| Abstract: |
The paranasal sinuses are really extensions of the nasal cavity as air filled spaces into the skull bones. Classic anatomic treatises attribute initial paranasal sinus development to lateral nasal wall ridges called ethmoturbinals. A series of five to six ridges first appear during the eighth week of development; through regression and fusion, however, three to four ridges ultimately persist.The first ethmoturbinal regresses during development; its ascending portion forms the agger nasi, while its descending portion forms the uncinate process. The second ethmoturbinal ultimately forms the middle turbinate, the third ethmoturbinal forms the superior turbinate, and the fourth and fifth ethmoturbinals fuse to form the supreme turbinate. These structures are all considered to be ethmoid in their origin. An additional ridge, the maxilloturbinal, arises inferior to these structures; This ridge ultimately forms the inferior turbinate but it is not considered ethmoid in its embryologic origin.The primary furrows that lie between the ethmoturbinals form the various nasal meati and recessesThe second primary furrow forms the superior meatus and the third primary furrow forms the supreme meatus. As development progresses, secondary evaginations and invaginations emerge from the lateral nasal wall between the maxillo- and ethmo-turbinal.
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