Frontal Sinus

Abstract

At the end of the fetal stage, the most anterior ethmoidal cells, still very small, are located near the hemifrontal orbital region, separated by the interfrontal or the metopic sutural space. These cells are lodged in soft connective tissue structures as individual epithelial invaginations. If a sinusal agenesis does not occur, after the second postnatal year at least one of these cells at either side will reach the frontal bone. By the fourth year, they are already radiographically detectable. From an embryological point of view, this sinus displays important and peculiar features with respect to the site in the nasal cavity where it opens and drains. The site of origin of every paranasal sinus in the nasal epithelium will also be the place where its drainage ostia will be. Wherever a cavity begins, it will grow in a genetically programmed fashion to occupy the most diverse anatomical areas, within the ethmoid itself or in the bones harboring other sinuses (Fig.102).