complications involving:

• Optic chiasm

• Internal carotid arteries

• Cavernous sinus

Sinus Fungal Infections

In immunocompromised patients (e.g., uncontrolled diabetes, transplant recipients), invasive fungal infections such as aspergillosis can involve the sphenoidal sinus and spread to the orbit or brain, causing:

• Proptosis

• Visual loss

• Cavernous sinus thrombosis

Requires urgent antifungal therapy and surgical debridement.

CSF Rhinorrhea

Injury to the thin sinus roof (especially during surgery) can lead to cerebrospinal fluid leakage into the nasal cavity. Presents as clear, watery nasal discharge and increases risk for meningitis.