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The maxillary sinuses are the first of the paranasal sinuses to develop. In the neonate, the maxillary sinuses are quite small and may be partially or completely opacified. The maxillary sinuses grow progressively until the end of puberty. They reach the plane of the hard palate by 9 years of age. Asymmetry of the maxillary sinuses is common. The drainage ostium of the maxillary sinus is located superomedially. It empties into the infundibulum, which is located between the lamina papyracea and the uncinate process. The infundibulum opens into the middle meatus through the hiatus semilunaris. The maxillary sinuses become visible on standard radiographs at approximately 2 to 3 months of age.1,2

Small anterior ethmoid air cells are present at birth. There is rapid progression in ethmoid sinus development during the first 2 years of life. A second phase of rapid development occurs just before puberty. Pneumatization occurs from an anterior to posterior direction. Complete development occurs by the age of puberty. Each mature ethmoid sinus is bounded superiorly by the floor of the anterior cranial fossa, and laterally by the orbital wall. Aeration of the ethmoid sinuses is first radiographically identified at 3 to 6 months of age. Posterior ethmoid air cell aeration is first visible around the age of 6 or 7 years.

The sphenoid sinuses are tiny marrow-filled cavities at birth. Pneumatization usually begins around 2 years of age, and progresses until puberty. The mature sphenoid sinuses are bounded by the dura and sella superiorly, the cavernous sinuses laterally, posterior ethmoid air cells anteriorly, and the clivus posteriorly. The sphenoid sinuses are visible on radiographs beginning at 1 to 2 years of age.

The frontal sinuses originate as extensions from the anterior ethmoid air cells. Development begins around the age of 2 years, and growth continues until the end of puberty. The frontal sinuses have the greatest degree of developmental variation of any of the paranasal sinuses. Frontal sinus aeration can usually be identified on radiographs beginning at 4 to 8 years of age.

The frontal, anterior ethmoid, and maxillary sinuses drain through the ostiomeatal complex (ostiomeatal unit). There is no clear consensus as to the precise anatomic definition of the ostiomeatal complex. Most authors include the ethmoid infundibulum, middle nasal meatus, ethmoid bulla, nasofrontal recess, and ostia of the anterior ethmoidal, maxillary, and frontal sinuses as components. The hiatus semilunaris as is an opening in the lateral nasal wall adjacent to the uncinate process that allows communication with the middle meatus, which is the space in the nasopharynx inferior to the middle turbinate. The posterior ethmoid air cells and the sphenoid sinus drain into the superior meatus, which is below the superior turbinate. The nasolacrimal duct drains into the inferior meatus.

Developmental variations of the nasopharynx and paranasal sinuses are common. Most are of no clinical significance. Some of ...

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