General Medical Information

Ethmoid Sinuses

Susan D. John
Michael D. Maves

The ethmoid sinuses consist of a variable number of separate cavities that honeycomb the ethmoid bone between the upper part of the lateral nasal wall and the medial wall of the orbit. The anterior ethmoid cells are divided into frontal recess cells, which open into the frontal recess of the middle meatus; infundibular cells, which open into the ethmoid infundibulum; and bullar or middle ethmoid cells, which open directly into the middle meatus on or above the ethmoid bulla. There may be one to seven posterior ethmoid cells. The bullae and posterior ethmoid cells may encroach on each other and overlap, the bullar cells spreading backward or the posterior cells forward. The posterior ethmoid cells drain into the superior meatus.