Obstetrics Simplified - Diaa
Anatomy of the Foetal Skull
It consists of vault, face and base.
The vault is composed of:
- 2 frontal bones separated by the frontal suture,
- 2 parietal bones separated by the sagittal suture,
- the occipital bone separated by the lambdoidal suture from
the parietal bones, while the coronal suture separates the frontal from
the parietal bones.
Each of the 2 parietal bones is separated from the temporal bone on each
side by the temporal suture.
The face is the area from the junction of the chin and neck to the root
of the nose and supra-orbital ridges.
The vertex is the area of the vault bounded ;
- anteriorly by the anterior fontanelle and the coronal suture,
- posteriorly by the posterior fontanelle and lambdoidal suture,
- laterally by 2 lines passing by the parietal eminencies.
The brow is the area from the nose and supra-orbital ridges to the anterior
fontanelle and coronal suture.
These are 6 areas lie at the meeting of the sutures. Four fontanelles
lie at the anterior and posterior end of the temporal sutures on each side
and have no obstetric importance. The anterior and posterior fontanelles
are important to diagnose:
- the vertex presentation,
- the position of the occiput,
- the degree of flexion of the head.
|Large, and lozenge-shaped.
||Small and triangular.
|Its floor is membranous.
||Its floor is bony.
|Surrounded by 4 bones.
||Surrounded by 3 bones.
|(2 frontal and 2 parietal).
||(2 parietal and occipital).
|The floor is completely
ossified 1.5 years after birth.
||The floor is completely
ossified at full term.
|The surrounding bones
are not overlapping during moulding.
||The surrounding bones
are overlapping during moulding.
Diameters of Foetal Skull
- Suboccipito-bregmatic = 9.5cm
- from below the occipital protuberance to the centre of the anterior
- It is the engagement diameter in occipito-anterior with complete
- Suboccipito-frontal = 10 cm
- from below the occipital protuberance to the anterior end of
- It is the engagement diameter in occipito anterior with incomplete
- It is the diameter that distends the vulva in occipito anterior
if the head is allowed to extend after crowning.
- Occipito-frontal = 11.5 cm
- form the occipital protuberance to the root of the nose.
- It is the engagement diameter in occipito-posterior position.
- It is the diameter that distends the vulva in face to pubis
- It is the diameter that distends the vulva if the head extends
before crowing in occipito anterior.
- Submento-bregmatic = 9.5 cm
- from the junction of the chin and neck to the centre of the
- It is the engagement diameter in face presentation when the
head is completely extended.
- Submento-vertical =11.5 cm
- from the junction of the chin and neck to the vertical point
which is a point on the sagittal suture midway between anterior
and posterior fontanelles.
- It is the engagement diameter in the incompletely extended face.
- It is the diameter that distends the vulva during face delivery.
- Mento-vertical =13.5 cm
- from the tip of the chin to the vertical point.
- It is the engagement diameter in brow presentation. As it is
longer than the largest diameter of the pelvic brim, the head cannot
enter the pelvis.
- Biparietal =9.5 cm
- between the 2 parietal eminencies.
- Subparietal supraparietal = 9cm
- from below one parietal eminence to above the opposite eminence.
- It is the engagement diameter in case of asynclitism.
- Bitemporal = 8 cm
- between the anterior ends of the temporal sutures./li>
- Bimastoid = 7.5cm
- between the tips of the 2 mastoid processes.
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Edited by Aldo Campana,