the composition of fetal skull and component of it

1. Damanhuruniversity.
Facultyof nursing.
Obstetric&gynecology
Department .
2014 /2015.
Prepared by :…….
Mariem abd
elfatah

2. The fetal skull
The fetal skull is the most difficult part of the baby to pass through the
mother’s pelvic canal, due to the hard bony nature of the skull.
Understanding the anatomy of the fetal skull and its diameter will help you
recognise how a labour is progressing, and whether the baby’s head is
‘presenting’ correctly as it comes down the birth canal. This will give you
a better understanding of whether a normal vaginal delivery is likely, or if
the mother needs referral because the descent of the baby’s head is not
making sufficient progress.
Importance of the fetal skull:
1. Largest part of the fetal body.
2. Most frequent [resenting part of the fetus.
3. Least compressible of all fetal parts.
Fetal skull bones :
The skull bones encase and protect the brain, which is very delicate and
subjected to pressure when the fetal head passes down the birth canal.
Correct presentation of the smallest diameter of the fetal skull to the
largest diameter of the mother’s bony pelvis is essential if delivery is to
proceed normally. But if the presenting diameter of the fetal skull is larger
than the maternal pelvic diameter, it needs very close attention for the
baby to go through a normal vaginal delivery.

3. Cranial bones :
The fetal skull is made up of six cranial bones which are the following:
1. Sphenoid
2. Ethmoid
3. Temporal
4. Frontal
5. Occipital
6. Parietal
The frontal, occipital and the parietal cranial bones could either be fetal presenting
part if the presentation is vertex.
The fetal skull bones are as follows:
 The frontal bone, which forms the forehead. In the fetus, the frontal bone is in
two halves, which fuse (join) into a single bone after the age of eight years.
 The two parietal bones, which lie on either side of the skull and occupymost
of the skull.
Parietal is pronounced ‘parr eye ett al’. Occipital is pronounced ‘oxipp itt al’.
 The occipital bone, which forms the back of the skull and part of its base. It
joins with the cervical vertebrae (neck bones in the spinal column, or
backbone).
 The two temporal bones, one on each side of the head, closest to the ear.
Understanding the landmarks and measurements of the fetal skull will help you to
recognize normal and abnormal presentations of the fetus during antenatal
examinations, labor and delivery.

4. Anatomy of the Fetal Skull It consists of
vault, face , base.
The vault :
Vault(cranium): to overlap under pressure and to change shape to confirm to the
maternal pelvis (molding)
 ---thin
 ---weakly ossified
 ---easily compressible
 ---interconnected by membranes
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.
The face :
The face is the area from the junction of the chin and neck to the root of the nose and
supra-orbital ridges .it composed of14 small bones.
The base :
 Base: to protect the vital structures
 ---large
 ---ossified
 ---firmly united
 ---noncompressible
SUTURE:the
at bones of the vault are united together by the non-osssified membranes attached to
the margins of the bones. These are called SUTURE.
, over the other during moulding of the headpermits gliding movement of one bone

5. Sutures are joints between the bones of the skull. In the fetus they can ‘give’ a little
under the pressure on the baby’s head as it passes down the birth canal. During early
childhood, these sutures harden and the skull bones can no longer move relative to
one another, as they can to a small extent in the fetus and newborn.
 The lambdoid suture forms the junction between the occipital and the frontal
bone.
 The sagittalsuture joins the two parietal bones together.
 The coronal suture joins the frontal bone to the two parietal bones.
 The frontal suture joins the two frontal bones together.
The Fontanels :
A fontanel is the spacecreated by the joining of two or more sutures. It is covered by
thick membranes and the skin on the baby’s head, protecting the brain underneath the
fontanel from contactwith the outside world. Identification of the two large fontanels
on the top of the fetal skull helps you to locate the angle at which the baby’s head is
presenting during labor and delivery.
Or Definition :the membrane-filled spacelocated at the point where the sutures
intersect.
The most important of which are the anterior and posterior fontanelles.
More useful in diagnosing the fetal head position than sutures

6. The anterior fontanel (also known as the bregma) is a diamond-shaped (2 × 3 cm)
spacetowards the front of the baby’s head, at the junction of the sagittal, coronaland
frontal sutures. It is very softand you can feel the fetal heart beat by placing your
fingers gently on the fontanel. Ossified at 18-24 month after birth. Floor is made by
a membrane. Its palpation thru internal examination. . ICP can be roughly assessed
from its condition after birth. Depression in dehydration and bulging in raised ICP.
The posteriorfontanel (or lambda) has a triangular shape, and is found towards the
back of the fetal skull. It is formed by the junction of the lambdoid and sagittal
sutures. closes at 6 to 8 weeks of life . From its relation of the maternal pelvis,
position of vertex is determined. Internal rotation can be assessed from its location
PosteriorFontanelle (Lambda)Anterior Fontanelle (Bregma)
Small and triangular.Large, and lozenge-shaped.
Its floor is bony.Its floor is membranous.
Surrounded by 3 bones.Surrounded by 4 bones.
(2 parietal and occipital).(2 frontal and 2 parietal).
The floor is completely ossifiedat full
term.
The floor is completely ossified 1.5 years
after birth.
The surrounding bones are
overlapping during molding.
The surrounding bones are not
overlapping during molding.

7. Regions and landmarks in the fetal skull :
The vertex is the area midway between the anterior fontanel, the two parietal bones
and the posterior fontanel. A vertex presentation occurs when this part of the fetal
skull is leading the way. This is the normal and the safest presentation for a vaginal
delivery.
The brow is the area of skull which extends from the anterior fontanel to the upper
borderof the eye. A brow presentation is a significant risk for the mother and the
baby.
The face extends from the upper ridge of the eye to the nose and chin (lower jaw). A
face presentation is also a significant risk for the mother and baby.
The occiputis the area between the base of the skull and the posterior fontanel. It is
unusual and very risky for the occiput to be the presenting part.
Diameter of fetal skull :
Anteroposterior diameters:
 Suboccipito-bregmatic = 9.5cm
o from below the occipital protuberance to the centre of the anterior
fontanelle (bregma).

8. o It is the engagement diameter in occipito-anterior with complete flexion.
Suboccipito-frontal = 10 cm
o from below the occipital protuberance to the anterior end of the bregma.
o It is the engagement diameter in occipito anterior with incomplete
flexion.
o 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
o form the occipital protuberance to the root of the nose.
o It is the engagement diameter in occipito-posteriorposition.
o It is the diameter that distends the vulva in face to pubis delivery.
o It is the diameter that distends the vulva if the head extends before
crowing in occipito anterior.
 Mento-vertical =13.5 cm
o from the tip of the chin to the vertical point.
o 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.
 Submento-vertical =11.5 cm
o 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.
o It is the engagement diameter in the incompletely extended face.
o It is the diameter that distends the vulva during face delivery.
 Submento-bregmatic = 9.5 cm
o from the junction of the chin and neck to the centre of the bregma.
o It is the engagement diameter in face presentation when the head is
completely extended.
Transverse diameters :
 Biparietal =9.5 cm
o between the 2 parietal eminencies.
 Bitemporal = 8 cm
between the anterior ends of the temporal sutures .
molding :
is the change in the shapeof the head as a resultof the softskullbones overlapping
each other because they are not firmly united and movement is possible.

9. Caput Succedaneum:
Is edema of the scalp resulting frompressureduring labor .or formation of an
edematous swelling over the presenting partof fetal head .
Cephalhematoma:
Itis a collection of blood between periosteum of skull bone and bone it self swelling
not present at birth develops after 24 to48 hr after .

10. CephalhematomaCaput Succedaneum
Rupture of periostal
capillary .
Instrumental delivery .
Trauma .
Difficult or prolonged
labor.
Causes
Several hours after
birth increase
in size for 2-3
At birth no increase in sizeAppears
Approximately 6 weeks
after birth
Several days after birthDisappears
Never cross the suture
line
Cross the line sometimesExtent
Marked, well definedVague, poorly definedBorder
Jaundice, underlying
skull fracture,
intracranial bleeding
, shock
Rarely anemia or jaundiccomplication
Observationfor
affected part.
Bloodtransfusionand
phototherapy may
necessary.
No specific treatmentTreatment

11. References :
www.freelivedoctor.com
http://www.open.edu/openlearnworks/mod/oucontent/view.php?id=36
&printable=1
http://www.nlm.nih.gov/medlineplus/ency/imagepages/1127.htm
http://www.anatomyexpert.com/structure_detail/140/984/
http://en.wikipedia.org/wiki/Fetal_head
https://embryology.med.unsw.edu.au/embryology/index.php?title=Musc
uloskeletal_System_-_Skull_Development