Anterior and middle ethmoid

Abstract

The ethmoidal bulla is formed by the fusion between the middle and inferior turbinates and is the dorsal limit of the infundibulum. It contains the anterior and middle ethmoidal cells, while the agger nasi contains the most anterior of the anterior ethmoidal cells. Behind the bulla is the superior hiatus semilunaris, or retrobullar space, which is the space between the bulla and the basal lamella. The outlet for the ethmoidal cells contained in the bulla are multiple and are phylogenetically determined in each person. The manner in which they fuse embryologically, anatomical variations and their individual growth patterns, among other factors, will determine their final drainage sites. One must take into account that the ethmoidal bulla can grow or become pneumatized between the middle turbinate and the orbital wall, towards the cribiform plate. This makes the walls much thinner and as described by Keros and Onishi lead to dehiscence. The natural draining orifices of the ethmoid bulla can be systematized as follows: anterior, posterior and medial, posterior and superior. The anterior drainage site is found as a true natural ostium in the anterior aspect of the bulla. The discharge from the bulla in this case drains directly into the infundibulum. The most frecuent finding is to find it in the superior and lateral quadrant of the anterior wall of the bulla. The posterior and medial outlet is found in 81.5% of the cases and the content drains directly into the nasal cavity (Fig. 1). When the bulla has a posterior and superior drainage orifice, the mucus falls directly into the superior meatus or into a posterior and superior ethmoidal cell. In a diseased anterior ethmoid, these drainage sites are hampered, therefore it is necessary to exteriorize them (Fig. 2).