Paranasal sinuses and the ostiomeatal complex
- Applied anatomy
Four pairs of air spaces drain into the nose through small openings; when the openings swell shut, mucus stays in and sinusitis follows.
See it in 3D: Maxillary sinus · Frontal sinus · Ethmoid cells · Sphenoid sinus
What it is
The paranasal sinuses (maxillary, ethmoid, frontal and sphenoid) are air spaces in the bones around the nose and orbits, lined by ciliated mucosa that sweeps mucus to small openings (ostia). The frontal, maxillary and anterior ethmoid sinuses share one drainage pathway in the middle meatus, the ostiomeatal complex, so swelling there blocks several sinuses at once. Their age of development explains which sinusitis a child can have, and their position next to the orbit, teeth and brain explains the complications.
Applied anatomy
- Maxillary sinus: largest, in the cheek bone, above the roots of the upper back teeth; its opening is high on the medial wall, hidden by the uncinate process.
- Ethmoid cells: many small cells between the nose and the orbit; anterior cells drain to the middle meatus, posterior to the superior meatus.
- Frontal sinus: behind the forehead, drains down into the middle meatus.
- Sphenoid sinus: deep in the skull base behind the nose, drains to the sphenoethmoidal recess.
- Ostiomeatal complex: maxillary ostium, ethmoid bulla, ethmoid infundibulum, uncinate process and hiatus semilunaris.
Clinical physiology
- Sinuses warm and humidify air, produce mucus and lighten the skull.
- Cilia move mucus towards each ostium; blocked ostia or failing cilia let secretions stagnate and microbes grow.
- Sensation comes from the trigeminal nerve (frontal from V1, maxillary from V2), so sinus pain can be felt in the forehead, cheek or teeth.
Sinuses by age, drainage and typical complication
| Sinus | Present from | Drains to | Clinical point |
|---|---|---|---|
| Maxillary | Birth (aerated by about age 7) | Middle meatus | Cheek or upper tooth pain; odontogenic sinusitis |
| Ethmoid | Birth (aerated by about age 7) | Anterior: middle meatus; posterior: superior meatus | Next to the orbit: orbital cellulitis, the main complication in children |
| Sphenoid | About age 3 | Sphenoethmoidal recess | Deep, poorly localised headache; rare but serious complications |
| Frontal | About age 6, mature in adulthood | Middle meatus | Forehead pain; spread to bone or brain in adolescents and adults |
Clinical correlation
- Colds, allergies, a deviated septum, polyps and large adenoids block the ostia; cystic fibrosis and ciliary disorders impair clearance.
- Suspect bacterial sinusitis when symptoms last more than 10 days without improvement, start severe with high fever, or worsen after initial improvement.
- Green or yellow discharge alone does not prove bacterial infection.
- Complications are rare but serious: orbital cellulitis, bone infection, abscess and meningitis.
Next step / Initial management
- Diagnosis is clinical; no imaging for uncomplicated acute sinusitis.
- First line: saline irrigation, analgesics, intranasal corticosteroids; short use of topical decongestants only.
- Antibiotic only when bacterial criteria are met (persistent, severe or worsening course); aminopenicillin-based regimens are the usual first choice.
- Refer as an emergency (same day) for periorbital swelling, double vision or reduced vision, severe headache, confusion or neck stiffness.
- Refer routinely to ENT for symptoms over 3 months despite treatment, more than 2 to 3 episodes a year, unilateral polyps or bloody discharge, or loss of smell with obstruction.
Test yourself
Think of the answer, then tap the question to see it.
A 2-year-old has a swollen red eyelid after a cold. Which sinus is the usual source and why not the frontal?
The ethmoid sinus, which lies next to the orbit and is present at birth. The frontal sinus only appears around age 6.
Which three sinuses share the ostiomeatal complex in the middle meatus?
The frontal, maxillary and anterior ethmoid sinuses; swelling there can block all three at once.
An adult has one-sided maxillary sinusitis with foul discharge and a recent upper molar abscess. What is the likely origin?
Odontogenic sinusitis: the roots of the upper back teeth lie next to the maxillary sinus. The tooth must be treated as well as the sinus.
Connections
See it in 3D4
The structures of Durgical's 3D anatomy where it is found.
Educational content; it does not replace a medical assessment and is not a clinical instruction. For a real case, follow current guidelines and specialist advice.
Sources: Anatomy, Head and Neck, Nose Paranasal Sinuses (StatPearls (NCBI Bookshelf), 2023); Sinusitis (MedlinePlus, US National Library of Medicine, 2026); Smell Disorders (National Institute on Deafness and Other Communication Disorders (NIDCD), NIH, 2023).
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Representative model, for educational purposes only.