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Ethmoidal foramina: the rule 24-12-6: is it true for Indian orbits?
Authors: GM Preethi, M Subrahmanyam
Number of views: 435
Aim : The literature states that the distances between the medial margin of the orbit to the anterior ethmoid
foramen, from it to the posterior ethmoid foramen and from it to the optic canal are 24mm, 12mm & 6 mm. This study is to
verify if this is true in the Indians as there is no data available in the literature. To the best of our knowledge it is the first study
from India, which focused on the relationship of ethmoid foramina. Methods: 70 orbits of 35 Indian skulls were studied, using
depth gauge, sliding calipers, dividers and metal scale by a single observer. Results: The average distance between the medial
margin of the orbit and the anterior ethmoid foramen is 21.30mm and 20.37mm for right and left orbits respectively (range
varying from 18 to 26mm in the right and from 14 to 26 in the left orbit). The average distance between the anterior and
posterior ethmoid foramina is 12.45 and 12.47mm (range 6mm to 18mm). The average distance between the posterior ethmoid
foramen and the optic canal is 6.32 and 7.37mm (range 2 mm to 18mm). 10 of 35 skulls (28.6%) had 3 foramina instead of 2
(accessory foramen), involving right orbit in 5, left in 4 and both the orbits of a skull. Conclusions: The rule 24-12-6 does not
apply to Indian orbits. The anterior Ethmoid foramen is about 3mm nearer to the orbital margin. There is a great variation in the
distances of ethmoid foramina. Nearly a third of the skulls have accessory ethmoid foramen.