Dynamics of optic canal and orbital cavity development revealed by microCT

Numerous studies have attempted to clarify the exact anatomy and variations of the optic canal with non-conclusive results due to its close proximity to many vulnerable structures. We sought to determine the dynamics of growth and development of these structures on fetal skulls, which will help us to better understand of gender and age-dependent variations, as well as fatal malformations.

Fifteen previously macerated fetal frontal and sphenoid bones were analyzed and the diameters of optic canal, and distance of orbit from frontomaxillary suture to frontozygomatic suture were measured using 3D reconstruction images obtained by micro-CT.

Average diameter of the optic canal in 300 mm fetus was measured to be 1,546 ± 36 µm, in 400 mm fetus 2,470 ± 123 µm and in 500 mm fetus 3,757 ± 203 µm. This trend indicates a linear enlargement of optic canal during the fetal period. During the same time period, diameter of the orbit enlarges from 12,319 ± 559 µm in 300 mm fetus to 19,788 ± 736 µm in 500 mm fetus. Growth curve is significantly lower in comparison with the same curve in optic canal data. We also calculated the ratio of orbit diameter and optic canal diameter between those groups which decreased from a value of 7.9 ± 0.4 for 300 mm fetus to 5.3 ± 0.2 for 500 mm fetus.

Dynamics of optic canal and orbital cavity development is different in early and late fetal period. Diameters of those structures are in better correlation with the fetal length.