At what age do the paranasal sinuses (maxillary, ethmoid, sphenoid, and frontal) typically form?

Age of Paranasal Sinus Formation

The paranasal sinuses develop sequentially during childhood, with ethmoid and maxillary sinuses present at birth, maxillary sinuses beginning significant pneumatization between birth and 12 months, frontal sinuses appearing around age 4-6 years, and sphenoid sinuses beginning development around age 3-4 years, with all sinuses reaching near-adult size by age 12-14 years. 1

Developmental Timeline by Sinus

Maxillary Sinus

• First to develop: The maxillary sinus is the first to begin significant pneumatization between birth and 12 months of age 1
• Present at birth and identifiable on radiographs in newborns 2
• The floor of the maxillary sinus reaches the level of the nasal floor by approximately 12 years of age 1
• Most extensive growth occurs during the first 8 years of life, with maximal dimensions reached by the end of the 16th year 3
• At birth, measures approximately 7.3 mm (length) × 4.0 mm (height) × 2.7 mm (width), expanding to 38.8 mm × 36.3 mm × 27.5 mm by age 16 4

Ethmoid Sinus

• Present at birth: Rudimentary ethmoid sinuses are already present at birth and can be identified on radiographs in 94% of newborns 2, 5
• Reach adult size at 12 to 14 years of age 1
• Growth periods are equal in both sexes 5

Frontal Sinus

• Develops later: Development begins later than maxillary and ethmoid sinuses 1
• Appears as a triangle at age 4 years and extends beyond the supraorbital margin at age 6 years 2
• Not aerated before age 6 years in most children 4
• Present in only 1.5% of newborns 5
• At age 16, measures approximately 12.8 mm × 21.9 mm × 24.5 mm 4
• Shows wide variation in size and shape, with growth periods lasting 2-3 years longer in males 5
• Definitive size differs by 17.1% between sexes 5

Sphenoid Sinus

• Develops later: Development begins later than maxillary and ethmoid sinuses 1
• Pneumatization starts around age 3-4 years after conversion from red to fatty marrow 4
• Begins to excavate the concha sphenoidalis at age 4 and becomes visible on radiographs at age 8 years when it extends to the hypophyseal fossa 2
• At age 3, measures approximately 5.8 mm × 8.0 mm × 5.8 mm, expanding to 23.0 mm × 22.6 mm × 12.8 mm by age 16 4
• Shows large variability in both size (up to 214% in one direction) and shape 5
• Definitive size differs by 5.4% between sexes 5

Clinical Implications

Age-Related Considerations

• By age 12, all sinuses almost reach their final sizes, though frontal and sphenoid sinuses show the most individual variation 2
• Gender-related differences in sinus dimensions become apparent after age 8 years, particularly in the maxillary sinus 3
• Understanding developmental timelines is critical when interpreting imaging studies in children, as absence of certain sinuses may be normal depending on age 1

Important Clinical Caveats

• Frontal and sphenoid sinus infections carry higher risk: Due to their anatomic location, infections in these sinuses have greater propensity to cause intracranial complications 1
• The sequential development means that younger children cannot develop sinusitis in sinuses that have not yet pneumatized (e.g., frontal sinusitis is not possible in children under 4-6 years) 2, 4
• The ostiomeatal complex is critical for drainage of maxillary, anterior ethmoid, and frontal sinuses, making this region most frequently involved in sinusitis 1