The postnatal development of the sphenoid bone is a complex dual process that involves:
- the forming of a single sphenoid bone through the rapid fusion of 5 separate ossification centers and 12 synchondroses that are present in the newborn.
- the pneumatisation of the sphenoid bone.
[1][2][3][4]
Non-pneumatised sphenoid sinus.
At birth the sphenoid bone is devoid of air.
[1]
In our study 8 newborns or infants aged from 6 days to 6 months had completely solid sphenoid bones.
The mean age of infants without pneumatisation was 2 months.
(Fig.1) (Fig.2)
Conchal or fetal pneumatisation.
The first step in pneumatisation is the development of the sphenoidal conchae from the paired ossicles of Bertin that fuse to the rostrum at the anterior end of the presphenoid bone,
at the site of the homonymous synchondrosis.
During or after this process,
nasal mucosa invaginates into sphenoidal conchae bilaterally and they progressively become aerated.
This is the most rudimentary pattern of sphenoidal pneumatisation called conchal or fetal and is confined in the rostrum.
[1][3][5][6][7]
In our study beginning of aeration was identified as a single aerated sphenoidal concha in a 2-month-old male infant (Fig.2).
The youngest infant with bilateral complete aerated sphenoidal conchae was a 7-month-old female (Fig.3).
Conchal pattern of aeration was identified in 43 children with ages ranging from 7-months to 8 years and mean age 2,5 years.
(Fig.4)
Presellar or juvenile pneumatisation.
Pneumatisation continues in the presphenoid bone in a posterior direction extending as far as the intersphenoidal synchondrosis (anterior sella turcica wall).
This pattern is called presellar or juvenile.
The bone formed at the line of fusion of two bony centers,
in this case the presphenoid and postsphenoid centers,
is believed to be denser and more resistant than the tissue on either side of that line.
This fact would account for the restriction of the sinus to the pre-sphenoid during childhood.
[1][3][4][5][6][8]
In our study the presellar pattern was observed in 21 children aged 3-9 years,
with mean age 5,4 years.
The craniopharyngeal canal remnant served as an indicator for the position of the intersphenoidal synchondrosis,
in order to establish the pattern. (Fig.5)
Sellar or adult pneumatisation.
Sphenoid sinus continues to expand posteriorly in the postsphenoid bone.
It lies under the sellar floor and is considered to have taken the adult,
mature configuration.
Thus this pattern is called sellar or adult.
As with the presellar pattern and the barrier of the intersphenoidal synchondrosis,
the sellar pattern extends to but not beyond the spheno-occipital synchondrosis.
[1][3][5][6][9][10]
The sellar or adult pattern was found in our study in 32 children aged 6-15 years,
with mean age 10,5 years.
All children ≥10 years showed adult pattern of pneumatisation. (Fig.6)
Aeration beyond the postsphenoid bone was observed in 13 children aged 6-15 years old.The sphenoid sinus extended to the lateral recess (greater sphenoid wing) in all children and additionally to the pterygoid process in 3 children and to the anterior and posterior clinoid processes in 1 child.
Extension of the sinus to the basioccipital bone has been known but could not be as evaluated due to the age range of our study group and the time of closure of the spheno-occipital synchondrosis.
Our study was restricted to the pediatric population and the spheno-occipital synchondrosis showed complete closure the earliest at the age of 12 and the latest at the age of 15.
(Fig.7)
Pathology
The most common pathology that was observed incidentally was sinusitis,
which was observed independently of the pattern of pneumatisation. The younger patient with opacified sinus was 3-years-old and had conchal sphenoid sinus.