An osteologic study of human ethmoidal foramina with special reference to their classification and symmetry.

The present investigation was designed to study the anatomy of the ethmoidal foramina in adult human dry skulls. In addition to investigate the number of ethmoidal foramina that can be found on the orbital wall, we also addressed their classification and symmetry. The analy- sis of 1089 orbits demonstrated that the average number of ethmoidal foramina/orbit was 2.07 (range 0 to 4). As for their classification, we devised the relative depth index (RDI) to differenti- ate the anterior from the posterior ethmoidal foramina. The index represents the ratio "distance of the foramen from the anterior lacrimal crest/length of the medial orbital wall". The average index of the anterior and posterior ethmoidal foramina were 0.53±0.04 and 0.84±0.06 respective- ly. As the mean of the two indexes was 0.685, we used the latter value as a sort of numerical watershed to define the domains of the anterior and of the posterior ethmoidal foramina on the orbital wall. Thus all ethmoidal foramina with an RDI : 0.68 were considered anterior ethmoi- dal foramina and all ethmoidal foramina with an RDI 0.69 were considered posterior ethmoi- dal foramina. In this way it is possible to properly classify foramina on orbits with 1,.3 or 4 ethmoidal foramina. As for their symmetry, in contrast to what had been previously reported, we observed that in most cases ethmoidal foramina have a highly symmetric arrangement both in terms of number of foramina on fellow orbits and of position along the orbital wall.