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There are three stages to the development of the optic canal:
1. There is the formation of the cartilaginous foramen during the third fetal month.
2. Then there is the ossification of the cartilaginous foramen.
3. Lastly, there is the transformation of the bony foramen into the bony canal.
This formation is part of the formation of the lesser sphenoid wing. The formation of the canal occurs initially laterally, then medially, and then the superior margin of the foramen.
There are 19 separate ossification centers in the sphenoid anlage. They are grouped into five areas. The areas are:
1. Lesser wing
2. Presphenoid
3. Postsphenoid
4. Greater wing
5. Pterygoid plate
An anterior and posterior strut are formed. The anteroinferior segment extends from the lesser wing to the posterosphenoid center. The posterosphenoid segment extends from the lesser wing to the presphenoid center. The result is a foramen with a keyhole appearance. It is not a functional foramen since no structure passes through it. It is a transition stage and becomes obliterated by the fusion of the two segments during the last two months of fetal life.
If the foramen between the anterior and posterior strut is not obliterated, we get a duplicated optic canal.
In the adult, the cranial opening is oval with the larger dimension in the horizontal plane. The orbital opening is oval with the largest dimension in the vertical plane. Therefore, the most accurate way to measure the size of a canal is in the horizontal plane.
Errors in identifying an optic canal can occur, mistaking it for a pneumatized clinoid process, posterior ethmoid air cell.carotico-clinoid foramen, defect in greater wing of sphenoid or an ectopic sphenoid cellule.
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A - anterior strut formed and posterior strut is beginning
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B - posterior is partially formed and gives "figure 8" appearance
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C - full posterior strut formed producing double optic canal
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D - space between anterior and posterior strut is ossified and only optic canal is left
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Figure 1 |
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A - X-ray similar to Figure 1A
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B - X-ray simular to Figure 1B
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C - X-ray similar to Figure 1C
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Figure 2 |
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A - skull demonstrating double canal
from orbital side with widest diameter
vertical
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B - same canal viewed from intracranial
side with longest diameter horizontal
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Figure 3 |
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X-ray of actual case
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Figure 4 | | 
